Microstructure Research: Cleanroom Linz

Various activities taking place in the cleanroom are described, such as MBE growth of group IV heterostructures, of II-VI and IV-VI compounds, surface analysis by UHV-STM and Auger spectroscopy, as well as lateral patterning by photolithography and reactive ion etching for fabrication of infrared detectors, quantum wires and dots.

MBE of Si/Si1-xGex and of Si/Si1-yCy Heterostructures

In the last couple of years intensive studies on Si/SiGe heterostructures and quantum wells have been reported by several groups. Apart from the investigation of fundamental physical properties of Si-based heterostructures as opposed to III-V compounds, the driving force behind these studies was the hope for an improvement of devices based on Si/SiGe in comparison to conventional Si homostructures. Indeed, Si/SiGe heterobipolar transistors with high-frequency properties superior to conventional Si devices were fabricated as well as Si/SiGe based MODFET's.

Recently another class of Si based heterostructures, namely Si/Si1-yCy, has attracted a lot of interest because it can extend the possibilities to other applications than offered by Si/SiGe. In 1995, in the clean room of the semiconductor physics group at Linz a RIBER SIVA 45 MBE has been installed for the growth of Si/Ge/C heterostructures. It is equipped with three e-beam evaporators for Si, Ge, and C. For n-and p-doping effusion cells for antimony and boron are available. The beam fluxes are monitored by a Hiden quadrupole mass spectrometer, which is also used for a feedback regulation of the evaporator. Compared to a carbon filament source, the e-beam evaporator for carbon has a much higher capacity and in principle the possibility to use higher C-fluxes.

So far, Si/SiGe heterostructures and quantum well structures were grown with this MBE, as well as Si/Si1-yCy layers, MQW's and superlattices. Also strain compensated Si1-xGex/Si1-yCy superlattices were fabricated and structurally investigated. In particular, silicon/carbon/silicon superlattices were grown, with the C-layers confined to about one monolayer, but with extremely high carbon contents. The structural data of these superlattices as obtained from high-resolution X-Ray diffraction, transmission electron microscopy, and reciprocal space mapping indicate a satisfactory quality, not much inferior to pseudomorphic Si/SiGe superlattices.

The electrical properties of the Si1-yCy layers are dominated so far by a background electron concentration of 4x1016 cm-3 with mobilities comparable to those of similarly doped Si. In the epilayers no evidence was found for a mobility reduction due to the strong lattice deformation around the C-lattice sites.

At the moment, Si-shields are inserted into the MBE system in order to reduce the background doping substantially, a requirement for achieving high carrier mobilities.

A preliminary attempt was made to grow modulation doped Si/ Si1-yCy heterostructures. On top of a (001) Si substrate, after depositing a 1 mm thick Si buffer layer (undoped), a 17 nm thick Si0.98C0.02 layer was deposited followed by a 12 nm Si spacer-layer, a 17 nm thick Sb doped Si layer, and finally a 45 nm Si cap layer. The exact thicknesses were determined from a simulation of the dynamic x-ray diffraction data of this heterostructure. The main findings were: compared to bulk Si, the 2D electron mobilities in the Si1-yCy layer were clearly enhanced. The conduction band of Si1-yCy is indeed lowered with respect to that of Si, an effect that is mainly due to the biaxial tensile strain in the Si1-yCy layer. The mobilities in the 2D channel are, however, still limited by residual background impurities.

Selected references: [1], [2].

Surface Modifications in Strained-Layer Heteroepitaxy Studied by UHV Scanning Tunneling Microscopy

The growth of lattice-mismatched semiconductor heterostructures is of considerable importance for advanced microelectronic devices. Since the performance of these devices is strongly affected by structural defects such as misfit dislocations, the understanding and the control of strain relaxation are a critical issue for lattice mismatched heteroepitaxy. We have recently shown that the formation of misfit dislocations at the heterointerfaces leads to atomic scale changes of the surface structure of the epilayer, which are directly detectable by UHV scanning tunneling microscopy (STM) or even by atomic force microscopy (AFM). In the previous year we have shown experimentally that the formation of the interfacial dislocations produces atomic glide steps on the epitaxial surface. Therefore, the onset of strain relaxation as well as the degree of strain relaxation can be determined by STM.

In this year we have performed a quantitative scanning tunneling microscopy study of surface deformations induced by misfit dislocations formed during strained heteroepitaxy of the antiferromagnetic semiconductor EuTe on PbTe (111). Both compounds crystallize in the rocksalt structure with a lattice mismatch of 2.1%. The EuTe layer was grown by MBE on a PbTe buffer which was deposited on (111) BaF2 substrates. After interrupting the growth the samples were transferred to an attached UHV chamber, where the STM investigations were carried out.

According to the Matthews-Blakeslee mechanism, pre-existing threading dislocations form misfit segments at the EuTe/PbTe interface above the critical layer thickness. We observe pronounced surface deformations caused by single dislocations and dislocation reactions. The observed surface deformations exhibit a characteristic dependence on the orientation of the Burgers vector, which is in excellent quantitative agreement with calculations based on elasticity theory, taking into account the relaxation of the local strain fields due to the existence of a free surface. The use of the STM allows also for a study of the misfit dislocation reactions, even for dislocations located many monolayers below the epitaxial surface.

From our calculations we find that at the critical layer thickness about half of the total strain energy is locally relaxed by misfit dislocations. We have found direct experimental evidence that due to this local reduction of the strain energy, ridge-like structures are formed by stress-driven surface diffusion, which is a direct experimental evidence for a local dislocation-induced enhancement of the epitaxial growth.

Selected references: [3] - [9].

Fabrication of Si/SiGe Quantum Well Infrared Photodetectors

Detector elements were fabricated from MBE grown pseudomorphic Si/SiGe MQW structures by photolithography, reactive ion etching and metal-evaporation/lift-off techniques.

In 1995 the reactive ion etching facility in the clean room of the semiconductor physics building was modified to enable the use of gases like SF6 and CF4 for the reactive ion etching of the Si/SiGe structures.

