Study On The Preparation And Application Of Chromium-based Metal Substrates For GaN-based LED

GaN, as a direct wide band gap semiconductor, has been widely used for lightemitting diodes (LEDs). The GaN-based LEDs with high power and efficiency havebeen demonstrated a large potential for replacing conventional incandescent light andfluorescence source. Today the GaN-based LEDs in market are either on sapphire orSiC substrate. GaN-based LEDs on silicon, developed by our laboratory, have beenalso succecessfully realized for industrialization. However, these substrates have theirlimitations, respectively. As to sapphire, the GaN-based LEDs not only exhibitundesirable photoelectric properties because of its bad heat and electrical conductivitybut also meet many difficulties in preparation of GaN-based LEDs for it's highhardness. SiC is unsuitable to mass production with high price and cost because it ismonopolized by USA. Silicon with high absorptivity limits the GaN-based LEDs'light output in spite of it's good conductivity and low cost. The aim to overcome thedisadvantage of these obove three substrates and improve the optical and electronicproperties has been considered one of the focuses in GaN-based LEDs reseach, thetechnology of Substrate-lifted-off, which is to bond and transfer GaN expitaxial layergrown on substrate such as sapphire, SiC or Si, onto other new substrates, is one ofthe most important methords to solve this problem. At present, the typicaltransferred subtracte is Si or Cu with adopting bonding technology to transfer.With Introduction of my tutor, we explore a fabrication technology of a newtransferred subtracte which is chromium-based metal substrate.Besides its metalproperties, chromium has high reflectivity, sutiable expansion coefficient similar toGaN and ZnO and strong anti-acid and anti-alkali properties. It is because of theseproperties that we researched the fabrication of chromium-based metal and itsapplication in metal subtrates for Gan-based LEDs.The reseach in the dissertation isas followings:1. Preferred orientation Chromium-based metal substrates, with good roughness ofsurface and planeness, have been made by multi-arc ion plating and selectivechemical erosion technology. Effect of nickel on the properties of chromium basedsubstrates was studied.Besides above work, we have fabricated layered Chromiumbased metal substrates with 316L stainless steel and chromium co-plating. EDX, XRD,SEM and microhardness instrument have been introduced to investigate the properties of chromium-based metal substrates.It is found that: Nickle has obvious influence onthe preferred orientation, surface topography and microhardness of chromium-basedmetal substrates.Also,it can been seen that chromium based metal substrates with316L stainless steel and chromium co-plating have excellent properties.2. GaN expitaxial layers, grown on Si substrates, were successfully transferred ontochromium-based metal substrate by using multi-arc ion plating and selective chemicalerosion technology. The result indicates that co-plating of 316L stainless steel andchromium is benlfical to improve surface planeness and reduce surface cracks of GaNexpitaxial wafers on chromium-based metal substrate. Moreover, arc current shouldnot be too large in order to obtain a surface with less cracks.3 we have investigated the properties ofⅠ-Ⅴcurve, optical power saturation,dominant wavelength, lifetime, antielectronicstate charge of GaN LEDs on chromiumbased metal substrate fabricated by our laboratory. And some certain electronic andoptical properties have met standard of commercialization.This work was supported by the Nanometer Project (No.2003AA302160) andoptoelectronics Project(2005AA311010)...