Different samples originating from the same LEC ingot have been used in order to determine the variation of the EL2 concentration versus depth after different types of thermal annealing ( 450 and 850°C : the temperatures generally used in technological processes ). The annealing of EL2 near the surface at 850°C has been interpreted as the result of the deviation from the stoichiometry near the surface, due to [As] variation induced by vacancy diffusion. At 450°C, the annealing of EL2 can only be explained by the dissociation of a complex, followed by the migration of one of the constituants, confirming that the EL2 defect is the complex AsGa- Asi.

The effects of In doping on the structural properties of liquid phase epitaxially (LPE) grown GaAs layers are studied. The distribution coefficient of In in the GaAs at 800 ° C was determined to be 0.033 which was consistent with the value calculated from the pseudobinary phase diagram of the ternary system at a dilute In concentration. The full widths at halfmaximum (FWHM) of x-ray double crystal rocking curves show that a GaAs epi-layer of good crystalline quality can be obtained by doping In to a concentration up to 4.3 × 1019 cm−3, beyond which a sharp increase in the FWHM is observed. Etch pit density (EPD) measurement shows that the dislocation density is reduced by doping the epi-layer with In. At the optimal In concentration of 2.4 × 1019 cm−3, the EPD is reduced by a factor of 20 when measured at the surface of a 9 um thick epilayer.

Photoluminesce measurements made at 15 K show two sharp emission spectra near the bandedge. The relative intensities of the two emissions, I(l.49eV)/I(l.5eV) are reduced with increasing In content. This suggests that incorporation of Carbon acceptors is suppressed by In doping in the GaAs epilayers. The FWHM as small as 5 meV of the bandedge transition was obtained for the epi-layer doped with In concentration of 2.4 × 1019 cm−3.

We have developed a process to grow both undoped, semi-insulating (SI) and silicon-doped, semiconducting (SC) GaAs using a vertical Bridgman method. The technique combines advantages of both liquid encapsulated Czochralski (LEC) and horizontal Bridgman (HB) processes. SI ingots, grown in pBN boats, and SC ingots, grown in quartz boats, are passed through a relatively shallow temperature gradient. Properties of the resulting material are highly uniform across the surface of a wafer. Because of the small temperature gradient, dislocation densities are very low (typically under 4000/cm∩2).

EBER is a form of modulated reflectance spectroscopy in which a low energy electron beam alters the sample surface potential. For III-V semiconductors, the spectra are characteristic of electroreflectance, including excitonic, interband, and impurity transitions. The study of these transitions provides accurate estimations of band gaps in bulk and thick film samples. Measurements of the band gap energy in compounds such as AlxGa1-xAs provide highly precise evaluations of their composition.

Additionally, EBER spectra of quantum well structures and heterojunctions provide useful information about the composition and quality of materials and interfaces. For quantum wells, detected features suggest the presence of allowed, disallowed, and resonant states. In EBER spectra of HEMT structures, peaks are apparent resulting from transitions between the valence band and the states in which the electrons are confined. We present examples of EBER determination of AlGaAs composition, single GaAs/AlGaAs quantum well evaluation, and HEMT characterization.

Rapid Thermal Annealing (RTA) effects on generation or annihilation of deep levels in GaAs have been investigated by Deep Level Transient Spectroscopy (DLTS). Capping proximity technique using three annealing configurations are employed to anneal Liquid Encapsulated Czochralski (LEC) and Bridgman (B) substrates, or Vapor Phase Epitaxy (VPE) and Liquid Phase Epitaxy (LPE) layers. The RTA treatment is performed from 800 to 950°C for two annealing times ( 3 and 10s).

The DLTS data show that the evolution of the native defects depends on the GaAs growth method and also the annealing configuration. We observe the appearance of two new electron traps named RL1 and RL2 induced by the RTA process which depend on the kind of substrate: RL1 and RL2 are created in LEC material while only RL1 is detected in B material. A general comparison of our results with others reported in the literature show that these new electron traps are related to the change of stoichiometry at the GaAs surface and also depend on the existence of specific native defects in the starting GaAs material. It is proposed that the creation of RL1 is related to the EL6 native defect and discuss a possible physical origin for this level. We also propose that RL2 and EL5 originate from the same defect and suggest the divacancy VGaVAs as a possible origin for this trap.

We have studied the ternary (Ga, In)As layers in GaInAs/GaAs heterostructure systems after conventional furnace annealing or rapid thermal annealing (RTA). Measurement was done by the double crystal X-ray rocking curve technique (XRC) and the Auger Electron Spectroscopy technique (AES). X-ray rocking curves show an asymmetric shoulder in the GaInAs epilayer peak indicating a smaller lattice spacing near the surface. Epilayer peaks of encapsulated samples also show an asymmetric shoulder which is perhaps due to the tensile stress in the epilayer caused by the encapsulant film. AES depth profiles for 600°C, 15 minutes proximity annealed sample show that the concentrations of Ga, In, and As are not uniform over about 60 nm depth, showing a Garich and In, As-deficient surface. For 700°C, 20 seconds a RTA treated sample shows no such non-uniformity.