A systematic study on the influence of the etch gas composition, its partial pressure (10 - 50 mbar), the mass flow (10 - 15 SCCM), the rf power (30 - 200 W) on the etching rates as well as on the side wall steepness of Si/SiGe microstructures has been made.

Concerning the side-wall steepness we observed a strong dependence on gas composition for similar plasma parameters. The admixture of oxygen to SF6 (mass flow ratio SF6:O2 5:1) improves the side-wall steepness considerably.

The MQW detector structures have typically lateral dimensions of 100 mm x 100 mm. The ratio of the Si-barrier width (20 - 30 nm) to the Si1-xGex well width (3 nm, with a Ge content x = 0.3) is so small that the difference between the etching rates for Si and SiGe is not relevant for the fabrication of these quantum well detectors.

Rather more important is the reproducibility of the etching depth (total depth: about 500 nm) within an accuracy of about 20 nm, which is required for contacting the lower buried highly p-doped bottom contact layer, which has a total thickness of 100 nm.

Selected references: [10], [11].

Damage in Reactive Ion Etched Nanostructures

Elastic strain present in reactive ion etched quantum wires and quantum dot structures as well as the side wall damage was investigated by high-resolution x-ray diffraction. From measurements of both the coherent as well as the diffusely scattered radiation not only information on the strain status of these nanostructures but also on the random elastic strain fields can be obtained.

We have investigated both III-V compound nanostructures (GaAs/AlAs) as well as II-VI compound structures (CdTe/MnTe, CdTe/CdZnTe, etc.). For the III-V compounds as etching gases SiCl4 and O2 were used for magnetically confined plasma etching. The II-VI compounds were reactively ion etched with a mixture of CH4 and H2.

The general findings are as follows: due to the patterning process, in quantum wires an elastic relaxation takes place. In addition, the reactive ion process induces an expansion of the mean lattice constant along the growth direction, both for III-V as well as for the II-VI compound heterostructures. These facts can be tentatively explained by the incorporation of chemical species into the sidewalls during the reactive ion etching process. In the II-VI nanostructures we found that annealing after the fabrication process reduces this additional expansion along the growth direction. In the latter case we attribute this behavior to the incorporation of H2 during the etching process and its outdiffusion during annealing.

The diffuse scattering is caused by random strains due to defects introduced by the fabrication process. From detailed simulations of the high resolution x-ray data it became apparent that the random strains, which cause the diffuse scattering (accompanying the coherent one), are caused by the fabrication process itself. In order to produce steep sidewalls, certain flow rates of e.g. SiCl4 and O2 (13.5 SCCM and 1.5 SCCM, respectively, at an operating pressure of 0.5 mTorr), microwave and r.f. powers (55 W and 35 W) turned out to be necessary. However, these etching conditions induce strain fields that extend nearly throughout the entire volume of dot-like structures with diameters of 300 nm and heights of about 2000 nm, as evidenced from the experimental data.

The x-ray diffraction analysis also reveals that after the reactive ion etching the nanostructures have a crystalline inner core the diameter of which is about 20 - 30% smaller than the apparent one as obtained from scanning electron microscopy. The outer layer is heavily distorted after the etching process, almost amorphous, which explains nicely the often reported discrepancy between, e.g., the photoluminescence yield of nanostructures and expectations based on the assumption of their geometrical shape.

Selected references: [12] - [15].

Fabrication and Optical Properties of CdTe/CdZnTe and ZnSe/ZnCdSe Quantum Wires and Dots by Nanolithography

With the advent of blue-green heterostructure lasers based on II-VI compounds it has become important to investigate optical properties of quantum wire and dot structures too, in order to evaluate attractive properties like a possible increase of oscillator strength and consequently lower laser thresholds in the nanostructures.

However, it is well known that the dry etching fabrication process induces defects, which seem to be less severe in II-VI compounds as compared to III-V compounds. In collaboration with two French groups in Grenoble and in Bagneux we have fabricated CdTe/CdZnTe and ZnSe/ZnCdSe wire and dot structures that were defined by electron beam lithography in France and etched by reactive ion etching (CH4 + H2) in Linz. Typical scanning electron microscopy images of these etched structures are shown in the relevant publications as cited below.

High density periodic patterns were written by e-beam nanolithography in a 150 nm thick polymethylmethacrylate resist layer. Arrays of 40x40 mm2 with wires and dots of different sizes were obtained. After deposition of a 40 nm titanium layer, a lift-off process was used to produce a metallic patterned mask on top of the sample. This pattern was transferred by reactive ion etching into the QW heterostructures.

A CH4/H2 gas mixture (1:8 volume ratio) at a pressure of 15 mTorr was used with a RF power of 180 W. The shape of the walls depends strongly on the II-VI material. Whereas for pure CdTe strong etching under the mask is observed, this is not the case for the selenide based QW structures.

The photoluminescence studies made on these structures include measurements of the PL efficiency and time resolved spectroscopy and reflect the crucial role of a damage layer induced by the etching process. This allows also to give quantitative data on the luminescence degradation in the smallest dry etched nanostructures.

The ZnSe based structures exhibit photoluminescence emission down to the smallest widths of 40 nm and 60 nm, respectively. The wider wires and dots of about 200 to 1000 nm show even an increase of the normalized photoluminescence intensity for the emission line in CdZnSe/ZnSe as compared to the unetched QW structure. With decreasing lateral size, the nanostructures first exhibit a red-shift of the emission line, which is attributed to the before-mentioned strain relaxation process. Further size reduction causes an apparent blue shift at about 70 nm lateral width. However, this width is still too large so that this spectral shift of the luminescence cannot be attributed to size quantization, which should become significant for less than 40 nm.

Selected references: [16] - [22].

In-situ Auger Electron Spectroscopy of MBE Grown II-VI Compound Epilayers

The GMe has supported an UHV tunnel between the MBE systems in the clean room in Linz. This tunnel has now been used for transferring samples from the MBE to a newly acquired Auger electron spectrometer, without the necessity for breaking the UHV. Thus nearly in situ investigations of near surface and buried layer regions can be made of MBE grown II-VI epilayers.

