Random Telegraph Signal Noise in High‐Gain SWIR Heterojunction Phototransistors

ABSTRACT InP/InGaAs‐based heterojunction phototransistors (HPTs) are promising for ultrasensitive short‐wave infrared (SWIR) detection due to their high internal gain, low excess noise, and low power consumption. This work demonstrates an HPT achieving a high optical gain of ∼1200 at −2 V bias, with dark current lower than state‐of‐the‐art avalanche photodiodes (APD). To further push its sensitivity to the limit for weak light/ultra‐long‐distance imaging, the noise mechanism in low frequency (LF) regime and its origins have been investigated, by which generation current in depletion region caused by the defect‐related traps is explored and studied. In particular, the LF noise power is found to be independent of the internal gain. A Hooge's constant of 2.1 × 10 −5 is reported for the first time in gain‐based detectors, comparable to HgCdTe devices. Remarkably, temperature‐dependent multi‐level random telegraph signal (RTS) analysis reveals two dominant origins of the generation current, corresponding to relaxation processes of two typical types of mid‐gap traps. One is Zn‐related extrinsic defects caused by Zn diffusion into the InP emitter, while the other is Ga‐related intrinsic defects in InGaAs collector. As the guideline for optimizing the HPT detector design, this work paves the way to further improve the sensitivity for low‐flux SWIR photodetection.