Effects of the passivation of SiNx with various growth stoichiometry on the high temperature transport properties of the two-dimensional electron gas in AlxGa1−xN/GaN heterostructures

Effects of the passivation of SiNx on the high temperature transport characteristics of the two-dimensional electron gas (2DEG) in unintentionally doped AlxGa1−xN/GaN heterostructures have been investigated by means of high temperature Hall measurements. The 2DEG density increases much after SiNx passivation, and the increment is proportional to the Si content in SiNx layer, indicating that the increment is mainly caused by ionized Si atoms at the SiN/AlxGa1−xN interface with dangling bonds or by Si atoms incorporated into the AlxGa1−xN layer during the SiNx growth, which is approved by strain analysis and X-ray photoemission spectroscopy (XPS). There is lower 2DEG mobility at room temperature in a passivated sample than in an unpassivated one. However, the 2DEG mobility becomes to be higher in a passivated sample than in an unpassivated one when the temperature is above 250 °C, which is suggested to be caused by different subband occupation ratios in the triangular quantum well at the heterointerface before and after passivation.