The mixing of highly silicon-doped GaAs/AlAs superlattices as a result of annealing has been investigated by transmission electron microscopy and secondary ion mass spectrometry. As silicon doping-levels were raised in this study to 1019 cm−3 and 1020 cm−3 defects such as prismatic dislocation loops and Si-rich precipitates were observed to occur in the superlattices upon annealing. A correlation has been observed between the presence of particular defects and the inhibition of dopant-enhanced superlattice mixing.

We report the first investigation of the effect of dry etching parameters on the sidewall carrier recombination rate of GaAs/AIGaAs and lnPilnGaAsP microstructures. Surface recombination was measured as a function of ion voltage and etching time. The increase in recombination rate due to etching can be reversed by subsequent chemical removal of the immediate sidewall layer. By monitoring the recovery in recombination rate as a function of the amount of sidewall layer removed, the effective damage depth is inferred.

The electron traps of GaAs/AlGaAs heterostructures or superlattices (S.L.) have been investigated in a series of device structures which ranged from simple Schottky diodes to high electron mobility transistors. For the S.L. structure traps investigated, emission into the El miniband as well as A1GaAs trapping was considered. In simple heterostructures such as HEMTs, DLTS investigation of electron trapping from the 2DEG channel revealed a number of new traps, which were previously undetected with CTS (Current Transient Spectroscopy) investigations of the 2DEG. Interface traps in GaAs/AIGaAs heterojunctions were also investigated and distinguished from previously reported traps.

The effect of rapid thermal annealing (RTA) on the shapes of silicon dioxide capped symmetric coupled double GaAs/AlGaAs quantum wells (CDQW) has been investigated. In contrast to previous results on single quantum wells in which increases in exciton energies were observed after RTA, large decreases in exciton energies were seen in CDQWs. Furthermore, there was clear evidence, in the excitation spectrum and in increases in the lowest energy exciton lifetime, of asymmetry present in the heterostructure after RTA.

We combine chemical lattice imaging with digital pattern recognition to study atomic interdiffusion at individual CdTe/HgCdTe interfaces in multi-quantum well structures. In this way we obtain quantitative composition profiles for “as grown” samples, and investigate their development as a function of annealing temperature. Our results indicate that interdiffusion depends on the position of the quantum well with respect to the surface, beginning first at quantum wells close to the surface, and proceeding towards the substrate. Our approach allows the quantification of interdiffusion as a function of time, temperature, and distance from the surface. The implications of these results for the stability of CdTe/HgCdTe structures, and the interpretation of X-ray data are discussed.

MIcrostructural characteristics of phase separated and ordered ternary and quaternary layers of Ill-V compound semiconductors grown by a variety of techniques are highlighted. It is argued that the fine scale contrast modulations seen in a number of layers arise from a two-dimensional, surface spinodal decomposition at the growth temperature. On the other hand, coarse contrast modulations could result from accommodation of asymmetrical strains associated with the twodimensional decomposition.

Long range atomic order is observed in a variety of layers grown by different techniques and co-exists with phase separation. In InGaAs and InGaAsP layers, grown on (001) InP substrates, ordering is observed only on the two {111} planes that contain the line of intersection of the {111}in plane with the (001) InP surface. As a result of ordering, periodicity along the 〈111〉 direction is doubled. Also, the influence of growth temperatures and growth rates on ordering characteristics in GalnP and (Ga, Al) InP layers is reported.

Epitaxial InAs layers were grown by molecular beam epitaxy (MBE) on GaAs substrates. The initial stages of nucleation were studied by in situ reflection high energy electron diffraction (RHEED). Cross-sectional TEM examination was used to investigate the morphology of the growing layer, while plan-view examination revealed the generation of misfit dislocations. The growth mode was found to depend mainly on the conditions used to nucleate the epitaxial layer. In most cases, Stranski-Krastanov type of growth was observed.

Transmission electron microscope (TEM) images of inversion domain boundaries (IDB) show fringe contrast, thus indicating a relative displacement between the two adjoining domains. When the IDBs are facetted, different facets may have different displacement fault vectors. This implies that when the facetting changes from one plane to another, there should be a dislocation at the intersection of the planes. This is termed an “inversion domain boundary dislocation” and it will have a Burgers vector b=R1–R2 where R1, and R2 are the fault vectors of the two facets. Experimental results for facetted IDBs and IDB dislocations in SiC grown heteroepitaxially on (001) silicon are presented.

Epitaxial GaAs layers have been grown by molecular beam epitaxy on (1012) sapphire and silicon-on-sapphire substrates. The grown layers were characterized by optical and transmission electron microscopy; Rutherford backscattering/channeling of 2.1 MeV He+ ions; Raman spectroscopy; Hall mobility measurements; photoluminescence spectroscopy and current-voltage measurements from metal-semiconductor contacts. The extensive microstructural, electrical and optical analysis of the GaAs layers indicates that the films deposited on silicon-on-sapphire are superior to those grown directly on (1012) sapphire substrates.

