Effects of donor density and temperature on electron systems in AlGaN/AlN/GaN and AlGaN/GaN structures

It was reported by Shen et al that thetwo-dimensional electron gas (2DEG) in an AlGaN/AlN/GaN structure showed highdensity and improved mobility compared with an AlGaN/GaN structure, but thepotential of the AlGaN/AlN/GaN structure needs further exploration. By theself-consistent solving of one-dimensional Schr"{o}dinger--Poissonequations, theoretical investigation is carried out about the effects ofdonor density (0--1times 10¹⁹cm^-3 and temperature(50--500K) on the electron systems in the AlGaN/AlN/GaN and AlGaN/GaNstructures. It is found that in the former structure, since the effectiveDelta E_c is larger, the efficiency with which the 2DEG absorbs theelectrons originatingfrom donor ionization is higher, the resistance to parallel conduction isstronger, and the deterioration of 2DEG mobility is slower as the donordensity rises. When temperature rises, the three-dimensional properties ofthe whole electron system become prominent for both of the structures, but thestability of 2DEG is higher in the former structure, which is also ascribedto the larger effective Delta E_c. The Capacitance--Voltage(C-V) carrier densityprofiles at different temperatures are measured for two Schottky diodes onthe considered heterostructure samples separately, showing obviouslydifferent 2DEG densities. And the temperature-dependent tendency of theexperimental curves agrees well with our calculations.