This Auger electron spectrometer has been used for the investigation of (001) oriented ZnS layers deposited on Silicon substrates, and for the structural and elemental analysis of ZnSe, CdSe, ZnTe and CdTe.

A particular advantage of the Auger electron spectrometer, namely the investigation of impurities on the surface of the MBE grown films (with the exception of oxygen and helium) has been used for surface related studies of binary and ternary II-VI compounds. With the scanning Auger spectrometer, a lateral resolution in the micrometer range can be achieved, which is advantageous for the detection of surface clusters as well as for island formation.

Ar-ion sputtering in combination with AES yields information on depth profiles of various elements, which is required for the analysis of II-VI compound multilayers.

The analysis of the line-shape of the AES spectra gives information on the chemical bonding of the analyzed atoms.

The Auger electron spectrometer has been used in particular for the investigation of the reactive ion etch process of II-VI compounds for which a mixture of CH4 and H2 is commonly used. The carbon and oxygen content at the etching front have been analyzed systematically. It turned out that carbon or oxygen penetration into the II-VI layers is minimized if the gas mixture for the reactive ion etching CH4 and H2 has a ratio of 1:6 to 1:8. This information is quite useful for minimizing the defect incorporation during the etching process.

Selected references: [23] - [26].

Acknowledgments

The work in the clean rooms in Linz has been further supported by several projects from the FWF, Vienna, Österreichische Nationalbank, Projektforschung des BMfWuF, ESPRIT basic research action UMIST.

References

[1] W. Faschinger, S. Zerlauth, G. Bauer, L. Palmetshofer: "Electrical properties of Si1xCx alloys and modulation doped Si/Si1-xCx/Si structures", Appl. Phys. Lett. 67, 3933 (1995).

[2] W. Faschinger, S. Zerlauth, J. Stangl, G. Bauer: "Molecular beam epitaxy of pseudomorphic Silicon/Carbon superlattices on Silicon substrates", Appl. Phys. Lett. 67, 2630 (1995).

[3] N. Frank, G. Springholz, G. Bauer: "Imaging of misfit dislocation formation in strained layer heteroepitaxy by ultra high vacuum scanning tunneling microscopy", Proceedings of the 22nd International Conference on the Physics of Semiconductors, Vancouver 1994, ed.: D.J. Lockwood. World Scientific Publishing, Singapore 1995, p. 652.

[4] N. Frank, G. Springholz, G. Bauer: "A novel method for the study of strain relaxation in lattice-mismatched heteroepitaxy: ultra-high vacuum scanning tunneling microscopy combined with in situ reflection high energy electron diffraction", J. Crystal Growth 150, 1190 (1995).

[5] G. Springholz, G. Bauer: "Systematic study of PbTe (111) molelular beam epitaxy using reflection high-energy electron diffraction intensity oscillations", J. Appl. Phys. 77, 540 (1995).

[6] J.H. Li, V. Holy, G. Bauer, J.F. Nützel, G. Abstreiter: "Investigation of strain relaxation of Ge1-xSix epilayers on Ge (001) by high-resolution x-ray reciprocal space mapping", Semicond. Sci. Technol. 10, 1621 (1995).

[7] G. Springholz: "Surface modifications due to strain relaxation in lattice-mismatched heteroepitaxy", Festkörperprobleme Vol. 35, 277 (1996).

[8] G. Springholz, N. Frank, G. Bauer: "The origin of surface roughening in lattice-mismatched Frank van der Merwe type heteroepitaxy", Thin Solid Films 267, 15 (1995).

[9] G. Springholz, N. Frank, G. Bauer: "Surface modifications in strained-layer heteroepitaxy studied by UHV-scanning tunneling microscopy", Solid State Electronics, in print.

[10] T. Fromherz, P. Kruck, M. Helm, G. Bauer, J.F. Nützel, G. Abstreiter: "Polarization dependence of intersubband absorption and photoconductivity in p-type SiGe quantum wells", Superlattices and Microstructures, submitted.

[11] T. Fromherz, P. Kruck, M. Helm, G. Bauer, J.F. Nützel, G. Abstreiter: "TM and TE polarized intersubband absorption and photoconductivity in p-typ SiGe quantum wells", Applied Physics Letters, submitted.

[12] A.A. Darhuber, E. Koppensteiner, G. Bauer, P.D. Wang, Y.P. Song, C.M. Sotomayor Torres, M.C. Holland: "X-ray reciprocal space-mapping of GaAs/AlAs quantum wires and quantum dots", Appl. Phys. Lett. 66, 947 (1995).

[13] H. Straub, G. Brunthaler, W. Faschinger, G. Bauer, C. Gourgon, L.S. Dang, H. Mariette, C. Vieu: "Photoluminescence of CdZnTe and CdZnSe quantum well wires fabricated by reactive ion etching", Materials Science Forum 182-184, 179 (1995), Trans Tech Publications, Switzerland.

[14] A.A. Darhuber, V. Holy, G. Bauer, P.D. Wang, Y.P. Song, C.M. Sotomayor Torres, M.C. Holland: "Cristalline and quasicristalline patterns in x-ray diffraction from periodic arrays of quantum dots", Europhysics Letters 32, 131 (1995).

[15] V. Holy, A.A. Darhuber, G. Bauer, P.D. Wang, Y.P. Song, C.M. Sotomayor Torres, M.C. Holland: "Elastic strains in GaAs/AlAs quantum dots studied by high resolution x-ray diffraction", Phys. Rev. B 52, 8348 (1995).

[16] A.A. Darhuber, H. Straub, S. Ferreira, W. Faschinger, E. Koppensteiner, G. Brunthaler, G. Bauer: "Structural investigation of II-VI compound semiconductor quantum wires using triple axis x-ray diffractometry", J. Crystal Growth 150, 775 (1995).

[17] A.A. Darhuber, H. Straub, S. Ferreira, W. Faschinger, H. Sitter, E. Koppensteiner, G. Brunthaler, G. Bauer: "Fabrication and x-ray diffractometry investigation of CdTe/MnTe multiple quantum wires", Materials Science Forum 182-184, 423 (1995), Trans Tech Publications, Switzerland.

