Monolithic integration and individually-optimized operation of In/sub 0.2/Ga/sub 0.8/As vertical-cavity surface-emitting lasers and resonance-enhanced quantum well photodetectors

In high density, parallel optical interconnect applications, it is often advantageous to monolithically integrate the photonic functions on a single substrate in order to achieve improved performance and to simplify packaging. It is also desirable to have an epilayer design that can incorporate many of these functions without compromising their individual performance. The monolithic integration of the optical source and photodetection functions is demonstrated here using a VCSEL and a resonance-enhanced photodetector (REPD), which share a common multiquantum-well active region that is enclosed within two different embedded resonance cavities. Each cavity is individually optimized to provide efficient operation for both the VCSEL and the REPD. Since optimum VCSEL performance requires very high mirror reflectivities, while optimum REPD performance for a REPD requires a cavity with lower reflectivities, the use ofa single design may compromise both. In our new design, however, the cavity of the REPD is embedded within the cavity of the VCSEL, so that the former cavity can be realized by chemically removing some of the AlAs/AlGaAs quarter-wave layers in the upper DBR mirror. The REPDs have achieved quantum efficiencies as high as 85%, while the VCSELs have achieved threshold current densities as low as 850 A/cm/sup 2/ and differential quantum efficiencies as high as 50%.