We report on a systematic study of the composition and structure of GaAs/InAs/GaAs quantum wells using Auger Electron Spectroscopy (AES), Extended Energy Loss Fine Structure (EELFS), and Reflection High Energy Electron Diffraction (RHEED) techniques. Double heterostructures with InAs thickness ranging from 2 to 10 monolayers, capped by 2 to 10 monolayers of GaAs, were grown by MBE using a variety of techniques, including those employing sequential, interrupted, and delayed shutter timing sequences. AES peak ratios are compared with model calculations to monitor compositional development of the multilayers. The AES results are correlated with RHEED measurements to determine MBE growth parameters for optimal control of the stoichiometry and surface morphology. EELFS was used to monitor strain in the buried InAs layers. The AES results show departure from smooth laminar growth of layers of stoichiometric InAs on GaAs at temperatures below 420 C and above 470 C. AES results on the quantum well structures suggest floating InAs layers on top of the GaAs and/or facet formation in the GaAs layers. The EELFS results, when compared to bulk InAs, indicate the presence of strain in the buried InAs quantum well.

We have studied the effects of In doping on the electrical properties of a liquid phase epitaxially (LPE) grown GaAs. The I–V characteristics of Au-GaAs Schottky diodes show, for the layer with In concentration of 2.4 × 1019 cm−3, an ideality factor close to 1.04 over more than seven decades of current. For the same sample, the reverse I–V characteristics are close to an ideal Schottky diode and can be fitted by a theoretical curve, combining the thermionic field emission and thermionic emission. The electrical improvement is closely related to the low etch pit density and other structural improvements. This indicates that, as in the LEC growth, In has effects on the reduction of disloation density in the LPE grown GaAs epi-layer. For doping levels higher than 6×1019 cm−3, an excess forward current is produced at low voltages and low temperatures. A large leakage current is observed under the reverse bias. This property is attributed to a high field effect, with field emission via a trap state as the most likely cause. Hall measurements showed that the ratio of free-carrier concentration ND−NA to the total-carrier concentration ND+NA increased with increasing In concentration.

We have carried out the first systemmatic investigation on the effect of substrate temperature and arsenic partial pressure on the morphology, growth rate, and compensation ratio of Si-doped GaAs, and the Al content of AlxGa1−xAs grown on just-cut (100), (110), (111)A&B, (311)A&B orientated GaAs substrates by gas source MBE (GSMBE). Triethylgallium ( TEG, Ga(C2H5)3 ) and triethylaluminium ( TEA, Al(C2H5)3 ) were used as group III sources, and solid arsenic ( As4 ) and silicon as a group V and IV sources, respectively. The best GaAs mophology was obtained at relatively high temperatures and arsenic pressures. The A orientations were identified as ‘fast surfaces,’ with the GaAs growth rate being comparable to the (100) orientation. The B orientations were identified as ‘slow surfaces,’ with the GaAs growth rate being much less (approximately 50% for the (111)B orientation ) than on the (100) orientation. The least compensated Si-doped GaAs was grown on the (311)A orientated substrate. The Al content, x, (nominally x=0.27 for (100)) of AlxGas1−xAs grown on (110), (111)A&B, was less than 0.05 and not affected by the growth conditions. The Al content of epilayers grown on (311)A&B ranged between x=0.1 to 0.27, strongly depending on the growth temperature.

These results show that using GSMBE we can selectively modifying a large range of (Ga,Al)As crystal properties. Potential applications include the selective growth and realisation of ultra-fine and planar structures and devices.

An understanding of the mechanisms of self-diffusion and of interdiffusion in the compound materials GaAs and AlAs may be arrived at byt noting the effects of (i) charge, (ii) As pressure, and (iii) point defect supersaturation, on the doping enhanced superlattice disordering phenomena. The Ga self-diffusion (and hence Ga-Al interdiffusion) is dominated by the triply-negatively-charged Ga (or Al) vacancy, , under intrinsic and n-doping conditions. Under p-doping, a positively charged Ga self-interstitial , with m not known, contributes to the Ga(AI) diffusion process. Less is known for the group V element diffusion, but the As vacancy (VAs) should be contributing under intrinsic and n-doping conditions while the As selfinterstitial (LAs) may be contributing under p-doping. The contribution of a defect pair may also be involved under p-doping.

