Atomic layer epitaxy (ALE) is not so much a new technique for the preparation of thin films as a novel modification to existing methods of vapor‐phase epitaxy, whether physical [e.g., evaporation, at one limit molecular‐beam epitaxy (MBE)] or chemical [e.g., chloride epitaxy or metalorganic chemical vapor deposition (MOCVD)]. It is a self‐regulatory process which, in its simplest form, produces one complete molecular layer of a compound per operational cycle, with a greater thickness being obtained by repeated cycling. There is no growth rate in ALE as in other crystal growth processes. So far ALE has been applied to rather few materials, but, in principle, it could have a quite general application. It has been used to prepare single‐crystal overlayers of CdTe, (Cd,Mn)Te, GaAs and AlAs, a number of polycrystalline films and highly efficient electroluminescent thin‐film displays based on ZnS:Mn. It could also offer particular advantages for the preparation of ultrathin films of precisely controlled thickne...

Atomic layer epitaxy

Introduction Properties of Semiconductors Introduction Crystallographic Properties Lattice Constants and Thermal Expansion Coefficients Elastic Properties Surface Free Energy Dislocations Planar Defects Problems References Heteroepitaxial Growth Introduction Vapor Phase Epitaxy (VPE) Molecular Beam Epitaxy (MBE) Silicon, Germanium, and Si1-xGex Alloys Silicon Carbide III-Arsenides, III-Phosphides, and III-Antimonides III-Nitrides II-VI Semiconductors Conclusion Problems References Surface and Chemical Considerations in Heteroepitaxy Introduction Surface Reconstructions Nucleation Growth Modes Nucleation Layers Surfactants in Heteroepitaxy Quantum Dots and Self-Assembly Problems References Mismatched Heteroepitaxial Growth and Strain Relaxation Introduction Pseudomorphic Growth and the Critical Layer Thickness Dislocation Sources Interactions between Misfit Dislocations Lattice Relaxation Mechanisms Quantitative Models for Lattice Relaxation Lattice Relaxation on Vicinal Substrates: Crystallographic Tilting of Heteroepitaxial Layers Lattice Relaxation in Graded Layers Lattice Relaxation in Superlattices and Multilayer Structures Dislocation Coalescence, Annihilation, and Removal in Relaxed Heteroepitaxial Layers Thermal Strain Cracking in Thick Films Problems References Characterization of Heteroepitaxial Layers Introduction X-Ray Diffraction Electron Diffraction Microscopy Crystallographic Etching Techniques Photoluminescence Growth Rate and Layer Thickness Composition and Strain Determination of Critical Layer Thickness Crystal Orientation Defect Types and Densities Multilayered Structures and Superlattices Growth Mode Problems References Defect Engineering in Heteroepitaxial Layers Introduction Buffer Layer Approaches Reduced Area Growth Using Patterned Substrates Patterning and Annealing Epitaxial Lateral Overgrowth (ELO) Pendeo-Epitaxy Nanoheteroepitaxy Planar Compliant Substrates Free-Standing Semiconductor Films Conclusion Problems References Appendix A: Bandgap Engineering Diagrams Appendix B: Lattice Constants and Coefficients of Thermal Expansion Appendix C: Elastic Constants Appendix D: Critical Layer Thickness Appendix E: Crystallographic Etches Appendix F: Tables for X-Ray Diffraction Index

Heteroepitaxy of Semiconductors: Theory, Growth, and Characterization

CdTe films have been grown on (100) GaAs substrates with two different epitaxial relations: (111)CdTe∥(100)GaAs and (100)CdTe∥(100)GaAs. High resolution electron microscope observation of these two types of interfaces was carried out in order to investigate the role of the substrate surface microstructure in determining which type of epitaxy occurs. The interface of the former type shows a direct contact between the CdTe and GaAs crystals, while the interface of the latter type has a very thin layer (∼10 A in thickness), which is most likely an oxide, between the two crystals. These observations suggest that the GaAs substrate preheating cycle prior to CdTe film growth is crucial in determining which type of epitaxy occurs in this system.

