GaAs avalanche photodiodes and the effect of rapid thermal annealing on crystalline quality of GaAs grown on Si by molecular-beam epitaxy

Photoluminescence, Rutherford backscattering/channeling, x-ray double crystal rocking curves, and minority carrier lifetime suggest that structural and optical properties of GaAs grown on Si by molecular-beam epitaxy (MBE) improve greatly as a result of postgrowth rapid thermal annealing (RTA). Transmission electron microscopy, in contrast, shows no significant reduction in defect density (∼108 cm−2) after RTA although the defect configuration is affected. Dislocations tend to organize better and combine each other after RTA. The minority carrier (electron) lifetime was found to improve from 2 to 2.7 ns as a result of RTA in p+GaAs(p>1018 cm−3). Annealing at a temperature as low as 750 °C and of a layer as thin as 0.1 μm also produces a significant improvement in photoluminescence (PL) intensity. It is suggested that in situ RTA after a short growth (∼0.1 μm) followed by the growth of the rest of the structure may result in substantial improvement in material quality. To assess the uniformity of the as-grown GaAs on Si and the presence of electrically active defects, avalanche photodiodes (APD’s) were made and tested for spatial uniformity of photoresponse with the help of a flying spot microscope. In devices with thin buffer layer (1.5 μm) microplasma were found to be formed at high reverse field. However, in devices with a thick buffer layer (3 μm) no spatial variation of avalanche gain over the whole device area or formation of microplasmas was detected at the highest reverse field applied. The avalanche gain in APD’s was rather low (∼7) and was limited by the excessive leakage current. The I–V characteristics and the device yield were found to improve significantly on a wafer which was rapidly thermal annealed prior to processing.