GaAs is grown embedded in pre-etched wells in the Si substrate. HNO3:HF, KOH:H2O and a dry etch technique are used as alternatives to form the wells. Cross-sectional SEM views of AlGaAs/GaAs heterostructures reveal the growth front and facet formation for the different sidewall geometries. Transmission electron microscopy is used to study epilayer degradation in relation to the substrate damage and the presence of edge induced defects in the GaAs. Cathodoluminescence reveals the uniformity of strain present in the GaAs layer embedded in the wet etched well. The impact of the different etching techniques on device integration is briefly discussed.

The biaxial tensile stress of 2.65 kbar in as-grown GaAs/Si for T < 100K is reduced by post-growth patterning of the GaAs and the reduction in stress, as determined by photoluminescence and cathodoluminescence, is dependent on the pattern size and shape. For stripe patterns less than 15 gm wide the stress is largely uniaxial with stress relief normal to the stripe direction. Rectangular patterns exhibited stress relief in orthogonal directions, and a 9 x 12 µm2 rectangle exhibited an average stress of 0.5 kbar. For as-grown GaAs/Si layers 0.9 to 3.25 µm thick, the stress is weakly dependent on layer thickness. For T > looK the stress in as-grown GaAs/Si is reduced and at 295K a value of 1.51 ± 0.21 kbar is obtained. With patterned growth, using a native SiO2 mask, no reduction in stress was observed irrespective of the pattern size, indicating the importance of free GaAs edges in obtaining stress relief.

The characteristics of GaAs layers grown by MBE at growth temperatures from 200 °C to 400 °C have been evaluated by photoconductivity experiments in order to understand the photoelectronic properties of this material. Low temperature (LT) growth of GaAs on both silicon and GaAs substrates has been investigated in an attempt to better understand the nature of defects which are created in epitaxial layers grown under these conditions. Results from experiments on both annealed and unannealed LT samples indicate that the electronic transport properties of the epilayers can be controlled by selecting the appropriate growth conditions.

Epitaxial GaAs films have been deposited on Si substrates using Atomic Layer Epitaxy (ALE) for the first time. This has been achieved in a SPI-MO CVD™ 450 reactor especially modified foroALE. After an initial high temperature bakeout, a nucleation layer 100-300 Å thick was deposited by ALE. Film growth was then resumed by conventional MOCVD to achieve the desired film thickness. The surface morphologies of the deposited films were found to be comparable to current state of the art conventional GaAs on Si films deposited by the two-step growth process in the same reactor.

Selective area epitaxy of GaAs on Si has also been achieved on Si02-coated and patterned Si wafers. The standard two-step deposition technique resulted in epitaxial growth in the patterned windows and poly-GaAs on the oxide mask, while ALE growth resulted in deposition only in the etched windows with no poly-growth on the oxide mask. We will report on the potential of this new deposition technique in producing high quality GaAs-on-Si films.

A comparison is made between the interface formed when GaAs is grown heteroepitaxially on Si(100) substrates with that formed for ZnSe-on-Si(100) growth. Results of core level photoemission spectroscopy show that the Si(100) surface reacts with As atoms to form a stable monolayer, but reacts with Se atoms to form the compound SiSe2. Annealing treatments can also give rise to a submonolayer coverage of Se atoms on Si(100). The SiSe2 compound is also seen at the interface between ZnSe and Si. Island formation appears to occur at the beginning of growth for both GaAs-on-Si and ZnSe-on-Si

GaAs layers have been successfully grown on tilted (100) Si as well as porous Si substrates by molecular beam epitaxy(MBE). Rapid thermal annealing and vacuum thermal annealing have been used to further improve the quality of the epitaxial layers. We observed that the dislocation density near the interface of the heterostructure is higher for GaAs on Si substrate. Both annealing processes are proven to be useful in improving layer quality, while the vacuum thermal annealing seemed to be more effective in minimizing the residual stress.

GaAs-on-Si structures have been grown by atmospheric-pressure metalorganic chemical vapor deposition (MOCVD); in some samples, the GaAs nucleation layer was deposited by atomic layer epitaxy (ALE). Material quality has been characterized by Nomarski microscopy, time-resolved photoluminescence, trans- mission electron microscopy, and the performance of photovoltaic devices. The minority-carrier lifetime has been correlated with defect density and growth parameters. The use of a thermal-cycle-growth technique is seen to be a major factor in improving GaAs-on-Si material quality without resorting to the use of thick buffer layers.

