Analysis And Research Of ESD On Aging Of GaN/Si Blue LEDs

Recently, growth of GaN on Si substrate has made great progress and it isreported that GaN based luminescence devices on Si substrate have been fabricatedby some groups. Yet, study on properties of GaN based light-emitting diodes(LED)on Si substrate is far from profound, in spite of reliability of GaN based blue orwhite LED on sapphire or SiC substrate had been largely investigated by manyresearchers. By far, analysis and study on anti-electrostatic discharge ability as wellas reliability of GaN based LEDs on Si substrate, which are new products, has notbeen reported, yet. In this dissertation, experiment of electrostatic discharge(ESD)and degradation on GaN based LEDs on Si substrate was studied, Some significantand innovative results achieved is as following:1. Variation of characteristic parameters, electroluminescence(EL) and peakwavelength with current on GaN-vertical LEDs on Si substrate were reported. It isfound that the peak wavelength exists a phenomenon of red- shifting at the begin andblue-shifting following with current, which attributes to competition mechanismbetween band-fitting effect and heating effect in InGaN active layer.2. Degradation characteristics of GaN based LEDs on different substrateswere obtained from accelerating aging experiment with high current. Bydegradation-coefficient-fitting and extrapolation, the calculated life-time of GaNbased LEDs on Si substrate fabricated by our laboratory and on Al₂O₃ substrate is1.84×10⁴ and 2304 hours, respectively. It can be seen that GaN based blue LEDs onSi substrate developed by our laboratory have not only longer calculated life-timebut also high reliability and better ohmic contacts properties than GaN based LEDon Al₂O₃ substrate, which shows GaN based LEDs on Si substrate have encouragingpotentiality in application.3. Effects of ESD on lifetime of GaN based LEDs on Si substrate encapsulatedwith BD457-type-chips and on sapphire substrate were investigated. The lifetime ofGaN LEDs on Si template is 22.6, 21.7, 22.2 and 18.3 thousand hours correspondingto 100,500,1000 voltage with and without ESD stroking, respectively. Above outcomes indicate that GaN based LEDs on Si substrate have good anti-ESD withbearing high ESD-stroking ability, although there exists large dismatching of latticeconstant and heat expansion coefficient between GaN epitaxial layer and Si substratewhich may bring out deficiency having yet no obvious influence on the reliability ofGaN based devices.