Ti0.5Al0.5N alloy films, typically 1.5 μm thick, were grown on MgO(001) at temperatures Ts between 400 and 850 °C by ultra‐high‐vacuum reactive magnetron sputtering in pure N2. Films grown at Ts between ≂480 and 560 °C were single crystals in which the lattice misfit strain was partially relieved by glide of 〈001〉 misfit dislocations, with Burgers vector =a0/2〈011〉, on {011} planes. Cross‐sectional transmission electron microscopy investigation showed no evidence of residual extended defects in the films until thicknesses of ≂150 nm at which point threading dislocations, oriented along the [001] growth direction, were observed. Surface‐initiated spinodal decomposition, resulting in the formation of compositionally modulated NaCl‐structure platelets along [001] with width ≂1 nm, occurred over a narrow growth temperature range between 540 and 560 °C as a precursor to bulk phase separation of wurtzite‐structure AlN at Ts≥560 °C. The alloy was continuously depleted of AlN at higher growth temperatures until ...

Defect structure and phase transitions in epitaxial metastable cubic Ti0.5Al0.5N alloys grown on MgO(001) by ultra‐high‐vacuum magnetron sputter deposition

Using compositionally graded buffers, we demonstrate InP on GaAs suitable for minority carrier devices, exhibiting a threading dislocation density of 1.2×106∕cm2 determined by plan-view transmission electron microscopy. To further quantify the quality of this InP on GaAs, a photoluminescence (PL) structure was grown to compare the InP on graded buffer quality to bulk InP. Comparable room and low temperature (20K) PL was attained. (The intensity from the PL structure grown on the InP on GaAs was ∼70% of that on bulk InP at both temperatures.) To achieve this, graded buffers in the InGaAs, InGaP, InAlAs, and InGaAlAs materials systems were explored. In each of these systems, under certain growth conditions, microscopic compositional inhomogeneities blocked dislocation glide and led to threading dislocation densities sometimes >109∕cm2. These composition variations are caused by surface-driven, phase separated, Ga-rich regions. As the phase separation blocked dislocation glide and led to high threading dislo...

Relaxed, high-quality InP on GaAs by using InGaAs and InGaP graded buffers to avoid phase separation

The elastic energy associated with alloy composition modulation in the epitaxial film of a III‐V semiconductor alloy on the [001]‐substrate is calculated in the analytic form. Composition modulation both in the directions parallel to the substrate surface and in the growth direction are taken into account. It is shown that the minimum of the elastic energy corresponds to the modulation along the [100]‐ (and/or [010]‐) direction, the period of the modulation d being small compared to the film thickness h (d≪h). The ‘‘soft mode’’ of composition modulation is exponentially localized near the free surface, the localization length l being l=d/2π. The elastic energy caused by this modulation is less by the factor 1/2c11/(c11+c12) than the elastic energy corresponding to spinodal decomposition in the bulk sample. This factor is ≊1/3 for III‐V alloys. Critical temperatures of spinodal decomposition Tc are calculated for a number of epitaxial ternary III‐V alloys. The diffusion which occurs only in the very thin s...

On spinodal decomposition in elastically anisotropic epitaxial films of III‐V semiconductor alloys

Rapid decrease of differential gain has been determined to dominate the temperature dependence of threshold current in 1.3-/spl mu/m multiquantum well and bulk active lasers giving rise to low values of T/sub 0/. Extensive experimental characterization of each type of device is described. Results are presented for the dependence of gain on chemical potential and carrier density as a function of temperature. The data indicate the important role of the temperature-insensitive, carrier density dependent chemical potential in determining differential gain. Modeling of the temperature dependence of threshold carrier density in MQW and bulk active lasers based on a detailed band theory calculation is described. The calculated value of T/sub 0/ depends on the structure of the active layer, e.g., multiquantum well versus bulk. However, the calculated values are substantially higher than measured. >

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Analysis of gain in determining T/sub 0/ in 1.3 /spl mu/m semiconductor lasers

InxGa1−xAs structures with compositionally graded buffers were grown with organometallic vapor phase epitaxy on GaAs substrates and characterized with plan-view and cross-sectional transmission electron microscopy, atomic force microscopy, and x-ray diffraction. The results show that surface roughness experiences a maximum at growth temperatures where phase separation occurs in InxGa1−xAs. The strain fields from misfit dislocations induce this phase separation in the 〈110〉 directions. At growth temperatures above and below this temperature, the surface roughness is decreased significantly; however, only growth temperatures above this regime ensure nearly complete relaxed graded buffers with the most uniform composition caps. With the optimum growth temperature for grading InxGa1−xAs determined to be 700 °C, it was possible to produce In0.33Ga0.67As diode structures on GaAs with threading dislocation densities <8.5×106/cm2.

Relaxed InxGa1−xAs graded buffers grown with organometallic vapor phase epitaxy on GaAs

Composition modulation due to spinodal decomposition in In1−xGaxAsyP1−y quaternary and In1−xGaxAs ternary alloys is observed by transmission electron microscopy in epitaxial layers grown by hydride transport vapor phase epitaxy at 700 °C on (001) InP substrate A quasi‐periodic fine contrast oriented along [100] and [010] directions is found in all samples over a composition range of 020≤x≤053 and 037≤y≤1 Contrary to the result reported on materials grown by liquid‐phase epitaxy, complete mixing at composition outside the miscibility gap predicted by thermodynamics for bulk crystals is not observed The evidence indicates a rapid spinodal decomposition by surface diffusion during vapor phase deposition Furthermore, transmission electron microscopy diffraction contrast experiments on the (110) cross‐sectional view of planar and nonplanar epitaxial layers reveal a columnar structure oriented along the growth direction which is consistent with the surface layer spinodal formation Additional coarse cont

K. E. Strege

Papers

Surface layer spinodal decomposition in In1−xGaxAsyP1−y and In1−xGaxAs grown by hydride transport vapor‐phase epitaxy