Microwave Emission from Indium Antimonide Stimulated by Acoustic Wave Amplification

Abstract

A small‐signal theory is presented for the emission of microwave noise, stimulated by acoustic wave amplification, from n‐type InSb at 77°K in a transverse magnetic field, for electric drift fields below 25 V/cm. The acoustic gain at frequencies different from ω₀, the frequency of maximum acoustic gain, is greatest at drift fields exceeding that required for highest gain at ω₀. At these fields the gain becomes an extremely broad band phenomenon with substantial amplification occurring at frequencies an order of magnitude greater than ω₀. The presence of a transverse magnetic field has been shown to enhance the acoustic gain of a high mobility piezoelectric semiconductor, over a certain range of drift fields, by effectively reducing the rf mobility by the factor 1/[1+(μB)²]. Experimental results obtained from 700 MHz to 12 GHz have shown good agreement with the small‐signal theory, which takes into account the electric field distribution within the crystal. In particular, the threshold curves obtained at X‐band indicate that a constant value of acoustic gain is required for the production of the emission. Receivers of sensitivities around − 105 dBm were used and could detect emission only for magnetic fields exceeding 1kG, oriented close to the exactly transverse direction. Threshold fields as low as 1 V/cm were measured for the inch‐long crystals used, for which μ=500 000 and n=10¹⁴ cm⁻³ at 77°K. The conclusions drawn are that this ``low field'' emission is acoustic in origin, requires the presence of a transverse magnetic field and is a one‐carrier type phenomenon.