Study On The Growth Of GaN Films And The Property Improvement Of GaN LED On Silicon Substrate

Solid State lighting lamps with GaN based LED chips are considered as thepreferred candidates for the next generation lighting, due to their high efficiency,long lifetime, fast modulation speed, good robustness to shocks and atmosphericagents, near linear behavior under continuous current and pulsed width, and free ofmercury. As the research and industrialization carry forward, the material growthand device manufacture technology has made great advancements over the years.Chip efficiency and reliability has also been greatly improved. Especially, thesuccessful growth of GaN and fabrication of high efficiency LED chips on siliconsubstrates has further cut the device cost, which speeds up the replacement ofincandescent lamps and fluorescent lamps as the generation lamps.Under this background, this dissertation focuses on the growth of GaN materialand LED device on silicon substrates. Firstly, lateral epitaxial overgrowth of GaNsubstrate was investigated on patterned Si (111) substrates with annealed Al-Si alloyfilm as mask and the epitaxial growth of GaN LED structure was studied on Si (111)substrates with different resistivity. Secondly, same temperature cap layer wasinduced after quantum well in green LED. The effect of cap layer thickness on thequality of QW InGaN materials and photoluminescence spectra of InGaN/GaNLEDs was researched. The efficiency improvement of blue GaN LED was alsostudied by n-GaN surface roughening with40%NaOH solution at80℃for10minutes. Lastly, the reliability of high-power vertical GaN LEDs on silicon wasstudied.The following innovative and meaningful research results were conluded：1、 Al-Si alloy mask was formed by evaporating150Al metal film on silicon(111)substrate, Al film patterning and annealing at1200℃. The results show thanAlN and GaN can’t be nucleated on Al-Si alloy mask. So, Al-Si alloytechnology is an effective mask for GaN selective-area growth on siliconsubstrates. 2、 Epitaxial lateral growth GaN was studied on patterned Si (111) substrate with5μm period square Al-Si alloy layer as mask. When the square area is siliconsurface, only pyramid-shaped selective-area growth GaN crystal can be formedwith six GaN {1-100} planes exposed. When square area is covered by Al-Sialloy mask, GaN reticular films covered the silicon film and mask square can’tbe fully covered with forming a reversed pyramid voids on it3、 Epitaxial lateral growth GaN was studied on patterned Si (111) substrate with4μm period stripy Al-Si alloy layer as mask. When the mask stripes are parallelto GaN [11-20] directon, only Independent triangle GaN stripes can be grownon the Si substrate. When the mask stripe are Parallel to GaN[1-100] direction,the lateral epitaxy overgrowth was improved and crack-free GaN crystalcontinuous films were successfully grown on the Al-Si alloy masked Si (111)substrate by increasing growth temperature and decreasing growth pressure.4、 Same temperature (ST) GaN cap layer after QW was induced in InGaN/GaNMQWs green LED. Relative thicker cap layer is benefit to promote Incomponent, homogeneity of InGaN well, and the interaface abruptnessof theMQWs. The n-GaN roughened vertical green LED with25cap layer haslarger quantum conversion efficiency. Under35A/cm2direct current（DC）driven, the1140um1140μm silica pakeaged LED has28.1%EQE,235mWoutput power,519nm domain wavelength and2.99V operating voltage.5、 P-GaN layer under500Torr pressure was induced in the LED epitaxial layerhaving big V-pits in InGaN/GaN MQWs. The results show that thehigh-pressure P-GaN layer could effectively landfill the V-pits, reduce reverselakage current and improve lighting efficiency. Under35A/cm2DC driven, the11400um1140μm vertical blue LED chip with high-pressure layer has79.5%IQE. The silica pakeaged LED has595mW output power,450nm domainwavelength and3.05V operating voltage.