MBE conditions to obtain three Te-precursor surfaces for CdTe growth on (100) GaAs substrate and their detailed XPS studies are reported : one GaAs (6x1)100-Te reconstructed surface leading to (100) growth and two reconstructed surfaces, a (6x1)111 and a so-called (I3x3), both inducing a (111) growth. These surfaces have been characterized by the relative concentrations of three Te-adsorbed states TeAS, TeGa and TeTe which are defined by their XPS lines at 573.1, 572.5 and 572.2 eV and assigned to Te bound to As, Te bound to Ga and Te-bridges respectively. Such assignments serve as elements to discuss on a model for the heteroepitaxial growth of CdTe on a GaAs (100) substrate.

Liquid Phase Epitaxy (LPE) has been successfully employed to grow GaAs selectively on GaAs-coated Si which was previously prepared by Molecular Beam Epitaxy (MBE). A defect density reduction of more than two orders of magnitude compared to that in MBE layer was obtained. The growth was found to depend strongly on the mask pattern, and a marked difference between the growth on GaAs-coated Si and on pure GaAs substrates was observed. The growth may be explained in terms of the transport of the growing species from bulk of the melt to the substrate surface and the succeeding incorporation into the solid. The experimental results suggest that the transport process plays major roles in the growth on GaAs/Si substrates, while the surface reaction also contributes to the growth rate on GaAs substrate.

A detailed study of reflection high energy electron diffraction (RHEED) during growth of InxGai_xAs (0 < x 5_0.5) on GaAs was carried out. We focussed on the initial stages of growth where the growth is expected to be under coherent strain. RHEED studies provide us information on the growth front which is quite different from what is found in the lattice matched systems. In lattice matched systems, as the growth temperature is increased, the growth front becomes increasingly smooth (below congruent temperature) due to the enhanced surface kinetics. However, in the presence of strain we find that increased substrate temperature produces a growth front which is 3-dimensional in nature. This effect is explained by the reasoning that the equilibrium surface for the lattice matched systems are atomically smooth and that for a strained surface can be 3-dimensional depending upon surface strain.

The influence of the lattice mismatch strain on the growth mode and formation of defects is examined via computer simulations. Striking differences in the growth mode are suggested for compressive versus tensile strain in the overlayer. It is proposed and shown that the genesis of misfit induced defects is laid in the initial stages of growth at the coalescence boundaries of kinetically controlled clusters exceeding a critical size needed for epitaxical registry.

The surface stoichiometry of GaAs substrates influences considerably the initial stages of heteroepitaxy of II-VI compounds on (001)GaAs by molecular beam epitaxy. The growth mechanism of ZnSe has been investigated using a RHEED observation system, with which the intensity and half width of diffraction spots are measured. The growth mechanism of ZnSe on thermally cleaned substrates is the Stranski-Krastanov mode, while that on As-stabilized GaAs substrates is varied from the Stranski-Krastanov mode to the two-dimensional layer by layer growth mode with growth conditions of ZnSe. For Se rich conditions, which is characterized by a (2x1) reconstructed surface, the two-dimensional growth mode dominates, while for Zn-rich growth conditions, which is characterized by a c(2x2) reconstructed surface, the Stranski-Krastanov mode dominates.

The presence of a flat distribution of Gallium in a heteroepitaxial CdTe layer processed on GaAs, is originating from the disturbance of the upper layers of GaAs, due to the high lattice mismatch between CdTe and GaAs. A first order model, which considers the solid-state diffusion and the segregation effects at the outer surface of CdTe as the relevant mechanisms taking place during the process, provides this fairly constant Ga distribution through CdTe, and a step increase at the surface. The magnitude of the Ga density appears as a function of the growth rate and the process temperature. A more elaborated model would account also for the stress relaxation effects in the epilayer, allowing the diffusion constant to vary along CdTe.

