Efficiency Improvement for III-V Nitride Micro Light-Emitting Diodes
MetadataShow full item record
As a solid-state lighting source with high luminance and long life-time, the gallium nitride/ indium gallium nitride (GaN/InGaN) light-emitting diode (LED) is considered as a promising technology for many applications, including opto-genetic neuromodulation, micro-indicators and self-emissive micro-displays. The biggest technical challenge with conventional GaN/InGaN LEDs is the so-called efficiency droop, which is mainly attributed to three reasons: Auger recombination, low hole injection and carrier overflow. On the contrary, the substantial carrier loss due to Shockley–Read–Hall (SRH) surface recombination is usually ignored in conventional GaN/InGaN LEDs. However, when the size of the GaN/InGaN LEDs shrinks down to a few micrometers, the increased surface area to volume ratio leads to a high carrier surface recombination rate, which significantly degrades the efficiency performance of GaN/InGaN micro-LEDs (μ-LEDs). In this case, the surface recombination velocity (SRV), which reflects the impact of surface recombination rate, becomes the most critical parameter affecting the device performance. This thesis investigates the surface recombination impacts on the efficiency performance of size-dependent GaN/InGaN μ-LEDs. In this work, the simulation tool APSYS crosslight is employed to simulate GaN-based μ-LEDs by setting the SRV to 3×104 cm/s at room temperature. The simulation results show that the internal quantum efficiency of μ-LEDs decreases from 53% to 4% when the size shrinks down from 100μm to 5μm. The simulation results are then confirmed with the temperature-dependent experimental data measured on 50×50 μm2 μ-LEDs. Further investigation shows GaN/InGaN μ-LEDs with n-doped quantum barriers significantly improved the efficiency of LEDs in common working current density range. Based on the modeling results, a new design of GaN/InGaN μ-LEDs with n-doped quantum barriers are proposed to improve the efficiency in GaN/InGaN μ-LEDs with small sizes (<10μm in dimension). For GaN/InGaN μ-LEDs with n-doped quantum barriers, calculation shows that the SRH recombination rate (surface recombination) in the n-GaN is much smaller than the p-GaN. By considering the tradeoff between balance of electron-hole injection and suppressing surface recombination, an optimized 5×5 μm2 GaN/InGaN μ-LEDs with n-doped quantum barriers and single quantum well design is presented. The estimated efficiency of the new design is two times higher than that in conventional intrinsic multiple quantum wells based μ-LEDs.
Cite this version of the work
Jian Yin (2019). Efficiency Improvement for III-V Nitride Micro Light-Emitting Diodes. UWSpace. http://hdl.handle.net/10012/15033