Date of Award

Fall 1994

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Electrical Engineering - (Ph.D.)

Department

Electrical and Computer Engineering

First Advisor

Kenneth Sohn

Second Advisor

Roy H. Cornely

Third Advisor

Walter F. Kosonocky

Fourth Advisor

Haim Grebel

Fifth Advisor

N. M. Ravindra

Abstract

The relaxation semiconductor is defined as one in which the dielectric relaxation time (τd;resistivity times permittivity) is greater than lifetime (τo). Non-hydrogenated amorphous Silicon Carbide (SiC) and KrF excimer laser induced disordered Si were used for the relaxation semiconductors. Both semiconductors have high resistivity, wide energy gap, and numerous defects. A novel diode, consisting of those semiconductors on p-type crystalline Silicon (c-Si), was fabricated. In the diode structure, an injecting contact was made on the relaxation material and a Schottky barrier contact was made on the c-Si.

Electrical characteristics of both diodes were found to have interesting effects: negative capacitance, negative resistance, space charge limited current, and bistable switching with long term memory. During the C-V measurement of a disordered Si/c-Si heterojunction diode, for the first time, a constant negative capacitance of 1520pF was observed from - 10v to 10v at 1MHz. This negative capacitance was considered as an inductive behavior. The measured inductance value was approximately 16.7 µH at 1MHz. The inductance was proportional to 1/ω2 in the variation of frequency and 14.74mH at 30KHz as measured by a LCR analyzer. In an a-SiC/c-Si heterojunction diode, a negative capacitance was also observed in both biases. The inductance value was 36µH above 3.5v and below 3.5v at 1MHz. The shape of negative capacitance between - 3.5v and 3.5v was parabolic and the inductance, near zero bias, was 30µH. The inductance was almost constant between 1MHz and 30KHz.

An inductive part of the heterojunction diode was derived theoretically using the relaxation theory and Shockley theory. The inductance was either constant if ωτd < 1, or proportional to 1/ω2 ωτd > 1. Moreover, a circuit model of the heterojunction diode was also developed. The negative capacitance, Ctest showed |Ctest| = 1/ω2 Ltest at the circuit model. Computer simulation also showed negative capacitance similar to that of the experiment.

It was proposed that conductivity modulation, by carrier injection in a thin relaxation semiconductor, causes an inductive behavior, and the relaxation would be more pronounced by the carrier screening of impurities. The novel heterojunction diode may replace a physical inductor in microelectronics.

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