In order to account for (100) and/or (111) oriented heteroepitaxial growth of CdTe on (100)GaAs, we have proposed a theoretical model based on the formation, during the early stage of the growth, of stable clusters of chemically bound tellurium atoms. In this model we consider not only geometrical features, but also the constraints for symmetries, bond - angles and bond-lengths associated with the growth of CdTe along the requested orientation. In analysing the applicability and the use of this model in more general cases, we are able to express, through lattice mismatch, relatively precise criteria for explaining and predicting possible regularities in the heteroepitaxial growth features on (100) surfaces of zinc blende crystal structures. As an example, it is explained why ZnTe, which is very similar to CdTe, is always (100) oriented on (100) GaAs and never (111). It is also shown why for ternary compounds the (111) oriented growth is obtained only for compositions x < 0,17 in the case of ZnxCdi-xTe on GaAs and x < 0,53 for MnxCdi-xTe-GaAs.

Molecular Mechanics and Monte Carlo Methods have been applied to the modelling of a heteroepitaxy of CdTe on GaAs presenting a lattice mismatch of 14.7%. The growth of one monolayer has been simulated. The model is restricted to the analysis of defect creation at points of high strain. Creation of stable and unstable defects have been observed from the beginning of the growth in the case of a "soft" substrate.

Thin (Hg,Cd)Te and CdTe films have been grown on GaAs (100) substrates respectively by organometallic vapor phase epitaxy and close-spaced vapor transport method. Electron microscopic observations have been carried out in order to characterize the crystallographic quality of the epitaxial layers. In the case of (100) epitaxial orientation, high resolution lattice images have revealed the presence of misfit dislocations, essentially Lomer dislocations, exactly located in the plane of the interface. When the growth of the epitaxial layer of CdTe has taken place in the <111> direction, the most visible defects are twins and microtwins present in the film near the interface.

Electrical and photoluminescence (PL) measurements of MBE-grown ZnSe films on GaAs substrates are reported as a function of growth temperature and post-annealing treatments in inert atmosphere. Isothermal and isochronal annealing of ZnSe indicate a reduction of free carrier concentration with post-annealing temperature > 400°C. From capacitance-voltage (C-V) profiling measurements, carrier concentration reduction is deduced to be a bulk effect. Concomitant with the loss of free carriers is a reduction of donor bound exciton intensity as observed from the low temperature PL measurements. Room temperature PL measurements on annealed gnSe show dominant deep level emission. Zinc selenide grown at elevated temperature (400 C) also reveals electrical and PL behavior similar to ZnSe subjected to post-annealing treatment at elevated temperature. The results are correlated with the formation of intrinsic defects compensating the unintentionally incorporated background donor impurities.

The results of a Monte Carlo simulation of crystal growth on the (001) face of diamond-structure semiconductors from the vapor phase are presented. The model shows that growth occurs by adatom clustering, cluster growth, and coalescence. The clusters are anisotropic on specular surfaces due to the influence of the symmetry of the surface reconstruction on diffusion. Anisotropic adatom motion is also shown to give rise to convolution of alternate step edges on terraced surfaces. The reconstruction is predicted to consist of large (2x1) domains on flat surfaces but small domains during growth at partial monolayer coverages. A short-range diffusion event is proposed to permit domain growth and reconstruction dimer alignment. Reconstruction domain formation and growth is predicted to produce oscillations in the half-order spots of reflection high-energy electron diffraction patterns.

A new method has been developed for the growth of graded band-gap Al_xGa_1-xAs alloys by molecular beam epitaxy which is based upon electron beam evaporation of the Group III elements. The metal evaporation rates are measured real-time and feedback controlled using beam flux sensors. The system is computer controlled which allows precise programming of the Ga and Al evaporation rates. The large dynamic response of the metal sources enables for the first time the synthesis of variable band-gap Al_xGa_1-xAs with arbitrary composition profiles. This new technique has been demonstrated in the growth of unipolar hot electron transistors, graded base bipolar transistors, and M-shaped barrier superlattices.

