Abstract
On the same micro-LED display panel, LED pixels are always operated with high and low biased voltages simultaneously to show different brightness and colors. Thus, it is vitally important to understand the effect of the heat transmission between LEDs under high and low biased voltages. In this work, we design two different LED groups: Group A is two LEDs bonded together for heat transmission and Group B is two LEDs separated from each other. Then, the two LEDs are operated at one fixed and one tuned biased voltage respectively in each group in a vacuum chamber and the efficiency of the two groups is studied both experimentally and numerically. Here, our experimental results demonstrate that Group A exhibits a maximum improvement of 15.36% in optical output power compared with Group B. The underlying reason is that the wall-plug efficiency of the LED with a voltage lower than photon voltage (V < ℏω/q) is surprisingly enhanced by elevated temperature owing to the heat transmission by the LED under a high biased voltage in Group A. Our further study shows that in such a low voltage region the improvement in the efficiency is attributed to the enhanced carrier concentrations with elevated temperature. On the other hand, the LED in Group A under a high biased voltage further raises the overall efficiency by alleviating the thermal droop due to reduced temperature. Device temperature measurement and numerical calculation of radiative recombination under different temperatures further support the superior performance of Group A LEDs. Our research results can act as the research prototype to design the high-efficient LED arrays for better energy recycling and thermal control.
Highlights
Semiconductor optoelectronic materials and devices develop very fast recent decades [1,2,3,4,5,6]
The blue InGaN/GaN MQW light-emitting diodes (LEDs) wafers used in this work were grown on (0001) c-plane pattern sapphire substrates using an AIXTRON close-coupled showerhead metal-organic chemicalvapor deposition (MOCVD) system
Six pairs of InGaN/GaN MQWs were grown with a 3 nm thick quantum well (QW) and a 9 nm thick quantum barrier (QB)
Summary
Semiconductor optoelectronic materials and devices develop very fast recent decades [1,2,3,4,5,6]. Over the past couple of decades, plenty of architectures and solutions have been proposed to address the scientific and technological challenges introduced by the thermal heat, including adding the heat sink, increasing the heat dissipation area, changing n-electrode length, and exploiting the thermoelectric generator [19,20,21,22,23] All these methods seem to be failed when it comes to the devices with small dimensions and thin films, which have no sufficient space for installing external heat dissipation architectures, for example, Ribbon Filament LED Lamp where LEDs are lined up in a filament. The findings in this work reveal the cooling potential of LEDs and can provide guidelines on thermal management in designing the high-efficient LED arrays, especially for the mini- and micro-LEDs applications, and support the possibility of removing the heat sink
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