[18] W. Faschinger: "Doping of wide gap II-VI compounds", J. Crystal Growth 146, 80 (1995).

[19] W. Faschinger, S. Ferreira, H. Sitter: "Band structure engineering and doping of wide gap II-VI superlattices", Appl. Phys. Lett. 66, 2516 (1995).

[20] W. Faschinger, S. Ferreira, H. Sitter: "Doping limitations in wide gap II-VI compounds by Fermi level pinning", J. Crystal Growth 151, 267 (1995).

[21] H. Mariette, C. Gourgon, L.S. Dang, J. Cibert, C. Vieu, G. Brunthaler, H. Straub, W. Faschinger, N. Pelekanos, W.W. Rühle: "Fabrication and optical properties of CdTe/CdZnTe quantum wires and dots processed by nanolithography", Semiconductor Heteroepitaxy: Growth, Characterization and Device Application, Ed. B. Gil and R.L. Aulombard, World Scientific, Singapore 1995, p. 383.

[22] H. Straub, G. Brunthaler, W. Faschinger, G. Bauer, C. Vieu: "Photoluminescence of CdZnSe/ZnSe quantum well structures fabricated by reactive ion etching", J. Crystal Growth., in print.

[23] E. Wirthl, H. Sitter, P. Bauer: "Monocristalline (100)-oriented ZnS Layers grown on Si by Molecular Beam Epitaxy", J. Cryst. Growth 146, 404 (1995).

[24] E. Wirthl, H. Straub, M. Schmid, H. Sitter, G. Brunthaler, P. Bauer: "AES-analysis of plasma-etched ZnSe", J. Crystal Growth, in print.

[25] E. Wirthl, M. Schmid, D. Stifter, H. Sitter, P. Bauer: "Auger Investigations on II-VI Ternary and Mulitnary Compounds", J. Cryst. Research and Technology, in print.

[26] E. Wirthl, H. Straub, H. Sitter, G. Brunthaler, M. Schmid, D. Stifter, P. Bauer: "AES Investigations on Plasma-etched II-VI Binary Compounds", Proc. Int. Symp. on Blue Laser and Light Emitting Diodes, Chiba, Japan 1996, Ohmsha Press, in print.

Project Information

Project Manager

Univ.-Prof. Dr. Günther BAUER

Institut für Halbleiterphysik, Johannes Kepler Universität Linz, A-4040 Linz, Austria

Project Group

Last Name      First Name     Status              Remarks                  

Bauer          Günther        Professor                                    

Schäffler      Friedrich      Professor                                    

Helm           Manfred        Univ.-Doz.                                   

Brunthaler     Gerhard        Ph.D.                                        

Faschinger     Wolfgang       Univ.-Doz.          until 30 August 1995     

Fromherz       Thomas         postdoc                                      

Darhuber       Anton A.       dissertation                                 

Kruck          Peter          dissertation                                 

Penn           Christian      dissertation                                 

Springholz     Gunther        postdoc                                      

Sitter         Helmut         Univ.-Doz.                                   

