Microwave amplification in a GaAs bulk semiconductor

Abstract

Continuous linear microwave amplification has been obtained using <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</tex> -type GaAs at room temperature. Amplification of signals in the 2 to 10 Gc/s range occurred when a dc field applied across semiconductor wafers mounted in a conventional reflection type amplifier circuit exceeded about 3100 volts/cm. Ohmic contacts were applied to wafers 125 µ square and 40 to 120 µ thick. The resistivity varied between 10 and 120 ohm-era. The <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n \cdot L</tex> product in amplifying samples did not exceed 5.10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> . The conductance measured in the 1 to 10 Gc/s region was found in some samples to be negative over a frequency range of one octave. Other samples exhibited negative conductance (i.e., gain) only over a few hundred megacycles. Each sample showed a peak gain accompanied by a range of absorption at the high-frequency end of the negative conductance region. The differential conductance at dc was positive. An amplifier noise figure of 23 dB was measured using 120 ohm-era GaAs at 10 dB gain and 1 dB of gain compression occurred when the output power level reached -6 dBm.