Degradation and recovery of high-periodicity InGaN/GaN MQWs under optical stress in short-circuit condition

We present an investigation on the stability of high periodicity (30 pairs) multiple quantum well InGaN-GaN devices for photodetection and light harvesting in the UV and visible spectral range. The devices under test were characterized during optical stress by I-V measurements in dark condition and illuminated with a monochromatic LD emitting at 405 nm with intensities ranging from 1 mW/cm2to 50 W/cm2. We submitted the devices to several step-stress experiments: a first one in short-circuit condition at 100 °C baseplate temperature with monochromatic excitation from 361 W/cm2 to 1164 W/cm2; a second one at fixed optical power of 589 W/cm2 and baseplate temperature increasing from 35°C to 175 °C. We also evaluated the carrier flow induced degradation by means of a current stress, ranging from 1 A/cm2 to 14 A/cm2, without optical excitation. We then performed a 50 hours stress at 175 °C baseplate temperature and 589.3 W/cm2 excitation. During this stress the open-circuit voltage and the optical-to-electrical conversion efficiency significantly decreased, especially at low characterization intensities, whereas short-circuit current and external quantum efficiency showed almost no variation.