The metal-organic vapor phase epitaxy (MOVPE) technique is perhaps themost versatile of the conventional III–V growth epitaxial systems. This versatility stems from the wide variety of chemical precursors available for the growth and doping of the films. Two examples of this versatility, carbon doping and selective epitaxy, are presented. Future progress within this technology will continue to be driven by the development of new chemistries.

We have investigated the use of various alkylarsine compounds as alternatives to arsine in the metalorganic vapor phase epitaxy (MOVPE) of GaAs. These As-precursors, which include homologues of methyl, ethyl and butyl-based compounds, are typically low vapor pressure liquids and thus much safer to handle than arsine, which is a toxic high pressure gas. To enable a direct comparison of the alkylarsine and arsine sources, measurement of their growth and thermal decomposition properties were obtained in the same reactor under identical conditions. The composition and purity of the precursor compound was observed to affect both the film growth rate and its electrical and optical properties.

Epitaxial single crystal (001) chalcopyrite-structure ZnGeAs2 and single crystal (100) zinc blende-structure (ZnGeAs2)xGe1−x alloys have been grown by organometallic vapor phase epitaxy on (100) GaAs. Selected area electron diffraction was used to determine the crystal structure for several Zn:Ge molar flow ratios. Bulk chemical composition was determined by electron microprobe and correlated to crystal lattice constants obtained from x-ray diffraction. Due to the lattice mismatch between chalcopyrite-structure ZnGeAs2 and the GaAs substrate, the epitaxy is elastically strained, compressing the a-lattice constant and elongating the c-lattice constant. Optical absorption and transmission spectroscopy indicate the zinc-blende-structure material has an indirect band gap of approximately 0.6 eV, whereas the chalcopyrite ZnGeAs2 has a direct band gap of 1.15 eV. Secondary ion mass spectroscopy reveals significant Zn diffusion into the GaAs substrate if the Zn:Ge molar flow ratio exceeds the ratio required for stoichiometric chalcopyrite-structure crystal growth.

Atmospheric OMVPE has been used, with SiH4 as the dopant, to grow n+-GaAs with free-carrier levels upto about 9e18 cm−3. Following a steady rise in carrier concentration with dopant pressure, the carrier concentration is seen to fall rapidly with further doping. Hall-effect and quantitative SIMS data have been used to obtain the distribution of silicon onto donor and acceptor sites. It is seen that there is negligible compensation upto free-carrier levels of about 5e18 cm−3. The mechanism of compensation throughout the doping range is discussed.

Several properties of InSb such as high mobility and narrow bandgap make it an attractive candidate for many unique devices. We have examined the metalorganic chemical vapor deposition (MOCVD) of InSb on GaAs and InSb substrates under a variety of conditions using trimethylindium and trimethylantimony sources. The absolute metal-organic partial pressures above the susceptor were monitored using in-situ Ultraviolet (UV) absorption spectroscopy. X-ray studies of the homoepitaxial growth of InSb on InSb substrates (100) indicate good crystalline epitaxial growth while the x-ray peak for the InSb grown on GaAs (100) is broadened due to defects. Room-temperature Hall mobility measurements performed on the heteroepitaxial InSb layer on GaAs substrates indicates that the mobility of the InSb increases with increasing layer thickness. Mobilities range from 12,000 cm2/V sec for 0.8 micron layers to 38,000 cm2/V sec for 7.4 micron layers. The carrier concentrations are relatively constant (2 to 4 × 1016 cm−3 ) for the n type InSb deposited layers.

We have analyzed the redistribution parameters for InP grown by organometallic vapor phase epitaxy (OMVPE) on GaAs substrates. The layers, grown using (trimethyl Indium) TMIn at atmospheric pressure, have been characterized for epitaxial quality using photoluminescence, energy dispersed x-ray analysis, and optical microscopy. In order to better understand the effects of inter-diffusion and inter-mixing for the GaAs into the InP epitaxial layer, the layer-substrate interface was first probed by growing consecutive samples of InP for increasingly longer growth times, and thus characterizing the layers as one moves away from the interface. For more detailed analysis, cross-sections of the InP/GaAs interface were prepared for scanning transmission electron microscopy (STEM). Energy dispersed x-ray analysis has shown that all elements In, Ga, As, and P, are present on the epitaxial side of the interface, while only Ga and As are present on the substrate side. A combination of electron diffraction and luminescence measurements show the epitaxy is at least 80% InP at the interface and essentially 100% InP at a distance of 6000Å into the epilayer. Electron diffraction and bright field investigation at the interface show the existence of a second phase, existing in a mostly InP matrix. The effects of redistribution in heteroepitaxial InP/GaAs will be discussed.

The effect of the group V isoelectronic dopant antimony (Sb) on the optimum growth temperature for GaAs and AIGaAs MBE grown films is examined with the aim of producing heterostructures at the lowest possible temperatures. RHEED intensity oscillations have been used to quantify the incorporation rate of Ga, Al, and As for different growth temperatures. The electrical properties of the layers are characterized using photoluminescence spectroscopy (PL), Hall mobility measurements, and deep level transient spectroscopy (DLTS). Results show that isoelectronic Sb doping of GaAs and AIGaAs permits the growth of these materials at temperatures up to 800C lower than optimum, with deep level trap densities, photoluminescence quality, and Hall mobilities at least comparable or better than those films grown at optimal temperatures.

