High-performance GaAs metal-semiconductor-metal photodetectors grown at intermediate temperatures

Planar metal-semiconductor-metal (MSM) devices fabricated on gallium arsenide (GaAs) are promising candidates for use as photodetectors in coherent optical communications and millimeter-wave phased-array applications. Their primary features are broad bandwidth, large responsivity, high power-handling capability, and compatibility with monolithic optoelectronic integrated circuits. We have characterized the performance of an interdigitated GaAs MSM photodetector grown by molecular beam epitaxy at 350 degree(s)C using a fast sampling technique in the time domain. A key factor for undoped GaAs material grown at this temperature is the optimal combination of both low dark current and high photocurrent. Experimental measurements are made of the temporal response of the MSM detector to optical impulses generated by a mode-locked titanium-sapphire (Ti:Al 2 O 3 ) laser. Speed and responsivity are characterized over a range of optical powers and DC bias voltages. Results demonstrate that this device can switch up to 69% of the applied DC bias voltage under high optical pulsed power. Results also indicate responsivities exceeding 80 mV/pJ and bandwidths approaching 20 GHz. This high-efficiency, broad-bandwidth photodetector may find critical applications in the optical production of millimeter-wave signals by frequency conversion (mixing) and harmonic generation.