Date of Award

3-2002

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Engineering Physics

First Advisor

Michael B. Scott, PhD

Abstract

Epitaxial n-type 4H-silicon carbide (SiC) is irradiated with 2 MeV protons to evaluate the dislocation damage effects on the optical and electrical characteristics of the material. Semiconductor materials with a high tolerance to radiation fields have applications in several aerospace power and satellite systems. SiC is under investigation due to its potential for such space material applications. The optical properties of the material are investigated using temperature-dependent photoluminescence (PL) and the effects of proton irradiation on the electrical properties are evaluated using current-voltage measurements and constant-voltage deep level transient spectroscopy (CV-DLTS). Subsequent high-temperature thermal annealing and recovery of the irradiated material is investigated over the temperature range of 900 – 1500 °C. Proton-induced irradiation damage is apparent in the 4H-SiC material, affecting both the optical and electrical characteristics of the devices. The radiative behavior of the nitrogen-related near band edge transitions is significantly reduced as a result of the irradiation with partial recovery observed after high-temperature thermal annealing at 1500 °C. A deeper trapping complex (EC-ET ≅ 380 meV) is detected as a result of irradiation and shows signs of activation due to thermal annealing. Initial indications taken from I-V measurements of the Schottky diodes reveal that proton irradiation followed by thermal annealing at 900 °C may, in fact, enhance the rectifying device characteristics. Increasing the anneal temperature (TA = 1300 °C) causes the device to fail entirely. Further annealing of the irradiated 4H-SiC at 1500 °C demonstrates recovery in the rectifying behavior of the material. Significant levels of deep level donor traps are observed, induced by irradiation in n-type material. Three detectable defect pairs emerge with energy levels ranging from 570 – 730 meV below the conduction band. The trap parameters were determined using curve-fitting algorithms. Upon high-temperature thermal annealing of the material, the trap center pairs showed little change in the energy levels and capture cross-sections while the density of traps decreased as temperatures increased. Full recovery of the material characteristics is not apparent after annealing at 1500 °C.

AFIT Designator

AFIT-GNE-ENP-02M-01

DTIC Accession Number

ADA407806

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