Date of Award

Winter 1995

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical & Computer Engineering

Committee Director

K. H. Schoenbach

Committee Member

A. N. Dharamsi

Abstract

The properties of transition metals in gallium arsenide have been previously investigated extensively with respect to activation energies, but little effort has been made to correlate processing parameters with electronic characteristics. Diffusion of copper in gallium arsenide is of technological importance due to the development of GaAs:Cu bistable photoconductive devices. Several techniques are demonstrated in this work to develop and characterize compensated gallium arsenide wafers. The material is created by the thermal diffusion of copper into silicon-doped GaAs. Transition metals generally form deep and shallow acceptors in GaAs, and therefore compensation is possible by material processing such that the shallow silicon donors are compensated by deep acceptors. Copper is an example of a transition metal that forms deep acceptors in GaAs, and therefore this work will focus on the compensation and characterization of GaAs:Si:Cu.

The compensation of the material has shown that the lower diffusion temperatures (500-600°C) form primarily the well-known CuB centers whereas the higher temperature anneals (>$750°C) result in the formation of CuA. Using compensation curves, the copper density is found by comparing the compensation temperature with copper solubility curves given by others. These curves also show that the formation of CuB, EL2, and CuA can be manipulated by varying processing parameters such as annealing temperature and arsenic pressure. The compensation results are confirmed using Temperature-Dependent Hall (TDH) measurements to detect the copper levels. Also, the photoconductive properties of the material under illumination from 1.06 and 2.1 μm wavelength laser pulses have been used to demonstrate the effects of the different processing procedures. The persistent photoconductivity inherent to these devices under illumination from the 1.06 μm laser pulse is used to predict the concentration of the CuB level, and the fast hole capture times of the various acceptors are found through the response to a 140 ps (FWHM), 2.1 μm laser pulse. Finally, the physical distribution of the copper atoms in the gallium arsenide wafer is examined using Glow Discharge and Secondary Ion Mass Spectroscopy (GDMS and SIMS). These techniques have been used to show that the copper diffusion in gallium arsenide is non-uniform with respect to depth and surface position.

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DOI

10.25777/6jpa-as89

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