Interdigitated electrode and coplanar waveguide InAlAs/InGaAs MSM photodetectors grown by LP MOVPE

The authors report on the layout and performance of interdigitated electrode and coplanar waveguide metal-semiconductor-metal (MSM) photodetectors based on the InAlAs/InGaAs material system and grown by low pressure metal-organic vapor phase epitaxy (LP-MOCVD). Both the low-capacitance interdigitated electrode and the impedance-matched coplanar waveguide structure exhibit a dynamic behavior with 35-ps rising time, but with a slow turn-off behavior (full width at half maximum=225 ps), which is determined by the transit time of the photogenerated carriers. The coplanar waveguide has an active area of 1.6*10/sup -3/ cm/sup 2/ and a space charge capacitance of 200 pF. The results for this waveguide demonstrate that an impedance-matched large-area device may work without RC-limitation. Using this concept, high-speed operation is no longer limited to small-area devices.<>