Identifying the cause of thermal droop in GaInN-based LEDs by carrier- and thermo-dynamics analysis

Abstract

This study aims to elucidate the carrier dynamics behind thermal droop in GaInN-based blue light-emitting diodes (LEDs) by separating multiple physical factors. To this end, first, we study the differential carrier lifetimes (DCLs) by measuring the impedance of a sample LED under given driving-current conditions over a very wide operating temperature range of 300 K–500 K. The measured DCLs are decoupled into radiative carrier lifetime (τR) and nonradiative carrier lifetime (τNR), via utilization of the experimental DCL data, and then very carefully investigated as a function of driving current over a wide range of operating temperatures. Next, to understand the measurement results of temperature-dependent τR and τNR characteristics, thermodynamic analysis is conducted, which enables to look deeply into the temperature-dependent behavior of the carriers. On the basis of the results, we reveal that thermal droop is originated by the complex dynamics of multiple closely interrelated physical factors instead of a single physical factor. In particular, we discuss the inherent cause of accelerated thermal droop with elevated temperature.

Efficiency Models for GaN-Based Light-Emitting Diodes: Status and Challenges

“…In fact, the QW carrier density is known to be non-uniform across a multi-quantum well active region and may even vary inside each QW due to current crowding and/or QW non-uniformities. Various groups proposed modified ABC models, e.g., to account for a reduced active volume [ 40 ], inhomogeneous carrier distribution [ 41 ], electron leakage [33,42 ], photon quenching [ 43 ], multi-level defects [44], trap-assisted Auger recombination [45], built-in fields [46], or temperature effects [42,47,48]. In any case, ABC models serve as an important bridge between experiment and theory [49].…”

A Critical Review on the Junction Temperature Measurement of Light Emitting Diodes

“…Linear deviations in high pulse values can be attributed to junction heating that leads to calibration of the V f to a higher T j . At high temperatures, thermal droops also increase in the LEDs, which, indeed, intensify the self-heating of the LED [ 191 , 192 , 193 , 194 ]. At low temperatures, deviation from the constant voltage coefficient of temperature can be explained by internal series resistance [ 184 ].…”

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

“…(b) The IQE droop in the high-current regime of the blue sample is not only due to the pure Auger recombination but also the complex mechanisms involved, e.g. the drift-induced carrier escape [20], piezoelectric field-assisted overflow/spill-over [27], hot carrier overshoot [28], and/or defect-assisted Auger recombination [29]. This is inferred as the discrepancy arises from the fact that the CIE decreases as the driving current increases (i.e.…”