Semester

Spring

Date of Graduation

2007

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Lane Department of Computer Science and Electrical Engineering

Committee Chair

Dimitris Korakakis

Committee Member

Thomas H. Myers

Committee Member

Lawrence A. Hornak

Committee Member

Charter D. Stinespring

Committee Member

Xian-an Cao

Abstract

Bi was investigated as a possible surfactant for growth of GaAs1-xNx layers on (100) GaAs substrates by molecular beam epitaxy using an RF plasma nitrogen source. Bi extends the useable growth conditions producing smoother surfaces to a significantly higher N content than without Bi. The conductivity of Be-doped GaAsN decreased significantly with increasing N concentration. Temperature dependent Hall measurement suggests possible compensation and increased activation energy. SIMS and Raman measurements indicate that the N composition increased by introducing Be, and for low [N], Bi. The addition of Bi during growth of Be-doped GaAsN only produced semi-insulating layers.

GaAs1-xNx layers and quantum dot-like structures were grown on (100) GaAs substrates by molecular beam epitaxy. The dependence of photoluminescence emission spectra on annealing temperature is consistent with literature at lower temperatures but after annealing at 750 ºC a net red-shift is consistently observed. X-ray photoelectron spectroscopy measurements indicate that for different annealing times and temperatures, the nitrogen and arsenic surface concentrations changed compared to that of as-grown samples, specifically arsenic is lost from the material. Raman measurements are consistent with the trends in photoluminescence and also suggest the loss of arsenic occurs at higher annealing temperatures in both samples capped with GaAs and uncapped samples.

The real substrate temperature preliminarily estimated by pyrometer measurement was further verified and determined by RHEED pattern transition. RHEED was also employed to observe the surface reconstruction. To optimize growth conditions, surface phase diagrams of As4/Ga BEP flux vs. the real substrate temperature under fixed As4 BEP ~4.5x10-6 Torr and fixed growth rate 0.46 μm/hr (0.45ML/s) were obtained.

Different aperture plates of RF-plasma nitrogen discharge tube were used. Only the one with 10 x Ø0.2mm holes is able to produce streaky RHEED patterns under some growth circumstances, and was eventually selected to lead nitrogen species through for all growths in this work. Ga flux, N flow rate, and RF power were all found to be critical factors affecting the resultant N concentrations.

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