Influence Of Thermal Shock On InGaN/GaN MQW Blue LEDs On Si Substrate

As the most promising optoelectronic material, the light emitting diode(LED) has attracted great interests in several applications including solid state lighting and information display, etc. because of its enormous economic and social significance. It is particularly important for our country to have LED characterized of energy saving, low-maintenance, long life and high reliability. In spite of the rapid and astonishing development, commercially available LEDs still have many problem remained that hinder further progress. One of the most difficulties lies in the differences of lattice constant and thermal expansion among LED chip layers.In the case of LED, the component level's reliability test and failure analysis are achieved by LED makers. ESD, high humidity, high temperature and high current bias and so on can be the examples. However, the influence of thermal shock which impacts thermal expansion prominently is still an ambiguity.In this thesis, we have had a study on injection current and ambient temperature impact on the device performance. Especially, we have investigated the influence of thermal shock and high temperature bias on InGaN/GaN MQW blue LEDs and correlative failure mechanism. The contents of the study and the significant results are followed as:1. Injection current and ambient temperature dependence of electroluminescence(EL) spectral and forward I-V curves of InGaN/GaN MQW blue LEDs on Si substrate have been studied over a wide temperature range(T-100～350K) and as a function of injection current level(0.05～200mA). It was found that, our LED chips had good performance dependence of injection current and ambient temperature. Moreover, the current density of EQE peak increased exponentially with the ambient temperature rising.2. Influence of thermal shock and high temperature bias on blue LEDs on Si substrate was first investigated. It was found, forward voltage and series resistance rose as the injection current increasing, while the influence of thermal shock was more obvious. Moreover, thermal shock and high temperature bias impacted the wavelength of the devices slightly and the luminous intensity remarkably. And their luminous intensity all showed decrease after thermal shock and high temperature bias. Whatmore, the influence of high temperature bias on the luminous intensity was more visible. However, the EL peak had no clear influence with forward current increasing.3. Chips with Ag reflection layer sufferred from huge thermal degradation when shock temperature rose to 573K, which reduced the EL intensity awfully and darkened the chip surface. Contrasted the optical and electrical properties of chips with and without Ag mirrors, the agglomeration of Ag reflector layer was considered as the main reason for the significant reduction of the sample's EL intensity.This paper is supported by Program for Changjiang Scholars and Innovative Research Team in University(IRT0730) and National High Technology Research Development Program(2006 AA03 A128).