Strain-relaxed, high-speed In0.2Ga0.8As MQW p-i-n photodetectors grown by MBE.

We have fabricated p-i-n photodetectors with 10, 15 and 20 well Insub0.2Gasub0.8As/GaAs multiple quantum wells (MQWs) in the intrinsic region, whose bandwidths exceed 23 GHz. Cathodoluminescence (CL) images are characterized by rectangular grids, indicating strain relaxation through the formation of misfit dislocations. The MQW photoluminescence (PL) is strongly affected by the junction electric field, but PL from the phigh++ GaAs cap shows that increasing the number of QWs enhances the non-radiative recombination associated with the misfit dislocation network. Infrared absorption measurements reveal sharp, room temperature excitonic absorption at 980 nm, which shifts to 1000 nm with a 6 V reverse bias. The peak excitonic absorption intensity and linewidth improve as the number of wells increases. Room temperature dark current measurements on 250 mymx250mym p-i-n photodetectors yield leakage currents as low as 2.5 nA for a reverse bias of 4.4. V. These results demonstrate the usefulnes s of strain-relaxed InGaAs/GaAs MQW photodetectors for high speed applications.