Microwave phenomena in bulk GaAs

CW microwave oscillations were generated at room temperature by using -GaAs with a carrier concentration 10¹³- 10¹⁴per cc. Fundamental frequencies between 1 - 10 kMc were excited, and harmonic signals up to 21 kMc were detected. The maximum power output and efficiency on CW basis were 56 mW and 5.2 percent, respectively, at 2 - 3 kMc. A study was made of harmonic content, linewidth, circuit and electronic tunability, as well as the effects of sample thickness, bias voltage, and temperature, on the observed signal frequency. For sample length × carrier concentration products between 2×10¹⁰- 2 × 10¹²cm^-2there was a wide diversity in behavior observed in different samples. This was tentatively attributed to the possibility of exciting not only traveling dipole domains but also growing space-charge waves. These growing space-charge waves were found to exist in samples where the condition nl < 2 × 10¹²cm^-2was satisfied, and are also suspected of being responsible for the observed microwave amplification in bulk GaAs. Three different contacts were used successfully: nickeltin, indium-nickel, and indium-gold. These contacts, and the general semiconductor preparation techniques, will be described in detail.