Structural characterization of pseudo-insulators for gallium arsenide based devices

Vadali Mahadev, Purdue University

Abstract

The absence of a good passivating material for GaAs has been the chief problem for its use in devices. Among others, lattice-matched (Al,Ga)As, ZnSe and GaAs grown at low temperatures (LT-GaAs) have been quite successful. Structural phenomena in the GaAs/ZnSe and GaAs/LT-GaAs films were studied, to understand the influence of the interface on the electrical behavior, using high resolution x-ray diffraction. LT-GaAs grown at 225$\sp\circ$C was non-stoichiometric and exhibited a 0.15% lattice mismatch. On annealing, arsenic clusters formed and reduced the lattice strain. The arsenic precipitation corresponds to a classical case of diffusion controlled nucleation and growth followed by coarsening. While the type of dopant did not have any effect on the kinetics of arsenic precipitation in single layer films, the presence of junctions in p-n superlattices accelerated the kinetics and is in agreement with the existing charge-based model. Grazing incidence x-ray diffraction technique was used to study the buried interface structure in the ZnSe/GaAs heterostructures for varying Ga surface concentrations. Broad diffuse diffraction peaks were observed only in the Ga rich cases, and were consistent with a tetragonaly distorted Ga$\sb2$Se$\sb3$ interfacial layer. Using an ab initio total energy simulation with norm conserving pseudopotentials the Ga$\sb2$Se$\sb3$ phase was shown to be the most stable structure at the interface. And, the model indicated that the energy decreased with the relaxation of the lattice along the growth direction. The lowest energy configuration predicted by the model corresponds to an interface structure consistent with the experimental results.

Degree

Ph.D.

Advisors

Liedl, Purdue University.

Subject Area

Materials science

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