L. K. Howard

Thermal quenching of the photoluminescence of InGaAs/GaAs and InGaAs/AlGaAs strained‐layer quantum wells

Photoluminescence in InGaAs/GaAs strained‐layer quantum wells is strongly quenched by temperatures above 10–100 K, depending on the well width. Analysis of this dependence shows that the quenching mechanism is thermal activation of electron‐hole pairs from the wells into the GaAs barriers, followed by nonradiative recombination through a loss mechanism in bulk GaAs. The addition of Al to the barriers to improve confinement eliminates loss through this route but introduces another loss mechanism, characterized by an activation energy independent of well width and with a smaller pre‐exponential factor.

Plastic relaxation of InGaAs grown on GaAs

We report measurements of the plastic relaxation of InGaAs layers grown above critical thickness on GaAs substrates. The relaxation is accurately hyperbolic, proportional to the reciprocal of the layer thickness, in agreement with a recent geometrical theory of critical thickness [D. J. Dunstan, S. Young, and R. H. Dixon, J. Appl. Phys. 70, 3038 (1991)]. At large thicknesses, work hardening is observed which leads to a residual strain dependent on the original misfit.

Interdiffusion in InGaAs/GaAs quantum well structures as a function of depth

Interdiffusion in InGaAs/GaAs quantum wells has been studied using photoluminescence to follow the development of the diffusion with time in a single sample. Two distinct regimes are seen; a fast initial diffusion and a second steady‐state diffusion. The steady‐state diffusion was found to be dependent on the depth of the quantum well from the surface and to correlate with published data on the indiffusion of gallium vacancies into gallium arsenide.

Dielectric functions and critical points of strained InxGa1−xAs on GaAs

Dielectric function spectra of strained InxGa1−xAs (x≤0.25) epilayers on GaAs are presented for the first time, together with spectra of relaxed layers of the same compositions. Critical point energies, obtained by line‐shape fitting to second‐derivative spectroscopic ellipsometry (SE) data, show an increase in the E1, E1+Δ1 splitting with strain, in agreement with theory using GaAs deformation potentials. SE is shown to be capable of determining layer thickness, composition, and strain in this alloy system.

The effect of growth temperature on plastic relaxation of In0.2Ga0.8As surface layers on GaAs

Abstract Single surface layers of In 0.2 Ga 0.8 As ranging from 10 nm to 3 μm in thickness have been grown by molecular beam epitaxy (MBE) on GaAs at two growth temperatures, 400°C and 519°C. The residual strain of each layer has been obtained from double crystal X-ray diffraction (DCXD) measurements, and the surface morphology observed by differential interference contrast microscopy. The critical thickness is found to be independent of growth temperature. The effects of the change in growth temperature on the surface morphology and the extent of relaxation with varying layer thickness are discussed.

A photoluminescence study of indium desorption from strained Ga1−xInxAs/GaAs

Abstract In this paper we present detailed measurements of the thermal desorption rates of indium from strained GaInAs grown off a GaAs substrate. We have made these measurements by monitoring the photoluminescence (PL) of the groundstate emission from strained quantum wells. We show that this method can be an accurate and highly sensitive technique for measuring desorption rates. The measurements have been made as a function of composition and arsenic overpressure. A simple model for the indium incorporation is developed and an activation energy for the desorption process has been obtained.

Investigation of the band structure of the strained systems InGaAs/GaAs and InGaAs by high-pressure photoluminescence

InxGa1-xAs quantum wells grown pseudomorphically in GaAs and AlGaAs with values ofx up to 0.25 have been studied by photoluminescence under high hydrostatic pressure. We concentrate here on the pressure range where the emissions quench and take on the characteristics of theX-minima. In the InGaAs/GaAs structures, these transitions display an unexpected pressure coefficient, -2.6 meV/kbar, twice that of theX minima in GaAs. We assign these transitions to theX minima in the wells, and therefore make a direct measurement of the strainedX positions as a function of composition. In the InGaAs/AIGaAs structures the crossovers occur against theX-minima in the barriers and these crossovers yield an accurate value for the band offset ratio for InGaAs/GaAs heterojunctions which is found to be 60:40 (CB:VB).

Growth and characterization of relaxed epilayers of InGaAs on GaAs

Abstract We report the growth of 3 μm thick relaxed layers of In x Ga 1− x As on GaAs substrates, with x from 0.1 to 1, and give some results of compositional, optical, structural and electrical characterisation. Compositions were determined by several techniques, with results which agreed to within a Δx of ±0.02. For x above 0.2 the crystal quality is very poor. Some layers have been grown with stepped compositions up to x = 0.4 and this improves the crystal quality. We show that in the InGaAs/GaAs system there is a threshold strain, rather than threshold composition change, above which crystal quality is degraded.

Thermal interdiffusion in InGaAs/GaAs strained quantum wells as a function of doping density

Abstract We have studied the thermal stability and interdiffusion of InGaAs/GaAs single quantum wells as a function of temperature for both p-type, Be and n-type, Si doping at various doping concentrations. The interdiffusion of the group III elements is monitored using the photoluminescence from the ground states of the valence and conduction band quantum wells. The intermixing is modelled the using a Greens function method to solve the diffusion equation to describe the evolution of the well shapes during processing; the Schrodinger equation is solved for this well shape, to provide the ground state energy levels of the system using the interdiffusion constant as the only unknown fitting parameter which is therefore uniquely determined. Using this approach we have determined the Ga/In interdiffusion constants for anneal temperatures upto 1050°C for doping levels upto 10 18 cm −3 .

The effects of silicon and beryllium on the interdiffusion of GaAs/AlxGa1-xAs and InxGa1-xAs/GaAs quantum well structures

The effects of silicon and beryllium at doping levels of up to 1019 cm−3 on the interdiffusion of GaAs/AlxGa1−xAs and InxGa1−xAs/GaAs quantum wells after annealing have been studied using photoluminescence. It was found that for beryllium concentrations up to 2.5 ×1019 cm−3 and for silicon doping concentrations up to 1018 cm−3, no change in the interdiffusion coefficients could be measured. For a silicon doping concentration of 6×1018 cm−3 a dramatic degradation of the material quality was observed following annealing at 750 °C for 15 s. This resulted in the luminescence from the well disappearing and the appearance of deep level luminescence related to donor‐gallium vacancy complexes and arsenic antisite defects. From these results we suggest that the position of the Fermi level plays no role in the intermixing of III‐V heterostructures and that most of the enhanced intermixing observed in silicon‐doped GaAs/AlxGa1−xAs structures is related to silicon relocation at very high doping levels.