Date of Award

Spring 1993

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical & Computer Engineering

Program/Concentration

Electrical Engineering

Committee Director

Vishnu K. Lakdawala

Committee Member

Glen Gerdin

Committee Member

Linda Vahala

Committee Member

Mohammad Zubair

Abstract

Diffusion of copper in silicon doped gallium arsenide under different diffusion conditions is studied. Copper compensated silicon doped gallium arsenide (GaAs:Si:Cu) is used as switch material for bulk optically controlled semiconductor switch, and on-state photoconductivity of the switch is primarily due to the properties of the copper deep levels introduced in the material during diffusion. Gallium arsenide being a compound semiconductor, presence of vacancies and defects make the study of diffusion a complex process. The objective of the current research is twofold: a) to study the influence of diffusion conditions and processing techniques on copper deep level formation in silicon doped gallium arsenide (GaAs:Si) and b) to fabricate a switch material with high photoconductive gain so that low power semiconductor lasers can be used as the excitation source for closing the switch. Influence of different diffusion parameters, in particular, arsenic vapor pressure on the diffusion of copper and copper deep level formation in GaAs:Si is studied. Three different diffusion techniques, namely, closed tube diffusion, semi-closed tube diffusion, and leaky tube diffusion are used to diffuse copper in GaAs:Si. The diffusion of copper in GaAs is studied for the first time in the present work using the leaky tube diffusion technique, and the results show that it is the best among the three techniques studied, to diffuse copper to obtain high efficiency switch material.

Photoinduced current transient spectroscopy (PICTS) and van der Pauw-Hall measurements are used to characterize the diffused samples. Various deep levels present in the diffused samples are identified and the variation of the characteristics of these levels with diffusion conditions is analyzed. PICTS spectra of GaAs:Si:Cu samples processed using different techniques are found to be strikingly different. Deep level structure at different depths from the surface of the GaAs:Si:Cu crystal annealed using the closed tube diffusion technique has been studied using the PICTS, and the results indicated the presence of a gradient in the copper related levels in the material. In leaky tube diffusion, the gradient effect is minimized by providing a source of copper on both surfaces of the sample and protecting the surfaces by silicon dioxide coating. Based on the characterization results, models for different copper related complexes have been identified, Vas CuGa VAs (arsenic vacancy is denoted as Vas and copper in gallium site is denoted as CuqJ and CuGa), and CuGa for CuB and CuA respectively. Photoconductivity of the GaAs:Si:Cu switches fabricated using the three different techniques is measured and found that switches fabricated using the leaky tube diffusion technique are the most efficient among the three. The efficiency of the leaky tube samples is high enough to use low power semiconductor laser diode as the excitation source.

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DOI

10.25777/9x80-p181

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