Sensitivity Enhancement of Metal– Semiconductor –Metal Photodetectors on Low-Temperature-Grown GaAs Using Alloyed Contacts

We have fabricated and characterized metal– semiconductor–metal (MSM) photodetectors based on low- temperature-grown GaAs with alloyed (i.e., ohmic-type) contacts. The annealed contacts optimize the electric field distribution inside the photodetector structure which results in an up-to-200% responsivity increase of the devices, compared to conventional MSM detectors with standard nonalloyed (Schottky-type) metallization fabricated on identical material. The improved MSM device with alloyed contacts shows more than three times larger output amplitude at illumination with a 100-fs Ti : sapphire laser, compared to the nonalloyed devices, without degradation of detector speed.