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/cm2 to 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.
Spatial variations of band potentials and properties of carrier recombination were examined in semipolar (2021) plane InGaN/GaN single quantum wells by scanning near-field photoluminescence (PL) spectroscopy. The quantum wells had In content from 0.11 to 0.36 and were emitting from violet to yellow-green. Near-field scans showed small PL peak energy and linewidth variations with standard deviations below 10 meV, which confirms small alloy composition variations in the quantum wells. The scans revealed large, ~5 to 10 μm size areas of similar PL parameter values, as opposed to 100 nm scale variations, often reported for InGaN wells. With increased excitation power, an untypical photoluminescence peak energy shift to lower energies was observed. The shift was attributed to density dependent carrier redistribution between nm-scale sites of different potentials. The experimental results show that in the (2021) plane InGaN quantum wells the localization potentials are shallow and the recombination properties are spatially rather uniform, which confirms the high potential of these QWs for photonic applications.