Gain and Dark Current Studies on Planar Photodetectors Made on Annealed GaAs-on-Si

Interdigital, planar photodetectors were fabricated from annealed GaAs/Si heterostructures grown by molecular beam epitaxy using alloyed AuGe/Ni and non-alloyed Cr/Au contacts. The dark current and optical gain of the Cr/Au devices is higher than that of the AuGe/Ni devices. Contact degradation due to annealing and a p-like background doping consistently explains our data. The gain-optical power relationship follows a power law with an exponent close to -1