R. M. Cohen

Effect of mismatch strain on band gap in III‐V semiconductors

Interfacial elastic strain induced by the lattice parameter mismatch between epilayer and substrate results in significant energy–band‐gap shifts for III‐V alloys. The epilayers used in this study are GaxIn1−xAs on (100) InP and GaxIn1−xP on (100) GaAs prepared by organometallic vapor phase epitaxy. For layer thicknesses between 1 and 1.5 μm, and Δas.f./a0≤3.5×10−3 the misfit strain is assumed to be accommodated elastically. The energy–band‐gap shifts are determined by comparing the photoluminescence peak energies of the epilayers with the best experimental relation of band gap versus composition for unstrained layers. A calculation of the energy–band‐gap shift due to biaxial stress made for GaxIn1−xAs is found to agree with the photoluminescence measurements. In addition, a comparison of the energy–band‐gap shift for GaxIn1−xP shows a clearly different dependency for tensile and compressive strain, in good agreement with calculated results.

Photoluminescence of InSb, InAs, and InAsSb grown by organometallic vapor phase epitaxy

Infrared photoluminescence (PL) from InSb, InAs, and InAs1−xSbx (x<0.3) epitaxial layers grown by atmospheric pressure organometallic vapor phase epitaxy has been investigated for the first time over an extended temperature range. The values of full width at half maximum of the PL peaks show that the epitaxial layer quality is comparable to that grown by molecular‐beam epitaxy. The observed small peak shift with temperature for most InAs1−xSbx epilayers may be explained by wave‐vector‐nonconserving transitions involved in the PL emission. For comparison, PL spectra from InSb/InSb and InAs/InAs show that the wave‐vector‐conserving mechanism is responsible for the PL emission. The temperature dependence of the energy band gaps, Eg, in InSb and InAs is shown to follow Varshni’s equation Eg(T)=Eg0−αT2/ (T+β). The empirical constants are calculated to be Eg0=235 meV, α=0.270 meV/K, and β=106 K for InSb and Eg0=415 meV, α=0.276 meV/K, and β=83 K for InAs.

GaAs1−xSbx growth by OMVPE

The system GaAs1−xSbx has a solid phase miscibility gap ranging from x = 0.2 to x = 0.8 at the typical growth temperature of 600 C; however, metastable alloys covering this entire composition range have been grown by organometallic vapor phase epitaxy (OMVPE) using trimethylgallium, antimony and -arsenic as the source materials. The solid composition is studied for various values of growth temperature, the ratio of Sb to total group V elements in the vapor phase and the ratio of group III to group V elements in the vapor phase. The fraction of trimethylarsenic (TMAs) pyrolyzed in the vapor phase is found to be < 1 and to vary with temperature. Taking into account the incomplete pyrolysis of TMAs, solid composition is found to be controlled by thermodynamics. The effects of temperature and vapor composition are all accurately predicted using a simple thermodynamic model assuming equilibrium to be established at the solid-vapor interface. The properties of these metastable GaAs1−x Sbx alloys were explored using interference contrast microscopy, room temperature and 4 K photoluminescence, Hall effect and conductivity measurements. The alloy GaAs0.5Sb0.5 grown lattice matched to the InP substrate has excellent surface morphology, is p-type, and the photoluminescence spectrum consists of a single, intense, fairly broad (23.5 meV half width) peak at a wavelength of 1.54 Μm.

Organometallic vapor phase epitaxial growth of high purity GaInAs using trimethylindium

Gax In1−xAs lattice matched to the InP substrate (x=0.47) has been grown by organometallic vapor phase epitaxy using trimethylindium (TMIn) and trimethylgallium (TMGa) as the group III sources and AsH3 as the As source. In a simple, horizontal, atmospheric pressure reactor, the GaInAs growth proceeds without visible evidence of parasitic prereaction problems. The process yields homogeneous, reproducible GaInAs with a high growth efficiency and a solid/vapor In distribution coefficient of nearly unity. Most importantly, several layers with room‐temperature electron mobilities of approximately 10 000 cm2/Vs and carrier concentrations of approximately 1015 cm−3 have been produced. The 4‐K photoluminescence shows a narrow (4–5 meV) band‐edge emission peak and a low‐intensity band acceptor peak at ∼18 meV lower energy. Surface morphologies are routinely featureless as observed by high magnification interference contrast microscopy.

OMVPE growth of InP using TMIn

Abstract The organometallic vapor phase epitaxial (OMVPE) growth of InP is described for a simple, atmospheric-pressure system using trimethylindium (TMIn) as the In source. The growth process exhibits no signs of polymer predeposition problems which have plagued several previous efforts to grow In containing compounds and alloys. The effects of growth temperature, in the range 525 to 700°C, on growth rate, morphology, photoluminescence intensity and spectral half-width, and electron mobility are reported.

