Picosecond photoconductivity in polycrystalline gallium arsenide grown by molecular beam epitaxy

Picosecond photoconductivity in polycrystalline gallium arsenide (GaAs) layers grown on silicon dioxide by molecular beam epitaxy has been investigated. Photocurrent transient responses having full width at half-maximum of ∼2.2 ps were measured by photoconductive sampling techniques. Interdigitated metal-semiconductor-metal photodiodes have been fabricated from the polycrystalline GaAs with 1.5- and 5-μm electrode spacing. The corresponding responsivities measured are 40 mA/W and 0.15 A/W, respectively, at 10 V/μm bias voltage and 820-nm wavelength. The corresponding effective mobility of this material is estimated to be μeff∼80 cm2/V s, making this photodetector competitive with alternative technologies for ultrahigh speed applications.