Thermodynamic analysis of GaInN-based light-emitting diodes operated by quasi-resonant optical excitation

Abstract

In this study, we aim to understand the thermodynamics inside the junctions of GaInN-based LEDs through optical operation of the device (the wavelength of the pumping laser is 405 nm for quasi-resonant optical excitation). First, to achieve this goal, the short-circuit current vs the open-circuit voltage curve and photoluminescence spectrum are carefully analyzed and compared with the current–voltage curve and electroluminescence spectrum. By this comparative study, we experimentally demonstrate the electrical–optical energy conversion efficiency (ECE) > 100% under optical excitation. Second, the intra-band phonon absorption and emission inside and/or outside the junction (PPeltier and PHC) are investigated through the power-loss analysis. In so doing, we ascertain that the carriers in the multiple quantum wells are energized by phonons, which introduces the ECE > 100%. Specifically, after the energization, the Boltzmann carrier distribution is no longer controlled by the ambient lattice temperature but by higher temperature, namely, that of the carriers themselves. Based on the analysis, we propose a thermally enhanced effective temperature for the Boltzmann distribution. Finally, we compare the junction efficiency by photoluminescence (PL), composed of the internal quantum efficiency by PL and the ECE by PL, of the sample at various temperatures to investigate the effect of PHC on the overall PL efficiency.

Origin of the High Forward Voltage and Low Voltage Efficiency of GaN-Based Light-Emitting Diodes at Cryogenic Temperatures

“…Figure shows the VEs from the EL (lines) and from the PL (symbols) at temperatures from 300 to 100 K. It is seen that the VE decreases as (i) the injection current increases and (ii) the temperature decreases. The VE at low currents can be greater than unity since the carriers can obtain energy from the environment . The fact that the VE at a higher temperature is higher than the one at a lower temperature indicates that the thermal energy from the environment can assist the carrier injection, thus leading to a VE greater than unity.…”

“…The VE at low currents can be greater than unity since the carriers can obtain energy from the environment. 22 The fact that the VE at a higher temperature is higher than the one at a lower temperature indicates that the thermal energy from the environment can assist the carrier injection, thus leading to a VE greater than unity. On the other hand, the comparison between the VEs obtained from the EL and the PL suggests that the decrease in VE at high injection currents is mainly caused by the additional potential drop outside the active region, caused by the transport.…”

Pre-trimethylindium Flow Treatment of GaInN/GaN Quantum Wells to Suppress Surface Defect Incorporation and Improve Efficiency

“…Next, the two-dimensional (2D) mapping data for the PL peak wavelengths (λ PL,peak ) and the integrated PL intensities of LEDs 0–5 were measured, where a 405 nm continuous-wave laser was utilized as a pumping source for the quasi-resonant excitation of MQWs Figure a shows the statistical analysis results of the 2D mapping data for λ PL,peak and integrated PL intensities of LEDs 0–5 (2D mapping data not shown here).…”

Comparative study of III-phosphide- and III-nitride-based light-emitting diodes: understanding the factors limiting efficiency

“…To understand and elucidate the limit of the IQE, understanding the carrier dynamics is key as the two are closely related. Recently, a method for investigating the net carrier movement in semiconductor heterojunction structures via thermodynamic analyses was proposed [31,32]. According to previous reports, the Peltier heating/cooling power (P Peltier ) is an indicator demonstrating the net carrier movement and dynamics.…”

“…Using this method, the net movement of the charge carriers under electrical operation can be inferred from the measured P Peltier and its dependence on J. It should be noted that the P Peltier predominantly represents a net movement of the charge carriers in the MQW active region since the P Peltier in LEDs exhibits the same carrier density-dependent behavior under resonant optical operation as that observed under electrical operation [31]. The P Peltier in LEDs is expressed in terms of the element efficiencies as follows [19,28]:…”