Low-Frequency Noise Characterization In AlGaN/GaN HEMT

AlGaN/GaN HEMT device has a high breakdown electron field(3.3mv/cm)and high electron mobility(2×10³cm²·V^-1·s^-1),it has a huge application prospect in sensing,radar,automation,communications and other fields.Over the past two decades,the performance of AlGaN/GaN HEMT has improved significantly,and its relevant theories and methods have matured.Nevertheless,some reliability problems like short channel effect,current collapse effect,hot carrier effect and so on have also emerged,which seriously hinder the widespread application of AlGaN/GaN HEMT,especially in satellite communications,aerospace and other fields with high reliability requirements.Compared with traditional testing measures of reliability,low frequency noise as a non-destructive method is more sensitive,faster and cheaper about the defect information.At present,there are few studies on degradation characteristics of AlGaN/GaN HEMT by using low-frequency noise,and even fewer studies on low-frequency noise at low temperature.In the thesis,the DC and low-frequency noise performance of AlGaN/GaN HEMT are studied under different bias voltage,size and structure,and in low temperature,so as to analyze the degradation characteristics of the device and identify the sources of the low-frequency noise.First this paper studies(1)the low frequency noise characteristics of AlGaN/GaN HEMT in different gate bias,the curve of low frequency noise have been processed according to the channel resistance and Hooge model formula.The results show that when the gate bias is close to or slightly larger than the threshold voltage,the channel under the gate is the dominant noise source.When the gate bias is much bigger than the threshold voltage,the ungated region of the device becomes the dominant noise source.(2)Then in this paper,the DC and low-frequency noise characteristics of the device have been tested and analyzed from 3?m to 20?m gate length.It's found that the reduction of the gate length can improve the DC performance of the device,however at the same time,the noise raises largely due to the increase of the resistance.According to the Mc Whorter model after the normalization processing of the noise,when the gate length is small,the device noise mainly comes from the trapping and detrapping of the channel electrons in the semiconductor.When the gate length is large,the mobility fluctuation is the dominant noise source,which is related to the lattice scattering in the semiconductor.(3)Then,the influence of Si N passivation on AlGaN/GaN HEMT is studied according to compared with the non-passivation device,and the results show that passivation can improve the drain current and transconductance of the device,at the same time it also reduces the gate leakage current and low-frequency noise,and significantly improve the noise in ungated region.At the end of the paper it studies the DC and low-frequency noise characteristics of AlGaN/GaN HEMT at 100K?300K,the results show that(1)the reduce of temperature can improve the drain current,transconductance,and the Schottky characteristic at100K?300K.(2)After testing the FATFET and calculating,it is observed that in the range of the temperature the 2DEG mobility is increasing with reducing the temperature.(3)As for low-frequency noise,according to Mc Whorter model after the normalization processing of the low-frequency noise under different temperature,it is found that when the temperature is less than 200K the deviation between the two curve is observed,the noise is mainly caused by the mobility fluctuation,which is associated with the lattice scattering in semiconductor.When the temperature is between 200K and 300K,the curve matches the model well,the dominant noise is the fluctuation of carrier number,and the trap density is large.(4)Finally,the DC and low-frequency noise characteristics of the device are studied by the change of the gate length at low temperature.It is found that the influence of the gate length change at low temperature on the DC characteristics is weakened and the influence on the mobility fluctuation is intensified compared with that at room temperature.And the low-frequency noise has no correlation with the change of the gate length at low temperature.