A new technique for lateral patterning of quantum well and superlattice semiconductor heterostructures has been investigated. The technique utilizes the lateral thickness variations exhibited by thin epitaxial films grown on nonplanar substrates, and the strong dependence of the confinement energy on the quantum well thickness in order to achieve lateral patterning of the effective bandgap and related physical properties. The growth of GaAs/A1GaAs quantum well heterostructures on nonplanar GaAs substrates using molecular beam epitaxy and organometallic chemical vapor deposition was characterized by transmission electron microscopy. Conditions for obtaining substantial lateral variations in the quantum well thickness have been identified. Novel semiconductor lasers whose performance relies on this patterning technique have been demonstrated. These devices exhibit new and improved features, including very low threshold currents (as low as 1.8 mA for uncoated devices at room temperature), and quantum-wire-like active regions.

Recent advances made in the heteroepitaxial growth led to a great deal of activity in the growth of GaAs based high speed devices in Si substrates. This is primarily caused by the possibility of utilization of the superior electrical and optical properties of GaAs and other III-V compounds and highly developed Si technology on Si substrates. However, there are still unresolved fundamental issues related to the material properties of polar/non-polar heteroepitaxy. Such issues are the effects of substrate tilting, in-situ and ex-situ annealing on the films (e.g. 3-D and 2-D nucleation, critical film thickness, etc.). A rigorous method is used to derive the equation of state of an interface formed between two bulk phases (metal-semiconductor, semiconductor-semiconductor) at a given temperature. The method is based on calculation of the effect of stresses and strains on properties of multilayered films grown on a thiCk substrate (flat and tilted). In the calculations, the total energy is minimized that gives explicit expressions for the interface properties (e.g. radius of the 3-D islands, critical film thickness, band offsets, Schottky barriers, etc.).

InAs1_xSbx materials are of great importance due to their potential of replacing HgCdTe material for the fabrication of infrared sources and detectors operating at wavelength 8-12 μm spectral range where the atmospheric absorption is minimum. Heteroepitaxial layers of InAsi_xSbx materials have been successfully prepared by molecular beam epitaxy (MBE) over the complete compositional range (0<x<1) on (100)InAs substrates. Details of the MBE system and the growth have been described elsewhere.1,2 Photoluminescence has been employed to characterize the material quality and explore the possibility of applications in optical sources. Band-edge photoluminescence peak wavelengths as long as 8 pm have been obtained for the first time among III-V compound semiconductor materials in spite of the existence of a large lattice mismatch up to N6.4%. These results are indicative of high quality material.

The use of tensile strain parallel to (100) interfaces in InAs xSb1-x strained-layer superlattices (SLSs) is a promising . technique for realizing III-V materials structures with small enough energy gap to achieve cutoff wavelength in excess of 12pm at 77K. These SLS materials have been grown by MBE using Sb2 and As, sources at substrate temperature of 425-450°C on InSb substrates with suitable intervening buffer layers. The entire epitaxial structure (buffer layers plus SLS) is in tension with respect to the thick InSb substrate, leading to extensive cracking of the material when conventional buffer layers are used. The cracking problem has been overcome by the initial growth of a severely mismatched buffer layer directly onto the InSb substrate. The resulting high level of strain induces the nucleation of enough dislocations to relieve much of the strain in the ensuing epitaxial layer, avoiding the accumulation of strain energy sufficient to form cracks. Subsequent grading layers are in compression and cracking does not occur. InAs 1Sb 9/InAs 3Sb7 SLSs grown on such buffers are crack-free and' 3shoc4 substantiai reduction in dislocation density relative to that in the buffer layers. FTIR measurements show substantial absorption at wavelengths beyond the cutoff wavelength for bulk InAsSb alloys.

Epitaxial thin layer marcury-cadmium telluride has recently become the most widely used infrared ckector material. For epitaxial growth, cadmium telluride is usually used as a substrate(1). Unfortunately, bulk cadmium telluride tends to twin, therefore large single crystals are difficult and expensive to preparA, It is hoped that GaAs with a CdTe buffer layer will be suitable for use as a substrate(2). We have investigated (111) CdTe growth on B facet of (111) GaAs by hot-wall epitaxy and evaluated the quality of the wafer. In this paper, first the introduction of the main feature of hot-wall epitaxial growth is shown. Next, the growth conditions of CdTe on GaAs is denoted. After presenting the evaluation results, this paper is summarized.

