Comparison of alloy disorder scatterings in Ga- and N-polar AlGaN/GaN heterostructures

The two-dimensional electron gas (2DEG) mobilities limited by alloy disorder (AD) scattering in both Ga- and N-polar AlGaN/GaN heterostructures are investigated. It was found that the AD scattering limited electron mobility in N-polar heterostructures is on the order of 10(3)10(4) cm(2)/Vs, which is comparable to the optical phonon scattering at room-temperature. In comparison, the AD scattering in Ga-polar samples is much less important. Moreover, the electron mobility decreases with the 2DEG density in the Ga-polar device but shows a reverse trend in the N-polar counterpart. This is found to be caused by the rather different electric field distributions in Ga- and N-polar AlGaN/GaN heterostructures. In addition, we find that an AlN interlayer can effectively reduce the alloy scattering, mainly due to the large band offset between AlN and GaN. The calculated mobilities have been compared with the experiment results and good agreements are found. We believe that our results are important for the design of AlGaN/GaN heterostructure-based devices, especially the N-polar ones.