Low temperature growth of GaAs on Si substrates for ultra-fast photoconductive switches

We have grown GaAs directly on silicon substrates by molecular beam epitaxy (MBE) at low substrate temperatures (similar to250 degreesC). The silicon wafer surface cleaning and GaAs film growth processes were done at temperatures lower than the Si-Al eutectic temperature, in order to enable monolithic integration of low-temperature-grown-GaAs (LT-GaAs) photoconductive switches with Si-CMOS circuits. In situ reflection high-energy electron diffraction (RHEED), ex situ x-ray diffraction (XRD) and atomic force microscopy (AFM) studies were performed to characterize the LT-GaAs film quality. The film surfaces show less than 1 nm root-mean-square (rms) roughness and the anti-phase domain (APD) density is below the XRD detection limit. Metal-semiconductor-metal (MSM) photoconductive switches were made using this material. A time-resolved electro-optic sampling technique was used to determine the responsivity and speed of the switches. A full-width at half-maximum (FWHM) switching time of similar to2 picoseconds was achieved and the responsivity of switches made from LT-GaAs on Si material was comparable to that of switches made from LT-GaAs on GaAs material.