Wirthl         Edwin          dissertation                                 

Stifter        David          dissertation                                 

Pichler        Christian      diploma thesis                               

Ueta           Yukio          dissertation                                 

Wirtl          Elisabeth      technician                                   

Rabeder        Klaus          technician                                   

Schmid         Michael        diploma thesis                               

Kainz          Ursula         technician                                   

Stangl         Julian         dissertation                                 

Straub         Hubert         dissertation        50%GMe funding           

Zerlauth       Stefan         dissertation                                 

Publications in Reviewed Journals

1. A.A. Darhuber, G. Bauer, P.D. Wang, Y.P. Song, C.M. Sotomayor Torres, M.C. Holland: "Determination of the strain status of GaAs/AlAs quantum wires and quantum dots", Mat. Res. Soc. Symp. Proc. 358, 975 (1995).
2. A.A. Darhuber, E. Koppensteiner, G. Bauer, P.D. Wang, Y.P. Song, C.M. Sotomayor Torres, M.C. Holland: "X-ray reciprocal space-mapping of GaAs/AlAs quantum wires and quantum dots", Appl. Phys. Lett. 66, 947 (1995).
3. A.A. Darhuber, H. Straub, S. Ferreira, W. Faschinger, E. Koppensteiner, G. Brunthaler, G. Bauer: "Structural investigation of II-VI compound semiconductor quantum wires using triple axis x-ray diffractometry", J. Crystal Growth 150, 775 (1995).
4. A.A. Darhuber, H. Straub, S. Ferreira, W. Faschinger, H. Sitter, E. Koppensteiner, G. Brunthaler, G. Bauer: "Fabrication and x-ray diffractometry investigation of CdTe/MnTe multiple quantum wires", European Workshop on II-VI Semiconductors, Linz, Austria 1994; Materials Science Forum 182 - 184, 423 (1995), Trans Tech Publications, Switzerland.
5. A.A. Darhuber, E. Koppensteiner, G. Bauer, P.D. Wang, Y.P. Song, C.M. Sotomayor Torres, M.C. Holland: "Structural investigations of GaAs/AlAs quantum wires and quantum dots by x-ray reciprocal space mapping", Phys. D: Appl. Phys. 28, A 195 (1995).
6. R. Denecke, L. Ley, G. Springholz, G. Bauer: "Resonant photoemission studies of Pb1-xEuxTe", Proceedings of the 22nd International Conference on the Physics of Semiconductors, Vancouver 1994, ed.: D.J. Lockwood. World Scientific Publishing, Singapore 1995, p. 413.
7. W. Faschinger: "Doping of wide gap II-VI compounds", J. Crystal Growth 146, 80 (1995).
8. W. Faschinger: "Fundamental doping limits in wide gap II-VI compounds", Semiconductor Heteroepitaxy: Growth, Characterization and Device Applications, eds.: B. Gil, R.-L. Aulombard. World Scientific Publishing, Singapore 1995, p. 17.
9. W. Faschinger, S. Ferreira, H. Sitter: "Band structure engineering and doping of wide gap II-VI superlattices", Appl. Phys. Lett. 66, 2516 (1995).
10. W. Faschinger, S. Zerlauth, G. Bauer, L. Palmetshofer: "Electrical properties of Si1xCx alloys and modulation doped Si/Si1-xCx/Si structures", Appl. Phys. Lett. 67, 3933 (1995).
11. W. Faschinger, G. Brunthaler, R. Krump, A. Darhuber, S. Ferreira, H. Sitter: "MBE growth of heterostructures and superlattices containing MgTe", European Workshop on II-VI semiconductors, Linz, Austria 1994; Materials Science Forum Vols. 182 - 184, 407 (1995), Trans Tech Publications, Switzerland.
12. W. Faschinger, S. Ferreira, H. Sitter, R. Krump, G. Brunthaler: "Doping limits in wide gap II-VI semiconductors", Materials Science Forum Vols. 182 - 184, 29 (1995), Trans Tech Publications, Switzerland.
13. W. Faschinger, S. Ferreira, H. Sitter: "Doping limitations in wide gap II-VI compounds by Fermi level pinning", J. Crystal Growth 151, 267 (1995).
14. S. Ferreira, H. Sitter, R. Krump, W. Faschinger, G. Brunthaler, J.T. Sadowski: "Blue photoluminescence of Zn1-xCdxSe quantum wells in ZnMgSe", Semicond. Sci. Technol. 10, 489 (1995).
15. S. Ferreira, H. Sitter, W. Faschinger, R. Krump, G. Brunthaler: "Type I - type II band offset transition of the ZnMgSe-ZnTe system", J. Crystal Growth 146, 418 (1995).
16. S. Ferreira, H. Sitter, W. Faschinger: "Molecular beam epitaxy doping of ZnMgSe using ZnCl2", Appl. Phys. Lett. 66, 1518 (1995).
17. S. Ferreira, W. Faschinger, H. Sitter: "n-type doping of MBE grown ZnMgSe using ZnCl2", Materials Science Forum vols. 182 - 184, 77 (1995), Trans Tech Publications, Switzerland.
18. S. Ferreira, W. Faschinger, H. Sitter, R. Krump, G. Brunthaler, J.T. Sadowski: "Zn1xCdxSe quantum wells in ZnMgSe", European Workshop on II-VI Semiconductors, Linz, Austria 1994; Materials Science Forum Vols. 182 - 184, 195 (1995), Trans Tech Publications, Switzerland.
19. N. Frank, G. Springholz, G. Bauer: "Imaging of misfit dislocation formation in strained layer heteroepitaxy by ultra high vacuum scanning tunneling microscopy", Proceedings of the 22nd International Conference on the Physics of Semiconductors, Vancouver 1994, ed.: D.J. Lockwood. World Scientific Publishing, Singapore 1995, p. 652.
20. N. Frank, G. Springholz, G. Bauer: "A novel method for the study of strain relaxation in lattice-mismatched heteroepitaxy: ultra-high vacuum scanning tunneling microscopy combined with in situ reflection high energy electron diffraction", J. Crystal Growth 150, 1190 (1995).
21. R. Krump, S. Ferreira, W. Faschinger, G. Brunthaler, H. Sitter: "ZnMgSeTe light emitting diodes", Materials Science Forum vols. 182 - 184, 349 (1995), Trans Tech Publications, Switzerland.
22. G. Springholz: "Molecular beam epitaxy and structural properties of PbTe/EuTe short period superlattices", Materials Science Forum 182 - 184, 573 (1995), Trans Tech Publications, Switzerland.
23. G. Springholz, G. Bauer: "Systematic study of PbTe (111) molelular beam epitaxy using reflection high-energy electron diffraction intensity oscillations", J. Appl. Phys. 77, 540 (1995).
24. H. Straub, G. Brunthaler, W. Faschinger, G. Bauer, C. Gourgon, L.S. Dang, H. Mariette, C. Vieu: "Photoluminescence of CdZnTe and CdZnSe quantum well wires fabricated by reactive ion etching", Materials Science Forum 182 - 184, 179 (1995), Trans Tech Publications, Switzerland.
25. G. Bauer, M. Kriechbaum, Z. Shi, M. Tacke: "IV-VI quantum wells for infrared lasers", International Journal of Nonlinear Optical Physics and Materials 4, 283 (1995).
26. G. Grabecki, S. Takeyama, S. Adachi, Y. Takagi, T. Dietl, E. Kaminska, A. Piotrowska, E. Papis, N. Frank, G. Bauer: "Mesoscopic phenomena in microstructures of IV-VI epilayers", Jap. J. Appl. Phys. 34, 4433 (1995).
