III-Nitride Phototransistors Fabricated on a Light-Emitting-Diode Epitaxial Wafer

Instead of using a wafer with a bipolar junction transistor n-p-n epitaxial structure, we successfully fabricated AlGaInN-based near-ultraviolet (UV) heterojunction phototransistors (HPTs) on a commercial wafer with a light-emitting-diode (LED) epitaxial structure by employing silicon diffusion to convert a part of the p-AlGaN layer into an n-AlGaN layer. High responsivity of more than 77 A/W in the near-UV spectral range, including a peak responsivity of 120 A/W at 382 nm, was obtained at a bias voltage of only 3 V. The corresponding photocurrent gain was approximately 790. The response speed and photocurrent versus incident light intensity were also characterized. The results indicate that the LEDs can be monolithically integrated with high-responsivity HPTs.