Study Of Semipolar(11-22)GaN Grown On Silicon Substrate And Its Heterojunction Properties

GaN-based light-emitting diodes(LEDs)have been widely used in lighting and display fields due to their low cost,high luminous efficiency,and long lifetime.The key factor restricting the further improvement of the luminous efficiency of GaN-based LEDs is the quantum confined Stark effect(QCSE).Compared with conventional c-plane GaN-based LEDs,semi-polar GaN-based LEDs can significantly reduce QCSE,but it is currently difficult to grow semi-polar GaN using heteroepitaxial methods.In this paper,the patterned(113)silicon substrate was prepared by photolithography and wet etching,and the(11-22)semipolar GaN material was successfully grown on the patterned(113)silicon substrate using metal organic chemical vapor deposition(MOCVD).In addition,heterojunctions composed of traditional semiconductor material GaN and emerging two-dimensional material MoS₂ are also used in some optoelectronic devices.Semipolar GaN heterojunctions are expected to improve device performance.In this paper,two kinds of MoS₂/GaN heterojunctions were prepared by combining polar and semipolar GaN with MoS₂,respectively,and the band offsets of the two heterojunctions were measured by X-ray photoelectron spectroscopy(XPS).The main research contents are as follows:1.Selecting(113)as the crystal orientation of the silicon substrate,and the patterned silicon substrate is prepared by photolithography and wet etching.After calculation,the angle of the lithography stripe to the reference plane of the silicon wafer should be 73.2°.The etchant without IPA has better effect.Increasing the temperature and prolonging the time will increase the corrosion depth of the silicon wafer.The silicon wafer etching conditions selected in this paper are as followed:35wt%KOH solution as the etchant,the etching time is 20min,and the etching temperature is 40?.2.Two methods have been used in the epitaxial growth of semipolar(11-22)GaN on patterned(113)silicon substrates by MOCVD,namely,the direct growth method and the high temperature-low temperature GaN layers growth method.The GaN grown by the latter growth method has a better effect.There are two schemes to grow semipolar(11-22)GaN.For Scheme 1,first,grow the Al N buffer layer at 1120°C for10min with a V/III ratio of 700.Then,the GaN buffer layer with a V/III ratio of 700was grown for 60 minutes at 1100°C.Finally,a low-temperature GaN layer with a V/III ratio of 700 was grown for 90 minutes at 1040°C.Scheme 2 is based on Scheme 1,and the V/III ratios of both the high-temperature GaN layer and the low-temperature GaN layer are changed from 700 to 1500.A series of characterizations were subsequently performed on the semipolar GaN of these two schemes.3.MoS₂/(11-22)GaN and MoS₂/(0001)GaN heterojunctions were fabricated,and the heterojunctions were characterized by Raman spectroscopy and X-ray diffraction(XRD).The band alignment of the MoS₂/(11-22)GaN and MoS₂/(0001)GaN heterojunctions are determined by X-ray photoelectron spectroscopy(XPS).The measurement result of the valence band offsets of the two MoS₂/GaN heterojunctions is 1.54±0.15 e V.And the conduction band offsets are determined to be 0.29±0.15 e V,revealing type-II band alignments of the two heterojunctions.