27. A.A. Darhuber, V. Holy, G. Bauer, P.D. Wang, Y.P. Song, C.M. Sotomayor Torres, M.C. Holland: "Cristalline and quasicristalline patterns in x-ray diffraction from periodic arrays of quantum dots", Europhysics Letters 32, 131 (1995).
28. V. Holy, A.A. Darhuber, G. Bauer, P.D. Wang, Y.P. Song, C.M. Sotomayor Torres, M.C. Holland: "Elastic strains in GaAs/AlAs quantum dots studied by high resolution x-ray diffraction", Phys. Rev. B 52, 8348 (1995).
29. G. Grabecki, S. Takeyama, S. Adachi, Y. Takagi, T. Dietl, E. Kaminska, A. Piotrowska, E. Papis, N. Frank, G. Bauer: "Conductance fluctuations in PbSe: Manifestation of ballistic transport in macroscale", Acta Physica Polonica A 88, 425 (1995).
30. W. Faschinger, S. Zerlauth, J. Stangl, G. Bauer: "Molecular beam epitaxy of pseudomorphic Silicon/Carbon superlattices on Silicon substrates", Appl. Phys. Lett. 67, 2630 (1995).
31. W.M. Plotz, E. Koppensteiner, H. Kibbel, H. Presting, G. Bauer, K. Lischka: "An investigation of x-ray reflectivity and -diffraction from electroluminescent short period Si-Ge superlattice structures", Semicond. Sci. Technol. 10, 1614 (1995).
32. J.H. Li, V. Holy, G. Bauer, J.F. Nützel, G. Abstreiter: "Investigation of strain relaxation of Ge1-xSix epilayers on Ge (001) by high-resolution x-ray reciprocal space mapping", Semicond. Sci. Technol. 10, 1621 (1995).
33. F. Geist, H. Pascher, N. Frank, G. Bauer: "Interband magnetotransmission and coherent Raman spectroscopy of spin transitions in diluted magnetic Pb1-xMnxSe", Phys. Rev. B 53, (15 Feb. 96).
34. G. Springholz: "Surface modifications due to strain relaxation in lattice-mismatched heteroepitaxy", Festkörperprobleme Vol. 35, 277 (1996).
35. G. Brunthaler, G. Bauer, G. Braithwaite, N.L. Mattey, P. Philips, E.H.C. Parker, T.E. Whall: "Hot carrier transport in SiGe/Si two-dimensional hole gases", Proceedings of the International Conference on Hot Carriers in Semiconductors, in print.
36. G. Brunthaler, H. Straub, W. Faschinger, G. Bauer: "Herstellung von II-VI Quantendrähten mit optischer Emission im blauen Spektralbereich", Seminar Grundlagen und Technologie elektronischer Bauelemente, 5.4. - 8.4.1995, Großarl, Österreich.
37. W. Faschinger: "Fundamental doping limits in wide gap II-VI compounds", World Scientific Publishing, in print.
38. W. Faschinger: "Fundamental doping limits in wide gap II-VI compounds", J. Cryst. Growth, in print.
39. S. Ferreira, H. Sitter, R. Krump, W. Faschinger, G. Brunthaler: "Room temperature blue electroluminescence from the ZnMgCdSe quaternary system", Submitted to J. Crystal Growth.
40. W. Hilber, M. Helm, F.M. Peeters, K. Alavi, R.N. Pathak: "Study of the impurity band and the magnetic field induced metal-insulator transition in a doped GaAs/ AlGaAs superlattice", Phys. Rev. B, in print.
41. H. Mariette, C. Gourgon, L.S. Dang, J. Cibert, C. Vieu, G. Brunthaler, H. Straub, W. Faschinger, N. Pelekanos, W.W. Rühle: "Fabrication and optical properties of CdTe/CdZnTe quantum wires and dots processed by nanolithography", Semiconductor Heteroepitaxy: Growth, Characterization and Device Application, Ed. B. Gil and R.L. Aulombard, World Scientific, Singapore 1995, p. 383.
42. C. Pichler, G. Springholz, G. Bauer: "A comparison of experimental resolution for critical thickness determination by UHV-STM, x-ray diffraction and in situ RHEED", Semiconductor Heteroepitaxy: Growth, Characterization and Device Application, Ed. B. Gil and R.L. Aulombard, World Scientific, Singapore 1995, p. 222.
43. G. Springholz, G. Bauer: "A scanning tunneling microscopy study of surface modifications induced by misfit dislocation formation in strained layer hetereoepitaxy", Applied Surface Science, submitted.
44. G. Springholz, N. Frank, G. Bauer: "The origin of surface roughening in lattice-mismatched Frank van der Merwe type heteroepitaxy", Thin Solid Films 267, 15 (1995).
45. G. Springholz, N. Frank, G. Bauer: "Surface modifications in strained-layer heteroepitaxy studied by UHV-scanning tunneling microscopy", Solid State Electronics, in print.
46. H. Straub, G. Brunthaler, W. Faschinger, G. Bauer, C. Vieu: "Photoluminescence of CdZnSe/ZnSe quantum well structures fabricated by reactive ion etching", J. Crystal Growth, in print.
47. E. Wirthl, H. Straub, M. Schmid, H. Sitter, G. Brunthaler, P. Bauer: "AES-analysis of plasma-etched ZnSe", J. Crystal Growth, in print.
48. J.H. Li, G. Bauer, L. Vanzetti, L. Sorba, A. Franciosi: "Strain and structural characterization of Zn1-xCdxSe laser structures grown on GaAs and InGaAs (001) substrates", J. Appl. Phys., submitted.
49. G. Bauer, J.H. Li, V. Holy: "High resolution x-ray reciprocal space mapping", Acta Physica Polonica, in print.
50. A.A. Darhuber, V. Holy, G. Bauer, P.D. Wang, Y.P. Song, C.M. Sotomayor Torres, M.C. Holland: "Quantitative analysis of elastic strains in GaAs/AlAs quantum dots", Physica B, submitted.
51. G. Hendorfer, W. Jantsch, W. Helzel, J.H. Li, Z. Wilamowski, T. Widmer, D. Schikora, K. Lischka: "Strain characterization of Hg1-xFexSe-layers by electron spin resonance", Mater. Sci. Forum, in print.
52. T. Fromherz, P. Kruck, M. Helm, G. Bauer, J.F. Nützel, G. Abstreiter: "Polarization dependence of intersubband absorption and photoconductivity in p-type SiGe quantum wells", Superlattices and Microstructures, submitted.
53. G. Bauer, A. Darhuber, V. Holy: "Structural characterization of reactive ion etched semiconductor nanostructures using x-ray reciprocal space mapping", Mat. Res. Soc. Symp. Proc., in print.
54. G. Springholz, G. Bauer, V. Holy: "Direct observation of stress driven surface diffusion due to localized strain fields of misfit dislocations in heteroepitaxy", Surface Science, in print.
55. M. Shima, L. Salamanca-Riba, G. Springholz, G. Bauer: "Double periodicity formation in EuTe/PbTe superlattices", Mat. Res. Soc. Symp. Proc., in print.
56. E. Wirthl, H. Sitter, P. Bauer: "Monocristalline (100)-oriented ZnS Layers grown on Si by Molecular Beam Epitaxy", J. Cryst. Growth 146, 404 (1995).
57. E. Wirthl, M. Schmid, D. Stifter, H. Sitter, P. Bauer: "Auger Investigations on II-VI Ternary and Mulitnary Compounds", J. Cryst. Research and Technology, in print.
58. E. Wirthl, H. Straub, H. Sitter, G. Brunthaler, M. Schmid, D. Stifter, P. Bauer: "AES Investigations on Plasma-etched II-VI Binary Compounds", Proc. Int. Symp. on Blue Laser and Light Emitting Diodes, Chiba, Japan 1996, Ohmsha Press, in print.
59. T. Fromherz, P. Kruck, M. Helm, G. Bauer, J.F. Nützel, G. Abstreiter: "TM and TE polarized intersubband absorption and photoconductivity in p-typ SiGe quantum wells", Applied Physics Letters, submitted.