The Close Spaced Vapor Transport has been applied to the growth of ZnSe thin layers on (100) GaAs substrates. After a presentation of the technique involved in the growth, scanning electron microscopy and X-rays diffractometry studies show that the deposit is mainly cubic ZnSe with a slight contribution of hexagonal ZnSe. The influence of the deposition conditions on the growth rate is reported, and the two existing models are presented.

Reactive close spaced vapor transport in hydrogen has been used to deposit II-VI compound semiconductors on (0001) sapphire substrates. The CdTe grown layer are (111) oriented with some twinning as clearly shown by Laue diffraction patterns. For a substrate at 500°C the growth process is three dimensional and in a coalescence regime leading to highly facetted and oriented pyramidal surfaces with a (111) growth axis. From the DDX measured value, 2000 arc-sec, one mights infer that the crystallinity is relatively poor. However FL spectra show near-band-edge and exciton emission lines with a linewidth of less 0.6 meV at 2K. Also n-type In-doped films have typically electron concentration of 10¹⁵ -10¹⁶ cm^-3 with mobilities of few hundreds cm2 V-1 5-1 at room temperature. The CdTe epilayers on GaAs (100) are either (111) or (100), or a (111) + (100) mixture.The layers have textured surfaces with pyramids. In the (111) oriented growth the basis of the pyramid is triangular with epitaxial relation CdTe (211)//GaAs (011). High resolution TEM studies reveal sharp interface. The as-grown layers are n type (1015 - 1017 cm^-3) with mobility at 300 K of 390 cm² V^-1 s^-1, and the P. spectra shows near-band-edge recombination with line-width of 1.5 meV at 2K. In relevance to I.R. focal plane array technology, heteroepitaxy of CdHgTe on GaAs is obtained by growing HgTe upon one layer of CdTe with a subsequent interdiffusion heat-treatment process. Hall mobilities of 5000 (room temperature) and 8000 (20K) cm2 V^-1 .5^-1 for (100) layers are measured.

Very recently, atomic layer epitaxy of II-VI compounds has attracted considerable attention 1-6), which includes investigations of initial stages of heteroepitaxy1,2), photoluminescence characterization 3,4), and RHEED intensity variations 5,6). From a preliminary investigation on structural quality of Zn-chalcogenide layers, it is suggested that ALE-grown materials at a low substrate temperature are of better quality than MBE-grown materials at the same substrate temprature1). In order to avoid interdiffusion at heterointerfaces of superlattice structures, low temperature growth is preferable. However, low temperature growth is not favorable for growth of good quality films in terms of PL characterization. In this paper, we have made PL characterization of Zn-chalcogenide layers grown by ALE at a temperature ranging from 150 - 250°C, which is much lower than the usual growth temperature of 300°C, in comparison with those grown by MBE at the same temperature. It is found that PL spectra of ALE films are dominated by excitonic emissions, while those of MBE grown films are dominated by deep level emissions, which suggests that a good quality film grows by ALE and that ALE films are better than MBE ones in terms of PL characterization. Furthermore, we have investigated surface processes associated with ALE growth on the substrate by observing RHEED intensity variations.

Recently, several crystalline organic semiconductors have been found to form rectifying heterojunctions when deposited onto inorganic semiconductor substrates. In this paper, we discuss the growth and characterization of these organic-on-inorganic (0I) heterostructures. Both the purification of organic materials, and the fabrication procedures for OI heterostructures are described in detail. The electrical properties, as well as the microstructure of the organic material are found to be very sensitive to the deposition conditions. The valence band discontinuity at the OI heterojunction is measured for the first time, using both forward current-voltage characteristics and internal photo-emission. The interface state densities have been studied for several different organic semiconductors deposited on p-Si substrates. A model is proposed to account for the observed results.

