Fabrication and performance of GaAs p+n junction and Schottky barrier millimeter IMPATT's

A recently developed procedure, incorporating both preferential electrochemical etching for wafer thinning and electroplating for heat sink formation has been applied to the fabrication of Kaband (26.5-40 GHz) GaAs IMPATT's. Both epitaxially grown GaAs p⁺n junction and Cr Schottky barrier diodes have been fabricated. This procedure makes possible the batch fabrication of small area diodes (<2 times 10^{-5}cm²) over a large wafer area. The diodes have been operated both in the oscillator and stable-amplifier mode. Power, efficiency, and noise performance of the devices is reported. The p⁺n diodes, which could withstand junction temperature of over 300°C, gave the best power and efficiency. Powers as high as 680 mW with 12.4 percent efficiency at 34.8 GHz and an efficiency as high as 16 percent with 390 mW at 29.5 GHz have been achieved. The Cr Schottky diodes were unable to withstand junction temperatures in excess of 200°C and therefore produced less power despite the potentially better power handling capability. The highest power obtained from a Cr Schottky is 470 mW with 12.5 percent efficiency at 34 GHz. Comparable oscillator noise performance has been obtained with both types of diode. The best AM (DSB) double sideband NSR obtained is -135 dB in a 100 Hz window at 1.5 MHz from the carrier. An rms frequency deviation as low as 13 Hz in a 100 Hz window has been observed with a power output of 164 mW at 35.4 GHz by raising the external Q to 138. A lowest FM noise measure of 23 dB was achieved by reducing output power to 16 mW. The amplifier noise figure measured for both p⁺n and Cr Schottky diodes is 26 dB.