Abstract:We investigate the influence of carrier overflow on the forward-voltage characteristics of the InGaN-based blue light-emitting-diode (LED) by comparing the temperature-dependent characteristics of the electroluminescence (EL) efficiency, the EL spectra, and the current-voltage relation over a wide range of temperature (50–300 K). Based on these experimental results, we demonstrate that the simple ohmic potential drop in the Shockley diode equation is not sufficient to explain the experimental data when the sev… Show more
“…The decrease in applied voltage with elevated temperature in the entire current region, particularly the change in slope in the logarithmic curve at a low current regime (10 –6 A–10 –4 A) (Fig. 1 d), suggests not only the change in bandgap energy but also the change in predominant carrier conduction and recombination mechanisms since it represents an ideality factor of LED device 3 , 29 , which is discussed in detail later in this section. Figure 1 The light output powers (LOPs) and applied voltages ( V ) of the sample under investigation as functions of driving current at various operating temperatures: ( a , b ) on linear scales; ( c , d ) on logarithmic scales.…”
Section: Experimental Results Analysis and Discussionmentioning
confidence: 91%
“…The decrease in applied voltage with elevated temperature in the entire current region, particularly the change in slope in the logarithmic curve at a low current regime (10 -6 A-10 -4 A) ( Fig. 1d), suggests not only the change in bandgap energy but also the change in predominant carrier conduction and recombination mechanisms since it represents an ideality factor of LED device 3,29 , which is discussed in detail later in this section.…”
Section: Experimental Results Analysis and Discussionmentioning
confidence: 93%
“…6a. The driving-current-dependent characteristics of B seems to be typical: the QCSE associated with the screening effect is predominant in the low-current regime (below the current at the IQE peak) and the PSF is predominant in the high-current regime (above the current at the IQE peak) 29,31 . Notably, B gradually decreases with elevated temperature over the entire current range, implying a gradual reduction of the radiative recombination probability as the operating temperature is increased.…”
Section: Experimental Results Analysis and Discussionmentioning
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.
“…The decrease in applied voltage with elevated temperature in the entire current region, particularly the change in slope in the logarithmic curve at a low current regime (10 –6 A–10 –4 A) (Fig. 1 d), suggests not only the change in bandgap energy but also the change in predominant carrier conduction and recombination mechanisms since it represents an ideality factor of LED device 3 , 29 , which is discussed in detail later in this section. Figure 1 The light output powers (LOPs) and applied voltages ( V ) of the sample under investigation as functions of driving current at various operating temperatures: ( a , b ) on linear scales; ( c , d ) on logarithmic scales.…”
Section: Experimental Results Analysis and Discussionmentioning
confidence: 91%
“…The decrease in applied voltage with elevated temperature in the entire current region, particularly the change in slope in the logarithmic curve at a low current regime (10 -6 A-10 -4 A) ( Fig. 1d), suggests not only the change in bandgap energy but also the change in predominant carrier conduction and recombination mechanisms since it represents an ideality factor of LED device 3,29 , which is discussed in detail later in this section.…”
Section: Experimental Results Analysis and Discussionmentioning
confidence: 93%
“…6a. The driving-current-dependent characteristics of B seems to be typical: the QCSE associated with the screening effect is predominant in the low-current regime (below the current at the IQE peak) and the PSF is predominant in the high-current regime (above the current at the IQE peak) 29,31 . Notably, B gradually decreases with elevated temperature over the entire current range, implying a gradual reduction of the radiative recombination probability as the operating temperature is increased.…”
Section: Experimental Results Analysis and Discussionmentioning
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.
“…In addition to the above-mentioned factors, electron overflow also exists in these devices. The electron overflow not only decreases the EQE and forward-voltage characteristics [18,19], but also results in a sub-band parasitic peak [20,21]. Therefore, the suppression of electron overflow is absolutely favorable for the optical property of the devices.…”
The influence of quantum-well (QW) number on electroluminescence properties was investigated and compared with that of AlN electron blocking layer (EBL) for deep ultraviolet light-emitting diodes (DUV-LEDs). By increasing the QW number, the band emission around 265 nm increased and the parasitic peak around 304 nm was suppressed. From the theoretical calculation, the electron current overflowing to the p-type layer was decreased as the QW number increased under the same injection. Correspondingly, the light output power also increased. The increment of output power from 5 QWs to 10 QWs was less than that from 10 QWs to 40 QWs, which was very different from what has been reported for blue and near-UV LEDs. The parasitic peak was still observed even when the QW number increased to 40. However, it can be suppressed efficiently by 1 nm AlN EBL for LEDs with 5 QWs. The simulation showed that the insertion of a thin EBL increased the barrier height for electron overflow and the electron current in p-type layers decreased significantly. The results contributed to the understanding of behavior of electron overflow in DUV-LEDs.
Efficiency droop in GaN-based light emitting diodes (LEDs) under high injection current density perplexes the development of high-power solid-state lighting. Although the relevant study has lasted for about 10 years, its mechanism is still not thoroughly clear, and consequently its solution is also unsatisfactory up to now. Some emerging applications, e.g., high-speed visible light communication, requiring LED working under extremely high current density, makes the influence of efficiency droop become more serious. This paper reviews the experimental measurements on LED to explain the origins of droop in recent years, especially some new results reported after 2013. Particularly, the carrier lifetime of LED is analyzed intensively and its effects on LED droop behaviors are uncovered. Finally, possible solutions to overcome LED droop are discussed.
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