Nonradiative recombination mechanisms in InGaN/GaN-based light-emitting diodes investigated by temperature-dependent measurements

Abstract

Two kinds of InGaN-based light-emitting diodes (LEDs) are investigated to understand the nonradiative carrier recombination processes. Various temperature-dependent measurements such as external quantum efficiency, current-voltage, and electroluminescence spectra are utilized from 50 to 300 K. Based on these experimental results, we analyze the dominant nonradiative recombination mechanism for each LED device. We also analyze the effect of the dominant nonradiative recombination mechanism on the efficiency droop. On the basis of correlation between the efficiency droop and nonradiative recombination mechanisms, we discuss an approach to reducing the efficiency droop for each LED device.

The Effect of Imbalanced Carrier Transport on the Efficiency Droop in GaInN-Based Blue and Green Light-Emitting Diodes

“…The green LEDs that have lower p p0 , µ p , and a higher δ value than the blue LEDs' counterparts should have not only a larger C DL , but also a lower J Onset-of-droop , according to Equations (1) and (2). The onset of the efficiency droop is observed at current densities of 2.96 A/cm 2 for the blue LED and 0.33 A/cm 2 for the green LED, consistent with our expectation, and with results reported in the technical literature [26][27][28][29]. It is worthwhile to note that the green LEDs typically have a higher SRH non-radiative recombination coefficient A SRH than the blue LEDs, because of more defect sites in the epitaxial films caused by the larger lattice mismatch between the GaInN well and GaN barrier [30].…”

Impact of superlinear defect-related recombination on LED performance at low injection

“…22 SRH recombination can also be thermally activated, such that the SRH mechanism is frozen out at low temperature. 18 Indeed, for T , 50 K, we observe a temperature-independent IQE response curve that asymptotically approaches a consistent maximum level with decreasing current density J. Asymptotic IQE response indicates that nonradiative mechanisms are becoming less and less competitive with the radiative process at low injection. These observations, which are generally consistent with other studies, 20 further justify our normalization procedure.…”

“…For this type of experiment, low duty cycle pulsed-current operation is generally preferred to minimize self-heating in the device. 18 Nevertheless, our EL signal is obtained in a quasi-steady-state condition to better approximate normal operation and to maintain compatibility with complementary imaging measurements, which have been reported separately. 19 We activate the current output on the SourceMeter, record the photoreceiver voltage, and then deactivate the current output.…”

Influence of carrier overflow on the forward-voltage characteristics of InGaN-based light-emitting diodes

“…On a linear scale, it is observed that the efficiency droop becomes severer as temperature is lowered from 300 K. These behaviors are explained as follows: (i) The freeze-out of the Shockley-Read-Hall (SRH) process in the active MQWs region plays a leading role at low driving currents in increasing the overall EQE as temperature is lowered. 7 (ii) The increase in efficiency droop with decreasing temperature results from the increase in carrier overflow to the p-GaN layer caused by the saturation of the radiative recombination rate in MQWs. [10][11][12] Figure 2 shows the EL spectra measured at 100 mA under different temperatures.…”

“…[7][8][9][10][11] There are several reports that the carrier overflow to the p-GaN layer plays an important role in room-temperature and lowtemperature efficiency droop. In particular, the carrier recombination in the p-GaN layer by carrier overflow becomes more crucial as the increase in driving current and the decrease in temperature occur in InGaN-based blue and green LEDs and even in AlGaInP-based red LEDs.…”