A Study Of AlN/GaN Digital Alloy Barrier Quasi-AlGaN/GaN Heterostructure

AlGaN/GaN HEMT is promising for the application to high frequency and high power devices, high voltage devices and high temperature devices because of their wide bandgap, strong polarization, high electron density, high electron mobility and high breakdown field strength. In order to improve the HEMT device performance, low sheet resistance is needed. An AlGaN barrier with high Al fraction is one solution for this. However, with the increase of the Al composition, the quality of the AlGaN barrier becomes exacerbated, sheet resistance will increases when the Al content exceeds a certain level. One approach to solve this issue is to use the AlN/GaN digital alloys as AlGaN barrier. Based on this, the main results of this paper are as follows:1. The influences of metal organics on the properties of AN/GaN digital alloys barrier heterostructure were studied. When the flow of metal organics decreases, the growth rate of GaN and AN in barrier will decrease. The growth rate of GaN decreases more. Al composition of barrier increases and the surface morphology of the heterostructure will deteriorate.2. The influences of barrier growth temperature on the properties of AlN/GaN digital alloys barrier heterostructure were studied. When the temperature increases, the growth rate of GaN and AlN in barrier will decrease. The growth rate of GaN decreases more. The decomposition rate of GaN is very small and nearly independent on temperature. The decomposition rate of AN decreases with tempetature increasing. Al composition of barrier increases and barrier thickness decreases. The surface morphology of the heterostructure will get improved with growth rate decreasing. When growth rate is very small, the growth model will turn from digital alloy growth to compound growth and the surface morphology of the heterostructure will deteriorate.3. The influences of the GaN cap layer and AN insert layer on the properties of heterostructure were studied. By inserting GaN cap layer and AN insert layer, the 2DEG sheet density and mobility of the heterostructure increase, and the sheet resistance of the heterostructure decreases. The surface morphology of the sample can get improved.4. The comparation of AIN/GaN digital alloys barrier heterostructure and traditional AlGaN barrier heterostructure were studied. The 2DEG sheet density,2DEG mobility and sheet resistance of the digital alloys barrier heterostructure are close to those of traditional AlGaN barrier heterostructure. The surface morphology of the digital alloys barrier heterostructure is better with clear atom steps and less surface pits.