Dielectric Response of Light Emitting Semiconductor Junction Diodes: Frequency and Temperature Domain Study
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Dielectric Response of Light Emitting Semiconductor Junction Diodes: Frequency and Temperature Domain Study Kanika Bansal and Shouvik Datta Indian Institute of Science Education and Research, Pune – 411008 India.
ABSTRACT We report a change in the dielectric response of AlGaInP based multi quantum well diodes with the onset of modulated light emission. Observed variation in junction capacitance and modulated light emission, with frequency and temperature, suggests participation of slow defect channels in fast radiative recombination dynamics. Our work establishes prominent connection between electrical and optical properties of light emitting diodes and provides a tool to investigate the interesting condensed matter physics of these structures. Our observations demand a generalized physical framework, beyond conventional models, to understand an active light emitting diode under charge carrier injection. We suggest that the low frequency response can compromise the performance of these diodes under high frequency applications. We also suggest how internal quantum well structure can affect modulated light output efficiency of the device. INTRODUCTION Understanding a semiconductor junction emitting light is a challenging task. Presence of a large number of charge carriers and fast recombination process limits the use of conventional characterization techniques and understanding based on depletion approximation [1] for these devices. However, technologically and fundamentally, it can be very useful to comprehend the condensed matter physics of a semiconductor diode during light emission. With this motivation, we explored the dielectric response, as well as the modulated light emission from AlGaInP based, multi quantum well, red light emitting devices. We measured low frequency (≤ 100 kHz) impedance of these devices in different regimes of charge carrier injection [2, 3]. Simultaneously, we also measured the component of light output modulated at a particular frequency and named it voltage modulated electroluminescence or modulated light output [2, 3]. Our results show that with the onset of modulated light output at a given frequency and temperature, junction capacitance acquires inductive like behavior. To explain this remarkable connection between optical and electrical properties, we consider the participation of subbandgap defect levels in charge carrier recombination dynamics. Light emission onset causes fast recombination processes to compete with slowly responding defects, resulting in an inductive like behavior. This behavior is manifested as negative capacitance. When temperature of the device is varied, properties of this inductive like response along with the modulated light emission are governed by the change in the contribution from ‘slow’ defect channel towards fast radiative recombination. However, at temperatures high enough, internal dynamics of quantum well structure has to be considered to explain the change in the behavior of modulated light output and negative capacitance [4].
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