Mechanism Analysis of Proton Irradiation-Induced Increase of 3-dB Bandwidth of GaN-Based Microlight-Emitting Diodes for Space Light Communication

Abstract

Influences of 170-keV protons beam irradiation on the static and dynamic properties of blue light InGaN/GaN multiple quantum wells (MQWs) microlight-emitting diodes (Micro-LEDs) were investigated. It was interesting to find out that, although threshold voltage and light output power of Micro-LEDs deteriorated after proton irradiation, a 3-dB bandwidth was greatly improved. In quantitative terms, at the forward current density of 1 kA/cm2, 3-dB bandwidth increased from original 7.34 to 119.74 MHz when Micro-LED exposed to proton beam with the fluence of $5\times 10^{14}$ p/cm2. Based on the frequency response data analysis, differential carrier lifetimes of Micro-LEDs, including Shockley–Read–Hall (SRH) lifetime and differential radiation recombination lifetime, were compared. The results pointed out that both SRH and recombination lifetimes became shorter after proton irradiation, indicating that competition between the nonradiative and radiative recombination processes was enhanced by proton beam. To reveal the origination of the 3-dB bandwidth improvement, photoluminescence (PL) and time-resolved PL (TRPL) spectrums of Micro-LEDs were measured. MQWs’ PL spectrum with a peak wavelength of 450 nm was observed and its intensity decreased as proton fluence increasing. Meanwhile, a PL peak at 550 nm, which was well known as defect-related PL spectrum, was enhanced by proton irradiation, especially at a proton fluence of $5\times 10^{13}$ and $5\times 10^{14}$ p/cm2, proving the increase of defects in epitaxial thin films as proton fluence increasing. In the TRPL experimental study, the nonradiative recombination lifetime decreased with proton fluence, which was consistent with the results analyzed by frequency response. Overall, the improvement of 3-dB bandwidth could be mainly attributed to the decrease of carrier lifetime in MQWs, which were caused by the generation of defects due to the atom displacement effect of proton irradiation.