GAAS METAL-SEMICONDUCTOR-METAL PHOTODETECTORS (MSM-PDS) WITH ALGAAS CAP AND BUFFER LAYERS

GaAs metal-semiconductor-metal photodetectors with AlGaAs cap and buffer layers have been fabricated and studied. It is shown that the trap-induced effects which result from the GaAs surface trap states can be avoided by adding an AlGaAs cap layer. In addition, we used an AlGaAs buffer layer to reduce the interfacial charge effects between the GaAs substrate and the GaAs absorption layer. The dark currents were less than 1 nA and the low frequency internal gain was dramatically improved. The results also show that a complete depletion can occur even at biases below 0.5 V.