Date of Graduation

2008

Document Type

Thesis

Degree Type

MS

Committee Chair

Xian-An Cao

Abstract

The focus of this thesis is the electrical effects and thermal stability of plasma damage in AlGaN alloys. The effects of surface treatment using Ar and Cl2 /BCl3 inductively coupled plasmas on the rectifying characteristics of Pt/Au contacts to AlxGa1−xN (x=0– 0.5) were investigated. Plasma treatment increased the conductivity of GaN and Al0.1Ga0.9N surfaces, making the rectifying contacts into Ohmic contacts. For higher Al­ content AlGaN, the Schottky diodes turned leaky after Cl2 /BCl3 plasma treatment, where damage creation and etching occur simultaneously, whereas the diodes become more rectifying upon Ar plasma exposure, in which plasma damage accumulates. A time­ dependent study of Ar plasma treatment supports the hypothesis that the energy level of plasma damage in high­Al content AlGaN may be damage density dependent, and damage accumulation during Ar plasma exposure results in a high­resistivity region compensated by deep­level defect states. Further, the thermal stability of as­grown and plasma­treated AlxGa1−xN (x=0–0.5) has been studied. High temperature annealing up to 800 0 C in N2 ambient after plasma treatment produced significant recovery of the I­V characteristics of Schottky diodes while at temperatures higher than 800 0 C, the characteristics were degraded due to preferential surface loss of nitrogen and localized surface dissociation. A more complete removal of plasma damage in AlGaN requires annealing at temperatures >800 0 C with a careful surface protection. Schottky contacts formed on as­grown AlGaN samples subjected to high temperature annealing in an Ar ambient show improvement in the electrical characteristics up to 800 0 C. After annealing at higher temperatures, the GaN Schottky diodes became leakier, whereas the AlGaN diodes were more rectifying, confirming that N vacancies are shallow donors in GaN, but act as deep­level states in high­Al AlGaN. These new findings emphasize the need to reduce plasma damage introduced during etching processes required to fabricate AlGaN­based electronic and optoelectronic devices.

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