结温对高压白光LED光谱特性的影响

Effect of Junction Temperature on EL Spectra of GaN-Based White High Voltage LEDs

高压LED因其自身突出的特点在照明领域有着潜在的应用优势,但作为一种新型功率LED,其光电热特性仍需深入研究。该实验对6和9V GaN基高压LED芯片进行了相同结构和工艺条件的封装,对封装样品进行了10~70℃的变温度光谱测试,并进行了从控温平台温度到器件结温的转换。为保证器件的电流密度相同,6和9V样品光谱测试的工作电流分别设定为150和100mA。结果显示,结温升高会导致蓝光峰值波长红移、波长半高宽增大、光效下降和显色指数上升等现象。在相同平台温度和注入功率下,9V样品的结温低于6V样品;随着温度的升高,9V样品波长半高宽的增加量比6V样品少1.3nm,光效下降量少1.13lm·W^(-1),显色指数上升量少0.28。以上表明,与低压LED相比,高压LED有着更低的工作结温和更小的温度影响。原因在于,相同环境温度下高压LED具有更好的电流扩展性和更少的发热量。此特性在高压LED的研究、发展与应用等方面具有参考价值。此外,峰值波长仍与结温有着较好的线性度,在光谱设备精度较高的情况下可继续作为结温的敏感参数。

High voltage light emitting diodes（HV-LEDs）have potential advantages on general lighting application for their special features.But as novel power LEDs,their optical,electrical and thermal characteristics still need to be further studied.In this paper,6and 9V GaN-based HV-LEDs were packaged in the same package structure and process conditions.The optical characteristics of two samples were investigated under different temperatures range from 10 to 70 ℃ which were calibrated to junction temperatures using thermal impedance measurement.To ensure the same current density,working current was set to150 mA for 6V sample and 100 mA for 9Vsample respectively.Results show that the increasing junction temperature has a great effect on EL spectra of two samples,such as peak wavelength red-shifting,full width at half maximum（FWHM）broadening,luminous efficiency reducing and color rendering index（CRI）increasing.The junction temperature of 9Vsample is lower than that of 6V sample in the same platform temperature and injection power.With temperature increasing,the extended quantitative value of FWHM for 9Vsample is 1.3nm less than that of 6V sample,the reduced quantitative value of luminous efficiency is 1.13lm·W-1 less than that of 6V sample,while the increased quantitative value of CRI is 0.28 less than that of 6V sample.Those data suggest that EL spectra of HV-LEDs is less affected by junction temperature than traditional LEDs.It is because HV-LEDs perform better in current spreading and generate less heat.This conclusion has reference value for study,development and applications of GaN-based HV-LEDs.In addition,peak wavelength still has a good linear relationship with junction temperature and it can be a temperature-sensitive parameter when the spectra measurement accuracy is enough.