Growth,Characterization,and Application of High Al-content AIGaN and High Power Ill-Nitride Ultraviolet Emitters

摘要

A study of Si-doped and Mg-doped Al_xGa_(1-x)N up to x approx 50 % and the characteristics of ultraviolet (UV) light emitting diodes (LEDs) with emission wavelengths at 340 nm and 290 nm are reported.By using grading super-lattices (SLs) before n-type AIGaN growth,surface roughness is much improved.Resistivity of 2.9x10~(-2) OMEGAcm and free electron concentrations of 2.9xl0~(18)cm~(-3) are achieved for n-type Al_(0.45)Ga_(0.55)N.The viability of effective p-type doping is defined by a minimum concentration of Mg required to offset the background impurities and,more importantly,a maximum limit above which inversion domains and structural defects start to nucleate,accompanied by a rapid degradation of electrical transport.Resistivity of 10 OMEGAcm and free hole concentrations above 10~(17)cm~(-3) are achieved for Al_xGa_(1-x)N up to x approx 50 % within an optimum window of Mg incorporation.Output powers up to 1.5 mW from small area 340 nm LEDs (< 100 urn diameter) and 110 muW from 290 nm LEDs (100 urn diameter) directly off a planar chip have been achieved under DC condition.For large area encapsulated lamp (1x1 mm~2 device area and 0.52 mm~2 mesa area),output power of 79 mW from 340 nm LEDs and 8.5 mW from 290 nm LEDs are achieved under pulse mode (1kHz,2% duty factor).