High resolution electron microscope study of epitaxial CdTe‐GaAs interfaces

CdTe-GaAs(100) interface: MBE growth, rheed and XPS characterization

In this letter we report the first growth of high‐quality, single crystal thin films of Cd1−xMnxTe; the films are deposited by molecular beam epitaxy. Cd1−xMnxTe is one of a newly developed class of magneto‐optic materials called diluted magnetic semiconductors. Films with mole fractions of up to 50% Mn have been grown with no indication of any MnTe phases. A sputtered Auger electron spectroscopy depth profile shows that the Mn is uniformly incorporated throughout the film.

Molecular beam epitaxy of Cd1−xMnxTe

Using the molecular beam epitaxial (MBE) technique, CdTe and Hg1-xCdxTe have been grown on Cr-doped GaAs (100) sub-strates A single effusion cell charged with polycrystal-line CdTe is used for the growth of CdTe films The CdTe films grown at 200 °C with a growth rate of ~ 2 μm/hr show both streaked and “Kikuchi” patterns, indicating single crystalline CdTe films are smoothly grown on the GaAs sub-strates A sharp emission peak is observed at near band-edge (7865 A, 1577 eV) in the photoluminescence spectrum at 77 K For the growth of Hg1-xCdxTe films, separate sources of HgTe, Cd and Te are used Hg06Cd04Te films are grown at 50 °C with a growth rate of 17 μm/hr The surfaces are mirror-smooth and the interfaces between the films and the substrates are very flat and smooth As-grown Hg06Cd04Te films are p-type and converted into n-type by annealing in Hg pressure Carrier concentration and Hall mobility of an annealed Hg06Cd04Te film are 1 × 1017 cm−3 and 1000 cm2/V-sec at 77 K, respectively

Molecular beam epitaxy of CdTe and Hg1-xCdxTe ON GaAs (100)

The epitaxial layers of Hg1−xCdxTe (0.17≦×≦0.3) were grown by liquid phase epitaxy on CdTe (111)A substrates using a conventional slider boat in the open tube H2 flow system. The as-grown layers have hole concentrations in the 1017− 1018 cm−3 range and Hall mobilities in the 100−500 cm2/Vs range for the x=0.2 layers. The surfaces of the layers are mirror-like and EMPA data of the layers show sharp compositional transition at the interface between the epitaxial layer and the substrate. The effects of annealing in Hg over-pressure on the properties of the as-grown layers were also investigated in the temperature range of 250−400 °C. By annealing at the temperature of 400 °C, a compositional change near the interface is observed. Contrary to this, without apparent compositional change, well-behaved n-type layers are obtained by annealing in the 250−300 °C temperature range. Sequential growth of double heterostructure, Hgl−xCdxTe/Hgl−yCdyTe on a CdTe (111)A substrate was also demonstrated.

Lpe growth of Hgl−xCdxTe using conventional slider boat and effects of annealing on properties of the epilayers

A systematic investigation has been performed on diffusion of Zn in n-type InSb using elemental Zn and Sb in closed ampoules at temperature range 355–455 °C. The diffusion behavior could be well understood by arranging the data as a function of the mole ratio of Sb to Zn in the source, Nsb/Nzn. The diffusion depth was constant, independing on the total amount of Zn or/and Sb source loaded into ampoule when Nsb/Nzn≤0.5 or Nsb/Nzn ≥5, if Zn source was enough. When Nsb/Nzn ≥5, a highly planar diffusion front and a high quality p-type layer were reproducibly obtained. However, when Nsb/Nzn ≤ 0.5, a very ragged diffusion front and much damage were observed. 3–5 μm InSb photovoltaic detector arrays with 8 elements were prepared using above results.

K. Nishitani

Papers

Molecular beam epitaxy of CdTe and Hg1-xCdxTe ON GaAs (100)

Lpe growth of Hgl−xCdxTe using conventional slider boat and effects of annealing on properties of the epilayers

Extremely reproducible zinc diffusion into InSb and its application to infrared detector array