Influence of a low-temperature GaN cap layer on the electron concentration in AlGaN/GaN heterostructure

The influence of low-temperature passivating GaN cap layers on the electrophysical parameters of a 2D electron gas (2DEG) in heterostructure high-electron mobility transistors has been studied. It has been found that thin GaN layers deposited in situ at 550$^\circ$C do not exhibit polar properties and do not change the carrier concentration in the 2DEG. However, GaN layers deposited at 830$^\circ$C decrease the carrier concentration in the 2DEG, which is in agreement with theoretical calculations. Using the reflected high-energy electron diffraction technique, it has been established that this effect may be associated with different structures and morphologies of GaN layers deposited at different temperatures.