Organometallic vapor phase epitaxial growth of GaAs0.5Sb0.5

The pseudobinary III/V system GaAs1−ySby is well known to have a solid phase miscibility gap with a critical temperature of 751 °C. We have succeeded in growing epitaxial layers of GaAs0.5Sb0.5 lattice matched to InP at temperatures of 600 and 630 °C using the organometallic vapor phase epitaxy technique. The key requirement is a III/V ratio of greater than unity. This leads to the incorporation of all As and Sb reaching the interface and the ability to grow metastable alloys. The epitaxial GaAs0.5Sb0.5 layers have excellent surface morphology and efficient photoluminescence at a wavelength of 1.6  μm.

InAsBi alloys grown by organometallic vapor phase epitaxy

InAsBi is a III/V alloy with potential application for detectors in the 8–12 μm region of the spectrum. Growth of InAs1-xBix, with x ≤ 0.054, at 350°C by atmospheric pressure organometallic vapor phase epitaxy has been made possible by using a new combination of precursors, ethyldimethylindium (EDMIn), tertiarybutylarsine (TBAs) and trimethylbismuth (TMBi). Results were obtained using a V/III ratio between 21 and 22. With these conditions, a Bi distribution coefficient of 1.746 was measured. X-ray diffraction verifies that Bi incorporates substitutionally into the zincblende structure. For x < 0.045, it was possible to suppress whisker formation and obtain excellent surface morphology. Measurement of photoluminescence for x ≤ 0.037 indicates good crystal quality. The measured rate of change of bandgap with Bi concentration, dEg/dx = -55 meV/%Bi, indicates that a 77 K bandgap energy of E = 0.10 eV should be reached with an alloy composition of InAs0.94Bi0.06.

Organometallic vapor-phase epitaxy growth and characterization of Bi-containing III/V alloys

For potential infrared detector applications, single‐crystalline InAsBi and InAsSbBi have been grown by atmospheric pressure organometallic vapor‐phase epitaxy. The precursors used were trimethylindium, trimethylantimony, trimethylbismuth, and arsine at growth temperatures of 375 and 400 °C. Good quality epilayers with smooth surface morphologies were obtained by properly controlling the key growth parameter, the V/III ratio. The variation of lattice constant with solid composition for the InAs1−xBix system, a=6.058+0.966x, provides evidence that Bi atoms indeed incorporate substitutionally into the As sites of the sublattice in the InAs zinc‐blende structure. An extrapolated lattice parameter for the hypothetical zinc‐blende InBi is 7.024 A. Thermodynamic calculations of the InAs‐InBi and InSb‐InBi pseudobinary phase diagrams were carried out using the delta‐lattice‐parameter model using the lattice constant for zinc‐blende InBi of 7.024 A. The results agree well with experimental data. The calculations ...

OMVPE growth of the metastable III/V alloy GaAs 0.5 Sb 0.5

The two crystal growth parameters most likely to affect the occurrence of GaAs0.5Sb0.5 spinodal decomposition during organometallic vapor phase epitaxial (OMVPE) growth, substrate temperature and substrate orientation, were investigated in detail. The temperature range studied was the widest over which good morphology layers could be grown, from 550 to 680° C. The InP substrate orientations used were (100), (221) and (311). The growth process was found to be diffusion controlled at high temperatures, but to be controlled by surface kinetics at temperatures below approximately 620° C, depending on substrate orientation. Growth of high quality layers was found to be much easier between 570 and 640° C. In addition, the 77 K PL intensity is much stronger for layers grown in this temperature range. The minimum PL halfwidth at 77 K is 20 meV and at 8 K is 16 meV. The typical room temperature hole mobilities are 100 cm2/Vs with hole concentrations of 2 x 1017 cm-3 in undoped material. The temperature dependence of mobility is consistent with enhanced alloy scattering. Surprisingly, the growth temperature has no significant effect on either PL halfwidth or hole mobility between 560 and 660° C. The single Raman line observed for the unannealed alloy is split after annealing into two lines corresponding to the GaAs-rich and GaSb-rich alloys on either side of the range of solid immiscibility. The spinodal decomposition apparently starts at the surface where the coherency strain, which stabilizes the single phase alloy, is smallest.

Organometallic vapor phase epitaxial growth and characterization of InAsBi and InAsSbBi

InAs1−xBix with x≤0.026 and InAs1−x−ySbyBix with x≤0.017 and y≤0.096 have been successfully grown on InAs (100) oriented substrates by atmospheric pressure organometallic vapor phase epitaxy using the precursors trimethylindium, trimethylbismuth, trimethylantimony, and arsine. Good surface morphologies for both InAsBi and InAsSbBi epitaxial layers were obtained at a growth temperature of 400 °C. A key growth parameter is the V/III ratio. Only a very narrow range near 4 (considering the incomplete pyrolysis of AsH3) yields smooth InAsBi epilayers. Typical growth rates were 0.02 μm/min. X‐ray diffractometer scans show clearly resolved Kα1 and Kα2 peaks for the layer of InAs0.889Sb0.096Bi0.015 grown on an InAs substrate with a graded transition layer to accommodate the lattice parameter difference. The half widths of the peaks are comparable to those of the substrate. For the first time, photoluminescence (PL) at 10 K from these Bi‐containing alloys has been measured. The PL peak energy is seen to decrease w...