Date of Award

12-1995

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Engineering Physics

First Advisor

Yung Kee Yeo, PhD

Second Advisor

Robert Hengehold, PhD

Abstract

The current conduction mechanisms of 4H-SiC p+n mesa diodes were studied using current-voltage-temperature (I-V-T), capacitance-voltage-temperature (C-V-T), deep level transient spectroscopy (DLTS), optical observations, and reverse breakdown measurements. Temperature and voltage dependencies of diffusion, recombination, and tunneling current processes are shown to be consistent with Sah-Noyce-Shockley theory. Recombination currents having an ideality factor of A=1.85-2.1 yielded an activation energy of EA=1.56 eV, whereas for ideal recombination, A=2 and EA=1.6 eV. Forward I-V curves of poor diodes dominated by tunneling and recombination processes, showing low reverse breakdown voltages of approx. 100 V, can be correlated to DLTS results which show large defect concentrations, and spectral observations indicating radiative recombination via defect sites. On the other hand, well-behaved diodes exhibited a breakdown voltage at approx. 450 V, a spectral output centered at 385 µm, and recombination-to-diffusion current ratios of 1012 - 1029 that agree with theory. C-V-T, DLTS, and reverse I-V-T data revealed several defect centers. C-V-T and reverse I-V-T measurements yielded an energy level at approx. 70 and approx. 62 meV, respectively, which is possibly attributable to nitrogen donor levels. Reverse I-V-T and DLTS results, in approximately half of the diodes tested, yielded a second trap level at 173 ±19 and 150 ±34 meV, respectively. Approximately 20% of the well-behaved diodes tested were found to breakdown unexpectedly at reverse biases as low as 95 V. It is believed that this unexpected breakdown is due to nanopipe defects in the diodes.

AFIT Designator

AFIT-GAP-ENP-95D-04

DTIC Accession Number

ADA309857

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