Understanding Microscopic Properties of Light‐Emitting Diodes from Macroscopic Characterization: Ideality Factor, S‐parameter, and Internal Quantum Efficiency

Abstract

Herein, how the macroscopic characterizations can be utilized to extract information on the defect level and crystal quality of the epitaxial layers of the light‐emitting diodes (LEDs) is presented. After review of the current–voltage (I–V) and light output power–current (L–I) characteristics, actual examples are utilized to show how different defect levels in the devices are reflected in macroscopic characteristics including the internal quantum efficiency (IQE). We show that the ideality factor from the I–V and the S‐parameter from the L–I can serve as useful guides to denote the dominance of the radiative recombination in the active region of the device. The minimum ideality factor is proposed as a possible figure of merit for the defect level of the epitaxial layers of the device and shown to be correlated with the maximum IQE value.

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

“…The photocurrent at V oc , i.e., I ph (V oc ), can be smaller than the one under short-circuit condition, I ph (0) � I sc , due to different band alignments. 14 It is assumed that…”

“…It is based on the assumption that the photoluminescence (PL) powers under short-and open-circuit conditions are found to be all proportional to I sc . 14 Combining with eqs 1 and 2, one can rewrite eq 3 as i k j j j j j y…”

Extracting the inherent ideality factor of a diode from electrical current–voltage characteristics

“…Since the ideality factor indicates the dominance of different current conductions or recombination processes, the ideality factor is typically evaluated as a function of current to gain information on the current level at which the desired diffusion current in Si or the radiative recombination current in the LED becomes dominant [1,6]. When measured as a function of current, the ideality factor usually starts at a value equal to or greater than two at very low currents, due to such processes as the SRH recombination or the tunnelling conduction [1,5,6]. As the current is increased further, the ideality factor decreases and approaches a value of one with the diffusion current or the radiative recombination current becoming more dominant in the total current [1,6].…”

“…When measured as a function of current, the ideality factor usually starts at a value equal to or greater than two at very low currents, due to such processes as the SRH recombination or the tunnelling conduction [1,5,6]. As the current is increased further, the ideality factor decreases and approaches a value of one with the diffusion current or the radiative recombination current becoming more dominant in the total current [1,6]. At higher currents, the potential drop outside the junction caused commonly by the series resistance is no longer negligible.…”

“…At higher currents, the potential drop outside the junction caused commonly by the series resistance is no longer negligible. Because of the potential drop outside the junction, the ideality factor evaluated from the current-voltage (I-V) characteristics now increases with current after reaching the minimum [1,6]. This increase in the ideality factor at high current levels does not reflect the inherent ideality factor since the main current conduction mechanism, either diffusion or radiative recombination, is still considered to be dominant at high currents.…”