Preparation And Investigation Of AlGaN-Based Polarization-induced Tunneling Junction On SiC Substrate

AlGaN-based tunneling junction diodes can be used in an ultraviolet light emitting diode?LED?to implement p-n inversion structure to improve carrier injection efficiency.Since the AlGaN-based tunneling junction diodes have a wide band gap,a reasonable structural design can achieve a high transmittance for the UV LED active region,which is advantageous for improving the light extraction efficiency of the UV LED.In addition,the UV LED structure with tunneling junction can avoid the preparation of p-type electrodes,effectively solving the problem that ohmic contact of p-type AlGaN materials is difficult to achieve.However,due to the higher donor and acceptor activation of AlGaN materials,it is difficult to achieve higher concentration doping,resulting in poor electrical conductivity of AlGaN-based tunneling junctions,which greatly limits the application of AlGaN-based tunneling junction diodes.In order to solve the problems in the AlGaN-based tunneling junction,this paper proposes to use the inherent polarization characteristics of the AlGaN-based material to improve the electron concentration on the n-type side and the hole concentration on the p-type side of the tunneling junction,that is,AlGaN,which is linearly changed by the Al composition,is used as the polarization-inducing doping layer to increase the carrier concentration of n-type materials and p-type materials,in addition,an AlGaN layer with a high Al composition is interposed between the n-type AlGaN layer and the p-type AlGaN layer for realizing a high concentration of two-dimensional electron gas and hole gas at the interface,thereby further improving the tunneling probability of the device,and obtaining a tunneling junction device with good performance.In this paper,we used metal organic chemical vapor deposition?MOCVD?technology to carry out experimental research.The specific research work was as follows:1.Polarization-induced n-type AlGaN materials were prepared by MOCVD method.We studied the effects that the structure of Al?Ga?N buffer layer,the V/III ratio of AlN buffer layer,the growth temperature of u-Al_0.3Ga_0.7N template layer,and the doping and thickness of n-type polarization induced doping layer on the surface morphology,resistivity and electron concentration of the polarization-induced n-type AlGaN material.Through optimization,we obtained an n-type AlGaN material with high crystal quality and good electrical properties,and its electron concentration is 1.8×10¹⁸ cm^-3 and the resistivity is 0.01?·cm.2.Polarization-induced p-type AlGaN materials were prepared by MOCVD method.We studied the effects that the V/III ratio of AlN buffer layer,the V/III ratio of the u-Al_0.6Ga_0.4N template layer,the annealing temperature and the thickness of p-type polarization induced doping layer on the resistivity and hole concentration of polarization-induced p-type AlGaN material.Through optimization,we obtained a p-type AlGaN material with high crystal quality and good electrical properties,and its electron concentration is 3.9×10¹⁷ cm^-3 and the resistivity is 5.33?·cm.3.Based on the polarization induction and tunneling principles,the study of AlGaN-based polarization-induced tunneling junctions on SiC substrates was carried out.The effects that the structure of the p-type layer,the thickness of the AlGaN polarization-inducing intercalation layer and the composition of the AlGaN polarization-inducing intercalation layer on the structural and electrical properties of the polarization-induced tunneling junction were investigated,and through the optimization,a tunneling junction structure with excellent performance was prepared,which has a large reverse current density,and the current density is 5.5 mA/cm² at a reverse bias voltage of 4.5V.4.LED with polarization-induced tunneling junction was further fabricated on SiC substrate,and its structural,optical and electrical properties were investigated.An LED structure with an emission wavelength of 330 nm was prepared,and the device exhibited good rectification characteristics,and its turn-on voltage was 5 V,and the leakage current was on the order of ?A.