Low Temperature Growth of GaAs on Si Substrates for Ultra-fast Photoconductive Switches

摘要

We have grown GaAs directly on silicon substrates by molecular beam epitaxy (MBE) at low substrate temperatures (～250 ℃). 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 ～2 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.