Abstract
Junction temperature (Tj) and current have important effects on light-emitting diode (LED) properties. Therefore, the electroluminescence (EL) spectra of blue and green LEDs were investigated in a Tj range of 120–373 K and in a current range of 80–240 mA based on accurate real-time measurements of Tj using an LED with a built-in sensor unit. Two maxima of the emission peak energy with changing Tj were observed for the green LED, while the blue LED showed one maximum. This was explained by the transition between the donor-bound excitons (DX) and free excitons A (FXA) in the green LED. At low temperatures, the emission peak energy, full width at half maximum (FWHM), and radiation power of the green LED increase rapidly with increasing current, while those of the blue LED increase slightly. This is because when the strong spatial potential fluctuation and low exciton mobility in the green LED is exhibited, with the current increasing, more bonded excitons are found in different potential valleys. With a shallower potential valley and higher exciton mobility, excitons are mostly bound around the potential minima. The higher threshold voltage of the LEDs at low temperatures may be due to the combined effects of the band gap, dynamic resistance, piezoelectric polarization, and electron-blocking layer (EBL).
Highlights
GaN-based light-emitting diodes (LEDs) have been widely used for industrial lighting and outstanding backlight in liquid crystal displays and have become an increasingly important technology [1,2,3]
To fabricate a LED module with better color quality or better color coordinates, or with application in extreme temperature range, it is necessary to understand the electroluminescence mechanism in LEDs under wide range of the Tj and the injection current
We investigated the mechanisms of the LED peak energy changes, changes, and in particular thethe effect of thecurrent injection andemission
Summary
GaN-based light-emitting diodes (LEDs) have been widely used for industrial lighting and outstanding backlight in liquid crystal displays and have become an increasingly important technology [1,2,3]. Tunable white-light engines (changing color temperature), high-quality display, and tunable color lighting (changing color) have attracted intense interest [4]. Changing the current will lead to a change in the junction temperature (Tj ) and emission peak wavelength [5], and the Tj itself is a key factor influencing the LED emission peak [6]. For some use in manufacturing applications, LED lighting must be able to function in extreme ambient conditions, such as a high-temperature environment (furnace lighting) and freezing environment (hyperborean lighting). To fabricate a LED module with better color quality or better color coordinates, or with application in extreme temperature range, it is necessary to understand the electroluminescence mechanism in LEDs under wide range of the Tj and the injection current
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