Nominal 100 Å and 150 Å thick GaAs layers were deposited on Si substrates by a modulated molecular beam technique and normal molecular beam epitaxy (MBE) at 300 °C and 375 °C respectively for plan view and cross-sectional transmission electron microscopy (TEM) examinations. From coverage of Moire fringes, it is found that the nucleated GaAs films grown by the modulated molecular beam technique were thinner, streaker and more two-dimensional than the MBE grown films. The same modulated molecular beam technique was also used for the deposition of the initial buffer layer of 3µm thick GaAs on Si films. Results from the 77k photoluminescence(PL) and double crystal X ray diffraction measurements showed that these films have superior optical and structural quality compared to similar films grown by normal two-step MBE. The improvement is attributed to a more two-dimensional nucleation of GaAs films associated with the modulated molecular beam growth technique.

Gallium arsenide epitaxial layers with excellent morphology have been grown by organometallic chemical vapor deposition (OMCVD) on (100) and 2-3° off (100) InP substrates by a modified two-step growth commonly used for GaAs on Si. The layers have been characterized by X-ray diffraction, cross-sectional transmission electron microscopy (TEM), low temperature photoluminescence (PL) and Hall measurements. 1 µm gate GaAs metal-semiconductor field effect transistors (MESFETs) with transconductances as high as 220 mS/mm have been fabricated. These MESFETs have been integrated with buried heterostructure and V-groove InGaAsP lasers. The V-groove laser -MESFET OEIC transmitter has been shown to be capable of direct modulation at 5 Gb/sec bit rate. Finally we have also demonstrated GaAs single quantum well lasers with threshold currents as low as 800 A/cm2for 50 µm wide broad area gain guided devices with 1.25 mm long cavities.

Extensive new data and modeling in the In-Ga-As system has allowed the authors to reexamine the phase equilibria between the melt and the epitaxial solid. A detailed thermodynamic model was constructed with the following improvements: (1) The solid-solid interaction parameters were based on InAs-GaAs miscibility gap data, and (2) liquid-bulk solid, as well as liquid-epitaxial solid, tie-lines were used. Comparison of tie- lines from epitaxial systems and bulk systems demonstrated that strain energy is not the dominant factor in equilibrium growth of epitaxial solid films of In1-xGaxAs on any Ill-V binary substrate. Both the “lattice- pulling” effect and the “substrate-orientation” effect were shown to be caused by different quaternary equilibria at the In1-xGaxAs/InP interface, and not by film-substrate strain.

The density and arrangement of dislocations in In0.15Ga0.85As grown on GaAs(100)) were determined by transmission electron microscopy as a function of misorientation toward (111)A, (111)B, and (110). Strained layer superlattices were used in all cases to reduce dislocation density. Layers grown on exact GaAs(100) exhibited a non-uniform threading dislocation dis- tribution whereby some areas had a high density (∼ 109cm-2or higher) of dislocation tangles and other areas that we in between had a more uniform density (∼ 2 x 107cm-2). The misorientated layers exhibited a uniform threading dislocation distribution with densities of ∼ 5 x 106 cm-2 for (100) misoriented towards (111)A, ∼ 1 x 107cm-2towards (111)B, and ∼ 3 x 107cm-2 towards (110). The misfit dislocation network (dislocations located at the GaAs-InO0.15Ga0.85 As interface) formed orthogonal dislocation arrays in the case of exact (100) substrates and slightly non-ortho- gonal arrays in the case of misoriented substrates. These results are explained with the help of a general glide model of strain relaxation in which the exact (100) orientation has eight equally stressed glide systems which presumably activate during strain relaxation. With misoriented substrates the stress symmetry is broken and fewer glide systems experience the maximum stress, thus reducing the number of active dislocation systems. A small asymmetry in interfacial dis- location density was observed in all the cases where the linear dislocation density along the two (011) and (011) orthogonal directions differed by about 20%. This is explained by the preferred activation of (x-dislocations (high dislocation mobility) over 13-dislocations (low dislocation mobility).

In heavily dislocated GaAs (dislocation density of 108cm-2), the low-temperature cathodo- luminescence efficiency of quantum wells and superlattices is dramatically higher than that of a bulk-like layer. Furthermore, the luminescence efficiency can be further improved by doping the barriers of the GaAs/(Al,Ga)As multi-quantum well structures with beryllium (Be). Two quite different possible models for this observation are discussed: One assumes that the effect is due to the expulsion of dislocation kinks from the wells, the other that it is due to the effect of well width fluctuations.

We have employed molecular beam epitaxy in the growth of InSb on GaAs and InP. The transport, optical and structural properties of the films were investigated by in-situ reflection high energy electron diffraction, Hall effect and temperature dependent Hall effect, photoluminescence, transmission electron microscopy and X-ray diffractometry techniques. We report mobilities of up to 32,000 cm2/volt-sec and free electron concentrations of 3x1016/cm3 at room temperature. We have discovered a new defect state in InSb with an energy position of Ec - 0.05 ± 0.006eV. Optical and structural measurements reveal that the differences in thermal expansion and lattice mismatch between the substrates and films results in the broadening of the X-ray diffraction peaks and the near gap photoluminescence linewidths. Furthermore, we observe band gap shifts to higher energies of 10meV and 20meV for growth on GaAs and InP, respectively.