Presentations

Invited Talks

1. G. Bauer, A.A. Darhuber, V. Holy: "Structural characterization of reactive ion etched semiconductor nanostructures using x-ray reciprocal space mapping", Materials Research Society 1995 Fall Meeting, Boston, MA, 27.Nov. - 1.Dez. 1995.
2. T. Fromherz, P. Kruck, M. Helm, G. Bauer, J.F. Nützel, G. Abstreiter: "Polarization dependence of intersubband absorption and photoconductivity in p-type SiGe quantum wells", International Conference on Intersubband Transitions in Quantum Wells: Physics and Applications, Oct.23 - 26, 1995, Kibbutz Ginosar (Sea of Galilee), Israel.
3. G. Bauer, J.H. Li, V. Holy: "X-ray reciprocal space mapping: new developments for precise information on strain in heteroepitaxy", 2nd Symposium on Physics in Material Science, Jaszowiec, Polen, 17. - 22. Sept. 1995.
4. W. Faschinger: "Fundamental doping limits in wide gap II-VI compounds", 7th International Conference on II-VI Compounds and Devices, Edinburgh, August 13 - 18, 1995.
5. G. Brunthaler, G. Stöger, A. Prinz, C. Penn, G. Bauer: "Beeinflussung der elektronischen Eigenschaften von Halbleiterheterostrukturen durch störstelleninduzierte Unordnung", Fachausschuß für Festkörperphysik der Jahrestagung der ÖPG, Leoben, Sept. 1995.
6. M. Helm: "Infrarotspektroskopie von Löchern in Si/SiGe Quantum Wells / Intersubbandrelaxation in GaAs/AlGaAs Quantum Wells", Universität Marburg, 28.11.1995.
7. M. Helm, W. Hilber, P. Kruck, T. Fromherz, M. Seto, G. Bauer: "Intersubbandübergänge in Halbleiter-Quantentöpfen und -Übergittern", Fachausschuß für Festkörperphysik, Jahrestagung der ÖPG, Leoben, Sept. 1995.
8. G. Bauer, N. Frank, G. Springholz: "Misfit dislocation formation in heteroepitaxy observed by UHV-STM", Workshop on interface structure and electronic transport properties of heterostructures, University of Minnesota, Minneapolis, USA, 4. - 6. Mai 1995.
9. G. Bauer, J.H. Li, E. Koppensteiner: "X-ray reciprocal space mapping of Si/SiGe heterostructures", European Materials Research Society, Strasbourg, France, 22. - 26. Mai 1995.
10. G. Bauer: "UHV-STM investigations of EuTe epitaxial layers", Physik-Kolloquium, Masaryk Universität Brünn, Tschechien, 7. Juni 1995.
11. G. Bauer: "Semimagnetic semiconductor heterostructures and superlattices", DPG Frühjahrstagung Berlin, 20. - 24. März 1995.
12. A. Darhuber, V. Holy, G. Bauer: "Quantitative analysis of elastic strains in GaAs/AlAs quantum dots", 3rd International Symposium on New Phenomena in Mesoscopic Structures, Mauii, Hawaii, 4. - 8. Dez. 1995.
13. T. Fromherz, J.H. Li, P. Kruck, M. Helm, G. Bauer: "Intersubband spectroscopy on Si/SiGe multi quantum wells and their structural characterization", Heterostructures de semiconducteurs IV-VI, Orsay, 26. - 27. Okt. 1995.
14. G. Bauer, A.A. Darhuber, V. Holy, J.H. Li: "X-ray diffraction on two-, one- and zero-dimensional structures", Heterostructures in Science and Technology (W.C. Röntgen 100 year anniversary), Universität Würzburg, 13. - 17. März 1995.
15. G. Springholz, N. Frank, G. Bauer: "Surface modifications due to strain relaxation in lattice-mismatched heteroepitaxy", Frühjahrstagung der Deutschen Physikalischen Gesellschaft, Berlin, 20. - 24. März 1995.