Sealed ampoule Zn diffusions into an unstrained In0.53Ga0.47As/InP superlattice are observed to preferentially induce cation (In, Ga) interdiffusion. The extent of interdiffusion is monitored in these studies by SIMS (secondary ion mass spectrometry). In some cases, Zn entirely displaces In in the InP layers forming an In1−xGaxAs/Zn3P2 superlattice. Under still more stringent conditions, all In and Ga is replaced, resulting in a Zn3As2/Zn3P2 superlattice. These structures are capable of supporting considerable strain due to the absence of grown-in defects. TEM (transmission electron microscopy) micrographs of several samples reveal defect free highly strained layers with thicknesses exceeding the predicted critical values. A high dose Zn implant was examined in which mixing proceeded until the Zn concentration dropped below a threshold concentration of approximately 1020 cm−3 during the anneal. These results, in total, strongly support a kickout mechanism for Zn induced mixing. Si diffusion was observed, in one case, to induce comparable cation and anion interdiffusion, thereby reducing the layer bandgap disparity, as opposed to Zn which increases the difference in layer bandgaps. Almost no interdiffusion was induced by Si diffusion from MBE (molecular beam epitaxy) polycrystalline Si films, due either to the very high resultant Si concentrations or to the capping effect of the film. The data suggest that both anion and cation site defects play a role in the Si induced mixing process.

We studied doping Se into AlGaAs layers using PbSe as a dopant source for molecular beam epitaxy (MBE). Good controllability and abruptness equivalent to that of Si-doping were obtained. Se-doping was successfully applied to HEMT structures with reduced DX center concentrations. The two dimensional electron gas (2DEG) characteristics of these structures were comparable to those of Si-doped structures.

We describe here an effort to provide lateral confinement of carriers within a continuous InGaAs quantum well by creating a pattern of strain in the well. A compressed InGaAsP layer overlying the quantum well and the InP barrier was patterned into submicron stressor wires by etching to within approximately 20 nm of the InP barrier. The relaxation of the compression at the edges of the quaternary stressors resulted in dilation of the quantum well material under their centers, thus lowering the band gap of the material, providing confinement for both electrons and holes there. We observed a red shift of the quantum well luminescence of 7 meV for 400 nm wide wires, evidence for the strain-induced lateral confinement. This is the first observation of a red-shifted band gap in submicron strain-confining structures.

Recent progress of GaAs-on-Si technology is reviewed and the importance of initial nucleation is emphasized. Growth initiation with a Ga prelayer at a suitable low temperature combined with migration enhanced epitaxy and in-situ thermal annealing has a prospect of giving substantially improved material quality. During the initial growth, use of the minimum necessary As4/Ga flux ratio is found to be critical. The random alignment of the major axis of the oval defects is suggested to be an alternative simple technique to detect the presence of antiphase domains. Patterned growth or post growth patterning releases tensile stress only if the growth edges are free. GaAs-on-Si was completely relaxed from stress by post-growth patterning to 5 μm × 5 μm size patterns. Steps on the surface due to substrate misorientation do not affect the two dimensional electron gas (2DEG) transport properties in AlGaAs/GaAs selectively doped heterojunction transistor (SDHT) structures. For a sheet density of 1012 cm−2, the 2DEG mobility >50,000 cm2V−1s−1 at 77 K was obtained on Si substrates, which is sufficient for fabrication of high performance SDHTs. The study shows that GaAs-on-Si has a great potential for SDHT technology.

Low temperature photoluminescence results from MOCVD epitaxial InP grown on GaAs/Si substrates are presented as a function of thickness of the GaAs buffer layer. As a consequence of thermal expansion mismatch of the heterostructure, the InP layer contains residual stress which causes the band gap to shift and splits the valence band degeneracy of the mj = ± 3/2 and the mj = ± 1/2 bands. Both the shifting and splitting phenomena are clearly seen in tite PL results and are shown to depend on the GaAs buffer layer thickness.

Improvements of crystal quality in GaAs/Si heterostructure by solid phase epitaxy (SPE) are described. RBS and TEM measurements indicate that high density defects are located near the GaAs/Si interface after “2-step MBE”. Utilization of post SPE process (amorphization plus regrowth) significantly improve crystal qujali ty at the GaAs/Si interface, although a small stress field is introduced. In addition a new relation between photoluminecence intensity ratio and stress field is established. This provides a useful too] for measuring small stresses remaining in the GaAs/Si hetero-structure.

We first report on migration-enhanced molecular beam epitaxial (MEMBE) growth and characterization of the GaAs layers on Si substrates (GaAs/Si). Excellent surface morphology GaAs layers were successfully grown on (100) Sisubstrates misoriented 4 toward [110] direction. The MEMBE growth method isdescribed and material properties are compared with those of normal two-step MBE-grown or in-situ annealed layers. Micrographs of cross-sectional view transmission electron microscopy (TEM) and scanning surface electron microscopy (SEM) of MEMBE-grown GaAs/Si showed dislocation densities of 107 cm-2 over ten times lower than those of two-step MBE-grown or in-situ annealedlayers. AlGaAs/GaAs double heterostructure lasers and light-emitting diodeshave been successfully grown on MEMBE GaAs/Si by both metal organic chemical vapor deposition and liquid phase epitaxy. MOCVD-grown lasers showed peak output power as high as 184 mW/facet, pulsed threshold currents as low as150 mA at 300 K, and differential quantum efficiencies of up to 30 %. The LPE-grown light-emitting diodes showed output powers of 1.5 mW and external quantum efficiencies of 3.3 mW/A per facet.