We present a detailed photoluminescence and photoluminescence excitation study of GaAs grown directly on InP substrates by MOCVD. Reliable peak assignments are determined. With these peak assignments, we measure strain and strain uniformity, identify impurities, and assess material quality. Most samples exhibit three distinct spectral features. The two highest energy features are the strain split valence band, the third feature is a carbon impurity. The observed splitting is in good agreement with the value predicted from the thermal expansion mismatch.

We have grown a number of InAs and GaSb bulk layers on GaAs substrates and studied the properties of the semiconductor films as a function of the various growth parameters. Preliminary results from GaSb growth are presented in addition to an extensive study of InAs growth. The films were characterized during growth by RHEED. RHEED-oscillations were observed during both InAs and GaSb growths. Hall effect measurements yielded peak electron mobilities for InAs of 18,900 cm2/Vs at 300 K and 35,000 cm2/Vs at 77 K. For GaSb the as grown layers were found to be p-type with a carrier concentration of 9x1015cm-3 and a hole mobility of 910 cm2 /Vs at 300 K.

We present data on electron transport in AlSb/InAs/AlSb quantum wells grown by molecular beam epitaxy. Because both anion and cation change across an InAs/Alsb interface, it is possible to grow such wells with two different types of interfaces, one with an InSb-like bond configuration, the other AlAs-like. Electron mobility and concentration were found to depend very strongly on the manner in which the quantum well's interfaces were grown, with high mobilities seen only if the bottom interface is InSb-like. An As-on-Al sites antisite defect model is postulated for bottom AlAs-like interfaces.

The electrical properties of pseudomorphic ZnSe/epilayer GaAs heterointerfaces, grown by MBE, have been investigated by capacitance versus voltage (C-V) and current versus voltage (I- V) measurements. Hole accumulation and inversion were observed in ZnSe/p-GaAs interfaces and ZnSe/n-GaAs interfaces, respectively. The C-V characteristics of the Au/ZnSe/p-GaAs capacitors are nearly ideal, exhibiting an interface state density (2.5x1011cm-2) which compares favorably with the densities reported at AlGaAs/GaAs interfaces.

Low-temperature photoluminescence and plane-view TEN observations have been carried out to investigate the strain and microstructural defects in MOCVD-grown ZnSe/(100)GaAs after post- growth annealing in H2gas at temperature between 350 and 500V. A 0.35 µm thick ZnSe epitaxial layer is originally under compres- sive strain, but after annealing this receives considerably tensile strain, and the neutral deep-acceptor bound exciton () line and the edge-emission band at about 2.72 eV newly appear. The observed changes are interpreted in terms of the energy down- shift of the excitonic lines and deviation from stoichiometry. The annealed film, which deteriorated as a result of generations of dislocation tangles and small loops, results in the strong deep-level emissions around 2.25 eV.

Reflection high energy electron diffraction (RHEED) intensity oscillations are often used to investigate in situ the growth of III-V materials by molecular beam epitaxy (MBE). In this work, we have used RHEED oscillations to perform a quantitative study of the growth mechanisms of ZnSe, a II-VI semiconductor.

Our experiments illustrate that the RHEED pattern of ZnSe is far less intense than that of III-V materials grown by MBE, and no specular spot is observed over a wide range of growth conditions. We have, however, been able to record up to 25 oscillations allowing a quantitative study of the growth of ZnSe by MBE. Thus we have used RHEED oscillations to make an in situ systematic study of the influence of the three main growth parameters (substrate temperature and Zn or Se impinging fluxes) on the ZnSe growth rate. We observed that the variation of the ZnSe growth rate is due to a non unity sticking coefficient of both Zn and Se species at the interface in the standard growth conditions used. Our observations can be described using a thermodynamic model and enable us to control the desired growth conditions. Our work demonstrates the utility of RHEED oscillations to understand the MBE growth mechanisms of II-VI compounds.

The electronic transport properties of ZnSe layers grown by MBE on GaAs sub- strates are studied by small-signal ac admittance, dc current-voltage, and Hall effect measurements. This work is supplemented by a study of TEM and x-ray rocking curve data. We find that the transport characteristics are strongly affected by the proper- ties of the ZnSe/GaAs interface. From the dc and ac measurements, we determine the total barrier height at the interface of thick (1-6 µm) ZnSe layers on n+-GaAs, and find that it is in general voltage dependent. While some samples are found to have a very high peak mobility (> 10,000cm2 /Vsec), an anomalous reduction in the mobility in a large fraction of the samples is found, and attributed to the presence of non- uniform space charge regions.