Low-frequency noise characterizations of GaN-based visible-blind UV detectors fabricated using a double buffer layer structure

摘要

In this paper we report systematic reliability studies of GaN UV detectors exposed to high power UV radiation. GaN epitaxial layers are deposited by rf plasma-assisted molecular beam epitaxy (MBE) utilizing a double buffer layer structure. Our studies show that the optimal buffer layer structure consists of a conventional A1N high-temperature buffer layer (HTBL) and an 800 nm thick GaN intermediate temperature buffer layer (ITBL) deposited at 690℃. Two types of devices are being investigated. Type Ⅰ devices were fabricated on the optimal double buffer layer structure. Type Ⅱ devices have only a conventional A1N buffer layer. Flicker noise measurement is used to monitor the degradation of the device due to optical stress. In addition, Ⅰ-Ⅴ and responsivity measurements were also performed. The experimental results are consistent with each other which show that the degradation of the devices arises from the generation of crystalline defects at the Schottky junction due to the exposure of the devices to the high power UV radiation. Both types of devices demonstrate degradation in their optoelectronic properties. However, while type Ⅰ devices general exhibit gradual and slow degradations type Ⅱ devices exhibit catastrophic breakdowns in the device characteristics. Our experimental data show that visible-blind UV detectors fabricated on the optimized double buffer layer structure indicate significant improvements in the radiation hardness of the devices.