Monolithic integration of GaN-based phototransistors and light-emitting diodes

Monolithic integration of GaN-based phototransistors and light-emitting diodes (LEDs) is reported. Starting with an LED epitaxial wafer, selective Si diffusion was performed to produce an n-p-i-n structure for the phototransistor. A traditional AlGaN bulk electron-blocking layer (EBL) can block electron injection from an emitter to a collector, thereby hindering the photocurrent amplification process. We used an LED wafer with a superlattice EBL; blocking can be removed under a bias of approximately 7 V and above. External quantum efficiencies of more than 100% and 600% at approximately 380 nm and 330 nm, respectively, were achieved at room temperature and a bias of 11 V, corresponding to responsivities of 0.31 and 1.6 A/W, respectively, significantly higher than commercially available ultraviolet (UV) detectors. Furthermore, we demonstrated an integrated operation of the device. UV light was detected using a phototransistor that sent signals to drive an integrated LED as an indicator.