We report the successful growth of tilted superlattices (TSLs) obtained by molecular beam epitaxy (MBE) deposition of fractional monolayer superlattices, (GaAs)m(AlAs)n, (m,n < 1), on vicinal (001) GaAs substrates. In these structures, the tilt angle of the TSL interfaces with respect to the (001) orientation and the TSL period may be adjusted Independently by choosing the values of m + n and the mis-orientation angle of the vicinal substrate plane. The TSL permits the control of a second dimension in crystal growth and offers a wealth of new opportunities for devices and structures. We present the analysis of several TSL structures by transmission electron microscopy (TEM) and low temperature cathodoluminescence (CL). The experimental results confirm that growth conditions on vicinal (001) surfaces can be selected to assure that growth proceeds as layer-by-layer step propagation with minimal island nucleation on the step terraces. Furthermore, the agreement with theory demonstrates directly the monoatomic nature of the surface steps. The power of this new growth technique is demonstrated by growing superlattices of quantum wire-like structures in a single growth.

Molecular beam epitaxy of structures associating alkaline-earth fluorides and semiconductors has received considerable attention in the last few years. In this paper, we review the results published paying special attention to structures associating Ca, Sr, Ba fluorides and Si, GaAs, InP semiconductors. General trends for fluoride/semiconductor growth behavior are emphasized, as well as the problems encountered in the growth of semiconductor/fluoride heterostructures.

In near future, heteroepitaxy of semiconductor on the insulator will be very important in the field of OEIC, 3D IC, high speed IC and so on. This paper presents a novel hetero-epitaxial growth of GaAs on CaF2 /Si substrate for such applications. First of all, a brief explanation about the features of group IIa fluorides(CaF2, SrF2, BaF2 and their mixed crystals) is made. Then, the experimental procedure and the effectiveness of the electron-beam exposure epitaxy(EBE-epitaxy) are described. It is shown that the EBE-epitaxy is potentially capable of growing a GaAs film having a smooth surface, good crystallinity and single crystallographic orientation. The discussion is also made to clarify the mechanism of the EBE-epitaxy.

We have developed a new technique for the realization of dielectric films (II-A fluorides and their mixtures) on corn-pound semiconductors. In this process, dielectric films are deposited in an e-beam system at room temperature and subsequently subjected to in-situ rapid isothermal annealing by using incoherent light sources incorporated in the e-beam system. In this paper, preliminary results of electrical and structural characteristics of CaF2 and CazSri-xF2 films on GaAs and InP are presented.

Low-energy (< 200 eV) ion irradiation during crystal growth from the vapor phase plays an important and sometimes dominant role in controlling the growth kinetics and physical properties of films deposited by glow discharge and ion beam sputter deposition, molecular beam epitaxy using accelerated dopants, and plasma-assisted chemical vapor deposition. Ion/surface interaction effects, including trapping, preferential sputtering collisional mixing, and surface segregation are used to interpret and model experimental results concerning the effects of low-energy particle bombardment on nucleation kinetics, growth kinetics, enhanced diffusion at interfaces, elemental incorporation probabilities, and dopant depth distributions. Of particular interest are the results of recent experiments designed to: (1) determine elemental incorporation probabilities and depth profiles of accelerated dopants in MBE Si and GaAs as a function of accelerated energy E and growth temperature Ts, (2) investigate nucleation and growth kinetics of In overlayers using primary-ion deposition as a function of EInand Ts on clean Si(100)2x1 surfaces, (3) use molecular dynamics and Monte Carlo simulations to investigate microstructure evolution, (4) investigate the role of low-energy ion irradiation in reducing dislocation densities in epitaxial TiN(100) layers, and (5) use low-energy ion-mixing to grow unique single-crystal metastable semiconducting alloys.

We have grown GaAs on Si (100) substrates misoriented 4° from the [110] direction using a KrF pulsed excimer laser-assisted Molecular Beam Epitaxy. In this work, we report the systematic study of 2000 A GaAs films grown on Si using a two step growth sequence. Raman scattering, Rayleigh scattering, near band edge photoluminescence, cross-sectional TEM microscopy, in situ RHEED, and optical surface roughness profiles are used to characterize the differences between laser irradiated and non-irradiated areas of the samples. We find a reduction of defects, an enhancement of photoluminescence intensity, and no evidence for laser-induced melting for power levels of up to 25 MW/cm². Photoluminescence linewidths at 4.5K are comparable to widths observed for 1 micrometer thick GaAs films grown on Si.