Conference Presentations

1. H. Straub, G. Brunthaler, W. Faschinger, G. Bauer, C. Vieu: "Photoluminescence of CdZnSe/ZnSe quantum well structures fabricated by reactive ion etching", 7th International Conference on II-VI Compounds and Devices, Edinburgh, UK 1995.
2. J.H. Li, V. Holy, G. Bauer, M. Hohnisch, H.-J. Herzog, F. Schäffler: "Strain relaxation and misfit dislocations in compositionally graded Si1-xGex layers on Si (001)", E-MRS Strasbourg 1995.
3. C. Pichler, G. Springholz, G. Bauer: "A comparison of experimental resolution for critical thickness determination by UHV-STM, x-ray diffraction and in situ RHEED", International Conference on Semiconductor Heteroepitaxy, Montpellier, France 1995.
4. G. Springholz, N. Frank, G. Bauer: "Surface modifications in strained-layer heteroepitaxy studied by UHV-scanning tunneling microscopy", 7th International Conference on Modulated semiconductor Structures, Madrid, Spain, July 10 - 14, 1995.
5. S. Ferreira, H. Sitter, R. Krump, W. Faschinger, G. Brunthaler: "Room temperature blue electroluminescence from the ZnMgCdSe quaternary system", 7th International Conference on II-VI Compounds and Devices, Edinburgh, August 13 - 18, 1995.
6. G. Brunthaler, H. Straub, W. Faschinger, G. Bauer: "Herstellung von II-VI Quantendrähten mit optischer Emission im blauen Spektralbereich", Seminar Grundlagen und Technologie elektronischer Bauelemente, 5. - 8.4.1995, Großarl, Österreich.
7. F. Geist, H. Pascher, G. Springholz, G. Bauer: "Band and exchange parameters of Pb1-xEuxTe", 7th International Conference on Narrow Gap Semiconductors, Santa Fe, New Mexico, Jan. 8 - 12, 1995.
8. H. Mariette, C. Gourgon, L.S. Dang, J. Cibert, C. Vieu, G. Brunthaler, H. Straub, W. Faschinger, N. Pelekanos, W.W. Rühle: "Fabrication and optical properties of CdTe/CdZnTe quantum wires and dots processed by nanolithography", International Conference on Semiconductor Heterostructures, Montpellier 1995.
9. G. Springholz, G. Bauer: "Study of misfit-dislocation formation in strained-layer heteroepitaxy using UHV-scanning tunneling microscopy", 7th International Conference on Modulated Semiconductor Structures, Madrid, Spain, July 10 - 14, 1995.
10. G. Springholz, G. Bauer: "A scanning tunnelling microscopy study of surface modifications induced by misfit dislocation formation in strained layer heteroepitaxy", Intenational Conference on the Formation of Semiconductor Interfaces, Princeton, USA, 1995.
11. G. Springholz: "Surface deformation induced by local strain fields of misfit dislocations studied by UHV-scanning tunnelling microscopy", Workshop on Molecular Beam Epitaxy, Max-Planck-Institut für Festkörperforschung, Stuttgart, 8. - 11. Okt. 1995.
12. E. Wirthl, H. Straub, M. Schmid, H. Sitter, G. Brunthaler, P. Bauer: "AES-analysis of plasma-etched ZnSe", 7th International Conference on II-VI Compounds and Devices, Edinburgh, UK 1995.
13. G. Springholz, G. Bauer: "A scanning tunnelling microscopy study of surface modifications induced by misfit dislocation formation in strained layer heteroepitaxy", Intenational Conference on the Formation of Semiconductor Interfaces, Princeton, USA 1995.
14. G. Springholz: "Surface deformation induced by local strain fields of misfit dislocations studied by UHV-scanning tunnelling microscopy", Workshop on Molecular Beam Epitaxy, Max-Planck-Institut für Festkörperforschung, Stuttgart, 8. - 11. Okt. 1995.
15. E. Wirthl, H. Straub, M. Schmid, H. Sitter, G. Brunthaler, P. Bauer: "AES-analysis of plasma-etched ZnSe", 7th International Conference on II-VI Compounds and Devices, Edinburgh, UK 1995.
16. W. Heiss, E. Gornik, C.R. Pidgeon, B.N. Murdin, C.J.G.M. Langerak, M. Helm, H. Hertle, F. Schäffler: "Intersubband lifetimes in Si/SiGe and GaAs/AlGaAs quantum wells", 7th International Conference on Modulated Semiconductor Structures, Madrid, Spain, July 1995.
17. A.A. Darhuber, G. Bauer, P.D. Wang, Y.P. Song, C.M. Sotomayor Torres, M.C. Holland: "Elastic strains in GaAs/AlAs quantum dots studied by high-resolution x-ray diffraction", 7th International Conference on Modulated semiconductor Structures, Madrid, Spain, July 10 - 14, 1995.
18. W. Faschinger: "Doping and Compensation in Wide Gap II-VI Semiconductors", International Conference on Semiconductor Heteroepitaxy, Montpellier 1995.
19. H. Straub, G. Brunthaler, W. Faschinger, G. Bauer, C. Gourgon, LeSi Dang, H. Mariette, C. Vieu: "Photoluminescence of CdZnSe quantum well wire structures fabricated by reactive ion etching"; 7th International Conference on II-VI Compounds and Devices, Edinburgh, August 13 - 18, 1995.
20. E. Wirthl, M. Schmid, D. Stifter, H. Sitter, P. Bauer: "Auger Investigations on II-VI Ternary and Mulitnary Compounds", 10th Int. Conf. on Ternary and Multinary Compounds, Stuttgart 1995.
21. E. Wirthl, H. Straub, H. Sitter, G. Brunthaler, M. Schmid, D. Stifter, P. Bauer: "AES Investigations on Plasma-etched II-VI Binary Compounds", Int. Symposium on Blue Laser and Light Emitting Diodes, Chiba, Japan 1996.
22. E. Wirthl, H. Sitter, P. Bauer: "Auger-Elektronenspektroskopie an II-VI-Verbindungshalbleitern", Fortbildungsseminar der GMe in Großarl

Doctor's Theses

1. G. Stöger, Quantum interference effects, hot electrons and metal insulator transition in Si/SiGe heterostructures and superlattices, Universität Linz, 1995.
2. E. Wirthl, Quantitative Auger-Analyse an binären und ternären II-VI Verbindungshalbleitern, Universität Linz, 1995.

Habilitations

1. Wolfgang Faschinger, Molekularstrahlepitaxie von II-VI Verbindungen mit großer Energielücke, Universität Linz, 1995.

Cooperations

1. Walter Schottky Institut, TU München, Garching
2. Nanoelectronics Research Center, Glasgow, Scotland
3. Institut für Festkörperelektronik, TU Wien
4. Experimentalphysik, Universität Bayreuth, Deutschland
5. Institute of Physics, Polish Academy of Sciences, Warsaw
6. Department of Physics, Heriot Watt University, Edinburgh, Scotland
7. ESRF, Grenoble, France
8. CEA-CNRS Grenoble, France
9. NIST-Reactor Radiation Division, Gaithersburg, MD, USA
10. Department of Physics, Purdue University, West Lafayette, IN, USA
11. Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
12. Institut für Experimentalphysik (Abteilung Atom-und Kernphysik), Universität Linz
13. University of Warwick, Coventry, England
14. Fraunhofer Institut, Freiburg, Deutschland
15. IBM Watson Research Center, Yorktown Heights, USA
16. Daimler Benz Laboratorien Ulm, Deutschland
17. Fachbereich Physik, Universität Paderborn, Deutschland