Impact of strain relaxation of AlGaN barrier layer on the performance of high Al-content AlGaN/GaN HEMT

The effects of strain relaxation of AlGaN barrier layer on the conduction band profile,electron concentration and two-dimensional gas(2DEG)sheet charge density in a high Al-content AlGaN/GaN high electron mobility transistor(HEMT)are calculated by self-consistently solving Poisson’s and Schr?dinger’s equations.The effect of strain re-laxation on dc I-V characteristics of Al_(x)Ga_(1-x)N/GaN HEMT is obtained by developing a nonlinear charge-control model that describes the accurate relation of 2DEG sheet charge density and gate voltage.The model predicts a highest 2DEG sheet charge density of 2.42×10^(13)cm^(-2)and maximum saturation current of 2482.8 mA/mm at a gate bias of 2 V for 0.7μm Al_(0.5)0Ga_(0.50)N/GaN HEMT with strain relaxation r=0 and 1.49×10^(13)cm^(-2)and 1149.7 mA/mm with strain relaxation r=1.The comparison between simulations and physical measurements shows a good agreement.Results show that the effect of strain relaxation must be considered when analyzing the characteristics of high Al-content AlGaN/GaN HEMT theoretically,and the performance of the devices is improved by decreasing the strain relaxation of AlGaN barrier layer.