Diode junction temperature in ultraviolet AlGaN quantum-disks-in-nanowires

Abstract

The diode junction temperature (Tj) of light emitting devices is a key parameter affecting the efficiency, output power, and reliability. Herein, we present experimental measurements of the Tj on ultraviolet (UV) AlGaN nanowire (NW) light emitting diodes (LEDs), grown on a thin metal-film and silicon substrate using the diode forward voltage and electroluminescence peak-shift methods. The forward-voltage vs temperature curves show temperature coefficient dVF/dT values of −6.3 mV/°C and −5.2 mV/°C, respectively. The significantly smaller Tj of ∼61 °C is measured for the sample on the metal substrate, as compared to that of the sample on silicon (∼105 °C), at 50 mA, which results from the better electrical-to-optical energy conversion and the absence of the thermally insulating SiNx at the NWs/silicon interface. In contrast to the reported higher Tj values for AlGaN planar LEDs exhibiting low lateral and vertical heat dissipation, we obtained a relatively lower Tj at similar values of injection current. Lower temperatures are also achieved using an Infrared camera, confirming that the Tj reaches higher values than the overall device temperature. Furthermore, the heat source density is simulated and compared to experimental data. This work provides insight into addressing the high junction temperature limitations in light-emitters, by using a highly conductive thin metal substrate, and it aims to realize UV AlGaN NWs for high power and reliable emitting devices.

Heat Dissipation in Flexible Nitride Nanowire Light-Emitting Diodes

“…Since the EL broadening prevented us from using the emission wavelength as a probe of the junction temperature, infrared imaging was used to monitor the LED heating. We measured the temperature distribution of the device surface by using an infrared camera as described in [28] for injected current increased by steps of 50 mA from 100 to 350 mA. Thermal maps of the LED and the surrounding background had spatial resolution of~150 µm per pixel.…”

“…While the thermal properties of thin-film nitride LEDs were thoroughly studied in the literature [23][24][25][26][27], only a few studies address the thermal behavior of NW LEDs focusing on axial-junction devices [28,29]. To the best of our knowledge, no reports exist on heat dissipation in either radial-junction or flexible nitride NW LEDs.…”

“…Another widely applied method to probe LED temperature is based on measurement of the peak wavelength shift with temperature [32,34]. It is commonly accepted that accuracy of the peak energy value is about 10% of the emission linewidth, yielding precision of ±24 • C for standard LEDs [28,30,32]. However, it is challenging to determine the peak wavelength in NW-based nitride LEDs due to alloy-broadening effects that strongly degrade the accuracy of the method [30], and because current injection lines are prone to changing with bias, which results in a shift of electroluminescence peak that is not related to junction temperature [35,36].…”

A Novel Microtiter Plate Format High Power Open Source LED Array

“…To minimize calibration errors of the IR camera, it was calibrated under the same conditions for all measurements. Using IR images as a method to obtain the surface temperature was chosen, as this was shown to be accurate [26].…”

Functional integrity and stable high-temperature operation of planarized ultraviolet-A AlxGa1−xN/AlyGa1−yN multiple-quantum-disk nanowire LEDs with charge-conduction promoting interlayer

“…Such applications require highly stable UV devices suitable for use in high-temperature and otherwise harsh environments. 13,16,17 We have previously grown and fabricated UV-A quantum-confined Al x Ga 1−x N/Al y Ga 1−y N nanowire-based light-emitting diodes (LEDs) and examined their steady-state electro-and photoluminescent characteristics at room temperature. 18,19 Here, we expand the scope of that work by investigating the operational stability of the device across a wide range of operation temperatures (T ), namely −50-100 • C, electromechanically supported by a conformal parylene-C planarization layer, forming a nanowire forest as a polymer/nanowire three-dimensional (3D) composite material.…”