InP based double heterojunction phototransistor with graded emitter-base junction and base-collector junction

摘要

Near-infrared detection has a lot of application in the fields of telecommunication, bio-sensing, environmental gas detection and hyper-spectral spectrometer. Phototransistor is one of the most promising photodetection devices that can provide integrated photo current gain even at high-speed operating conditions. A double heterojunction phototransistor was grown by molecular beam epitaxy (MBE) and fabricated on semi-insulating InP substrate. The collector-up device structure consists of InP emitter, InGaAs base, InAlAs collector and subcollector, InGaAs/InAlAs superlattice graded emitter-base (EB) and base-collector (BC) junctions. A solid GaP source was used to clean the InP substrate and grow InP buffer and emitter layer. In-situ Reflective High-Energy Electron Diffraction (RHEED) and ex-situ X-Ray Diffraction (XRD) were utilized to monitor the material growth for lattice match condition of InGaAs and InAlAs to InP substrate. A digital-alloy MBE growth technique was applied to implement the graded interfacial layers of EB junction and BC junction. The performance of the device was characterized, including current-voltage characteristics, breakdown and responsivity at the wavelength of 1.55um (telecommunication application). Simple model of phototransistor current gain with different device parameters and various operating conditions was developed and applied to the device design for hyper-spectral spectrometer application.