Multiple Quantum Barrier Avalanche Photodiode Based on GaN/AlGaN Heterostructures for Long Wavelength Infrared Detection

A multiple quantum barrier (MQB) avalanche photodiode (APD) structure based on GaN/AlxGa $_{1{-}x}\text{N}$ material system has been proposed in this paper which is capable of detecting infrared (IR) signal up to $6.0~\mu \text{m}$ wavelength. A self-consistent quantum drift-diffusion (SCQDD) model developed by the authors, has been used to determine the current-voltage characteristics under dark and illuminated conditions, spectral response, excess noise properties, signal-to-noise ratio, time and frequency responses. Results show that the proposed MQB APD attains peak responsivity of 60 AW $^{-1}$ at $3.0\, \mu \text{m}$ wavelength. Incorporation of a dedicated thin $n$ -type GaN layer for avalanche multiplication in between the $p^{+}$ -GaN contact layer and MQB constant-field drift-layer ensures significantly low noise equivalent power under normal operating conditions at room temperature (300 K). Optical pulse response of the device reveals that special restriction over the charge multiplication able to supress the minor peaks of the current response and consequently significantly narrow pulse response can be achieved. Narrow pulse response leads to broad bandwidth of 274.5 GHz, which is significantly broader than the existing IR photo-detectors.