Abstract
To examine the critical role of electrically active defects and surface states in InGaN/GaN multiple quantum well (MQW) ultraviolet photodetectors (UV-PDs), the study of degradation mechanisms in such devices is very important. In this work, we have fabricated InGaN/GaN MQW UV-PDs with a thick passivation layer of Al2O3 and studied their degradation behaviors by applying high current stress. The origin of degradation processes has been investigated intensively by employing different combined optical and electrical measurements. As a consequence of stress, we noticed that (i) the electroluminescence intensity decreases distinctly (∼ 48 %), suggesting that more of the charge carriers are captured by the newly induced defects in the active region; (ii) the open circuit voltage is mostly accountable for the degradation of photovoltaic properties in treated PDs; (iii) the parasitic current leakage paths increase significantly which in turn reduce the photocurrent generation process largely; (iv) within the temperature range of 100–440 K, the values of the ideality factor and barrier height are found to be always higher and lower in treated PDs, respectively, indicating the presence of generation-recombination centers caused by defects; (v) two major trap levels are identified in treated PDs via Laplace deep level transient spectroscopy analysis; and (vi) the responsivity in treated PDs decreases. The obtained results indicate that degradation is mainly associated with the newly generated defects, mostly Mg-related shallow acceptors, including MgGa and Mg-H2 complexes, which can form the acceptor levels as a result of the breaking of Mg-H chemical complexes due to high heating levels during the stress treatment.
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•Degradation characteristics of InGaN/GaN MQW UV photodetectors are studied.•Two major trap levels are detected in stressed PDs via Laplace deep level transient spectroscopy analysis.•Newly induced defects in the active region play an important role in worsening the device performances.•Degradation is mostly associated with Mg-related shallow acceptors, including MgGa and Mg-H2 chemical complexes.