Study On Electrical And Thermal Reliability Of Lattice-matched InAlN/GaN HEMTs

Compared with the traditional narrow band gap semiconductor of silicon(Si),the wide band gap gallium nitride(GaN)material has excellent physical properties,such as large breakdown electric field,high electron mobility and electron saturation speed,and high thermal conductivity,which is very suitable for preparing the electronic devices operating at high voltage,high frequency and high temperature.The typical devices are the high electron mobility transistors(HEMTs)based on AlGaN/GaN or InAlN/GaN heterojunction.The barrier layer of traditional AlGaN/GaN HEMTs suffers from strong(inverse)piezoelectric effect,which is easy to cause device performance degradation especially under long-term working conditions.This situation can be effectively avoided by using lattice-matched In0.17Al0.83N/GaN HEMTs.However,some electrical and thermal reliability problems still restrict the further development and commercial application of the devices.It is very important and essential to study these reliability problems,which can directly promote the development of nitride-based electronic devices.In this thesis,several important electrical and thermal reliability problems of In0.17Al0.83N/GaN HEMTs are studied,including long-time high field stress degradation,high temperature environment degradation,premature current breakdown behavior and channel temperature testing.The specific research contents are as follows:1.The high field and high temperature degradation of In0.17Al0.83N/GaN HEMTs are studied.In long-term constant high-field stress tests,degradation of electrical characteristics such as the decrease of output current,the increase of on resistance,the positive drift of threshold voltage and the decrease of transconductance value are observed,which is attributed to the hot carrier effect of the device.In the high temperature experiment,the influence of temperature on the output and transfer characteristics of the device are analyzed.It is found that the output current and transconductance decrease with the increase of temperature,which is related to the decrease of the mobility of the device.At the same time,the concentration of two dimensional electron gas(2DEG)in the channel decreases under the effect of temperature,which leads to the positive movement of threshold voltage.2.The breakdown mechanism of gate current of In0.17Al0.83N/GaN HEMTs is analyzed.The gate bias step stress is applied to the device to monitor the current changes of the source,drain and gate.At the same time,the spatial distribution and evolution of the "hot spot" of the leakage current are observed by the emission microscope,and the specific breakdown path of the device is determined by the optical beam induced resistance change Finally,combined with the simulated electric field distribution of sentaurus,it is proved that the over excited Fowler-Nordheim tunneling current is the main factor of current breakdown,and the conductive dislocation model is used to explain the premature occurrence of current breakdown.3.A new method for evaluating the channel temperature of In0.17Al0.83N/GaN HEMTs is proposed.Based on the results of traditional direct current electrical method and micro Raman spectroscopy,a new electrical method for measuring the channel temperature of GaN based HEMTs is proposed.The triangle distribution of the channel temperature of the device is obtained by the emission microscope,and the result is similar to that of the micro Raman spectroscopy.By evaluating the advantages and disadvantages of different methods,it is confirmed that the new method of emission electrical method proposed in this paper is more suitable for practical large-scale production applications.