Research On Laser Lift-off Of GaN LED Thin Films

GaN is a very favorable materials system for short-wavelength optical device. The band gap of GaN-based material can be tuned between 1.9 eV and 6.2 eV, ranging from red to ultraviolet(UV).The GaN-based systems have promising applications in the optoelectronic industry,in particular blue/UV light LEDs,laser diodes(LD),UV detectors.A combination of wafer bonding and thin-film lift-off offers the greatest flexibility of joining dissimilar materials and provides a new research for growth and device fabrication.In this article successful separation of GaN from GaN/sapphire structures was accomplished by laser lift-off,and the reutilization of sapphire substrate was realized.We also optimize the parameters of lift-off process,and lower the threshold energy density to quick laser lift off process.There are not such reports at home and abroad yet.Main works include:(1)A thin GaN LED films,grown on 2 inch diameter sapphire substrates,was separated by laser lift-off.The transferred GaN thin film is smooth and intact.It remains the InGaN/GaN MQW's structural and it is rougher compared the one before the lift-off process.It is due to thermodynamic decomposition of GaN film in the lift-off process and high lattice mismatch between the GaN and sapphire(2)lnGaN/ GaN multi-quantum-wells(MQW's) structure was grown on the separated sapphire substrate later and compared with that of grown on the conventional substrate in the same condition.PL spectrum and Raman spectrum indict that PL peak blueshift due to the relaxation of GaN LED films after sapphire polishing process.By the comparison of XRD spectrum,the mechanical polishing process takes bad effect to the GaN films quality.In order to improve the quality of crystal quality,further study about polishing technique of sapphire substrate must be carried out.(3)By analyzing the relationship between the pressure and decompose temperature of GaN,a novel method was presented to lower energy density and aim fast processing.(4)We achieve fast processing of laser lift-off by heating the substrate which can lower threshold density and magnify the facula.