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InGaN films have been widely used as active layers for blue light-emitting diodes (LEDs) and laser diodes (LDs).[1-3] Recently,indium-rich InGaN alloys have attracted much attention because of their potential applications in the fields of green LEDs and LDs,[4] solar cells,[5-8] and photodetectors,[9,10] thanks to their tunable band gap ranging from infrared to ultraviolet.However,the growth of indium-rich InGaN films,commonly on GaN substrates,suffers from serious problems owing to the large lattice mismatch and growth temperature mismatch between InGaN and GaN,which will induce high strain and may result in dislocations,phase separation,and V-pits.[11,12]Meanwhile,the p-type doping of indium-rich InGaN alloys faces a larger challenge because of the low pdoping efficiency and a high n-type background carrier concentration as well as phase separation.[13]In this work,a fully strain-relaxed InGaN buffer layer was induced in order to achieve an indium-rich InGaN p-n junction with a full strain or less strain relaxation.The indium contents in the n-type layer and in the buffer layer are the same,and thus the n-type layer can grow coherently onto buffer.Structural and photoelectric properties of the indium-rich InGaN p n junction are investigated by using x-ray diffraction (XRD),Raman,and photocurrent response measurements,respectively.