The control of p-type dopants is very important in producing high performance minority carrier devices such as heterojunction bipolar transistors (HBT) and lasers. In this study, an electrical characterization technique is described which is very sensitive to the p-type dopant profile in a heterojunction. Both the placement of the dopant, i.e. the as-grown profile, and thermal diffusion effects have been investigated. The factors which control the initial placement and subsequent diffusion of the dopant species have been determined and used to produce device-quality GaAs/Al0.30Ga0.70As p+/n heterojunctions.

Dissociation species produced by low-energy electron Irradiation of triethylgallium (TEGa) have been used as a carbon doping source during growth of GaAs by chemical beam epitaxy. Mass spectral analysis shows that TEGa dissociates at electron energies greater than 20 eV, and that the fragmentation pattern of TEGa consists of methyl radicals, ethyl radicals, and gallium compounds. In order to study the doping properties of carbon, carbon-doped GaAs films were grown under several conditions and were characterized by Hall measurements, photoluminecence spectrum, secondary Ion mass spectrometry, and double crystal X-ray diffraction. The hole carrier concentration could be varied up to ∼1020 cm−3, and the doping profile of carbon was well-controlled.

Reflectance-difference spectroscopy (RDS) is a recently developed optical technique that allows to monitor chemical and structural changes at a growing semiconductor surface, in-situ and in real-time. This technique was applied recently to organometallic chemical vapor deposition (OMCVD) on a [100] GaAs growth surface. The results show that submonolayer coverage of reacted species can be followed by this technique, which provided unique insights into the microscopic growth mechanisms. The time, temperature and pressure dependences of surface coverage show that OMCVD growth is controlled by two basic processes with distinct activation energies, i.e. reversible chemisorption (at -26 kcal/mole), and decomposition (at 39 kcal/mole) of trimethylgallium (TMG) at surface lattice sites. The importance of reversible chemisorption, which is of an excluded-volume type, due to the large size of the TMG molecule, had been overlooked until now in the literature, where only one activation energy was used to describe growth kinetics.

An experimental and theoretical study has been undertaken of the effects of natural and forced convection in horizontal epitaxial reactors. The epitaxial growth of GaAs was used as the experimental vehicle for this study. A mathematical model for mass, momentum and energy transfer in the reactor was developed. Excellent correlation between modeled and experimental results was demonstrated over a wide range of reactor pressures and susceptor geometries. Recirculation of hot gases, caused by natural convection, was found to result in a strong pressure dependence of growth rate at higher susceptor slopes. Low reactor pressures have been shown to be a more effective way to eliminate recirculation than high gas flow rates.

Electron diffraction and high resolution electron microscopy (HREM) have been used to investigate the origin of multiple orientation-relationships and defect structure of CdTe thin films grown on (100) GaAs and Si substrates by metal- organic chemical vapor deposition (MOCVD). It has been determined that growth at 370°C with pre-exposure of the GaAs surface to Te following oxide desorption treatment at 600°C resulted in non-parallel epitaxy ((111)CdTe // (100)GaAs), while growth at 300°C following oxide desorption at 500°C with no exposure to Te resulted in parallel epitaxy ((100)CdTe // (100)GaAs). Both epitaxial orientation-relationships were observed on the same substrate for growth at 300°C temperature after 600°C oxide desorption treatment, but with no pre-exposure of the GaAs surface to Te. Preliminary results of growth of CdTe on Si are also reported.

X-ray diffraction techniques were used to evaluate Cd1-yZnyTe grown on GaAs substrate orientations of {100}2°, {111}, {012}, and {123}. High-quality layers having compositions at or close to the CdTe and ZnTe binary end points can be grown on GaAs, but most of the ternary compositions have extremely broad rocking curves. Layers grown on {123} and {012} were found to have large tilts toward {111} about <121> that varied systematically with the lattice mismatch; this is consistent with the mismatch being accommodated by the formation of a low-angle tilt boundary at the interface. {111} layers were found to be twinned, and thus {100}2° and {123} appear to better suited for vapor-phase epitaxial growth (VPE). High-resolution x-ray diffractometer measurements showed that the lattice mismatch is almost entirely taken up by plastic deformation, and only a small tetragonal distortion was measured. CdTe was distorted more than ZnTe, and a greater distortion was measured for layers grown on {100}2° than on {111}, in agreement with estimates made using bulk elastic constants.

It is now common to claim the fabrication of heterointerfaces, which are atomically flat over distances in the micron range. However, when chemical lattice imaging and digital pattern recognition are combined to examine quantitatively individual semiconductor heterointerfaces of the highest quality, substantial atomic scale roughness is observed. In this paper we review the application of chemical imaging and pattern recogntion techniques to the characterisation of heterointerfaces at near-atomic resolution, and discuss the possible ways the results can be combined with optical measurements to give an overall picture of interfacial roughness.