David L. Peterson

Properties of Ga vacancies in AlGaAs materials

Intermixing of AlGaAs‐based interfaces is known to be enhanced by capping wafers with a layer of SiO2. Assuming that this enhancement results from the introduction of additional Ga vacancies into the sample, it is possible to obtain the temperature‐dependent equilibrium Ga vacancy diffusivity. Experiments are performed whereby SiO2‐capped quantum well samples are annealed at temperatures ranging from 800 to 1025 °C. Calculated photoluminescence shifts are compared with the measured spectra, and a relation for the Ga vacancy diffusivity of the form 0.962 exp(−2.72/kBT) cm2/s is obtained. Using this relation, the equilibrium Ga vacancy concentration can be computed via an ensemble Monte Carlo simulation. The resulting expression is 1.25×1031 exp(−3.28/kBT) cm−3.

Effect of ion implantation dose on the interdiffusion of GaAs‐AlGaAs interfaces

Experimental results of enhanced interdiffusion of GaAs‐AlGaAs interfaces are reported. These are obtained by implanting Ar ions at doses ranging from 2×1013 to 5×1014 cm−2 into heterostructure samples followed by rapid thermal annealing at 950 °C for 30 s. The degree of intermixing decreases from the surface up to the projected ion range and is a function of the implantation dose. It is postulated that this variation results from the coalescence of some of the excess vacancies into extended defects, which are then unavailable to assist in the enhanced interdiffusion process. By assuming that the concentration of mobile vacancies at any depth is proportional to the ion’s electronic energy loss and inversely proportional to the ion’s nuclear energy loss, the calculated intermixing results are shown to be in good agreement with the experimental data.

Diffusion of Ga Vacancies and Si in GaAs

Using the Si-pair diffusion formalism of Greiner and Gibbons, a new Si diffusion model is developed based on the dominant diffusion species being Si Ga + - V Ga - pairs, where V Ga is the Ga vacancy. In the model, the unknown parameters are the pair diffusion coefficient (D p ) and the equilibrium constant, which are fitted to the experimental data. D p is also derived to be equal to one-half the Ga vacancy diffusivity. To verify this relation, an experiment to determine the V Ga diffusivity, D v , is performed. A relation for D v of the form 0.962 exp(-2.72 eV/kT) cm 2 /s is obtained, and it is shown that the fitted D p values are indeed approximately equal to 0.5 D v .

Enhanced Interdiffusion of GaAs-AlgaAs Interfaces Following Ion Implantation and Rapid Thermal Annealing

The interdiffusion of GaAs-AlGaAs interfaces has been shown to be enhanced following ion implantation and rapid thermal annealing at approximately 950°C. A model is presented which explains this phenomenon. It is based on the solution of coupled diffusion equations involving the excess vacancy and Al distributions following ion implantation. Both initial distributions are obtained from the solution of a three-dimensional Monte Carlo simulation of ion implantation into a heterostructure sample. The model is found to be in excellent agreement with several sets of experimental data. More specifically, the model is shown to be valid for ions which do not diffuse appreciably in the time frame of the rapid thermal annealing and for as-implanted vacancy concentrations below ∼6×10 19 cm −3 . Above that concentration, some vacancies are hypothesized to coalesce, thus being unavailable to assist in the enhanced interdiffusion process.