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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 [ 11. 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 of a 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 Ncm2 and differential quantum efficiencies as high as 50%.The epilayer design of Fig. 1 allows the same epitaxial layers to be used for both the source and the photodetector. thickIn, ,Ga, 8 A~ quantum wells separated by 100 A thick GaAs barrier layers, which are bound by two compositionally-graded Al,Ga,-,As cladding layers with x graded from 0 to 0.47. This region is bounded by upper and lower DBR mirrors consisting of 24 pairs and 38.5 pairs of Al, lsG% ,As/Al, 93G% ,,AS quarter-wave layers, respectively, with biparabolically-graded hetero-interfaces and a doping level of 2 x 10l8 cmV3. A GaAs contact layer, half-wavelength thick and doped to 1 x 1019 ~m -~, forms the uppermost layer of the DBR. The active area of the VCSEL is defined by proton-implantation at 370 keV, with a dose of 3 x 1014 Improvement of the quantum efficiency of thin absorptive semiconductor layers by placing them within a resonant cavity was proposed and demonstrated by [ 2 ] . In the present design, the REPD cavity is formed in the designated detector areas by chemically removing the 13 uppermost DBR pairs from the VCSEL structure, leaving 1 1 quarter-wave pairs for the upper DBR mirror, whose top layer consists of GaAs doped to 1 x 1019 cm". The reduced Q of the REPD cavity provides resonance-enhanced absorption across a spectral window -2 nm in width, with a peak efficiency of -90%. The thin absorption region also keeps the carrier transit times short. Although this epilayer design is optimized for a top-surface-emitting (and absorbing) topology, the use of In, 2Ga, *As quantum wells allow light to be emitted or absorbed through either surface, thus providing the possibility for bi-directional optical transmission.The responsivity ...