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Abstract. In this paper are considers the effect of the microrelief, dislocation structure and other defects of the epitaxial layers of the source and drain regions of the nitride HEMT transistors on the parameters of the formed ohmic contacts. The studies were carried out directly on high−power microwave transistors made of GaN/AlGaN/GaN/SiC heterostructures. Ohmic burning contacts were formed using the compositions Ti—Al—Mo—Au and Ti—Al—Ni—Au. To estimation the structural features of the contact areas, the surface microrelief at the interface of the burned contact/AlGaN and the defects formed on its surface was studied. It is shown that the resistance of the source and drain regions is largely determined by the surface microstructure at the boundary. Experimentally shown is the formation of a conducting layer in AlGaN under the ohmic contacts. The possibility of the formation of a new type of structural defects with a high aspect ratio in the contact and active areas of the devices during the formation of ohmic burned contacts is demonstrated. It is shown that the appearance of high densities of such defects leads to an increase of the device leakage currents.

The effect of parameters of plasma enhanced chemical vapor deposition (PECVD) processes for SiNx film fabrication on the electrical parameters of dielectric/АlGaN/GaN structures has been studied. The effect of growing film composition, additional heterostructure surface treatment with nitrogen plasma before dielectric deposition and HF biasing during treatment on the parameters of the С–V and I–V curves of SiNx/АlGaN/GaN structures has been analyzed. We show that films with nitrogen to silicon concentration ratios of 60 and 40% and a high oxygen content exhibit a decrease in the positive fixed charge in the structures although the I–V curves of the structures exhibit current oscillations. Information has been reported on the effect of PECVD process mode on current oscillation parameters, e.g. period and amplitude, and length of I–V curve section in which oscillations occur. Possible explanation of these oscillations has been suggested. Additional nitrogen plasma treatment of heterostructure surface before monosilane supply to the chamber changes the magnitude and sign of fixed charge and reduces the free carrier concentration in the 2D gas channel of SiNx/АlGaN/GaN heterostructures. Experimental evidence has been provided for the effect of PECVD process parameters and surface preparation on the electrical parameters of the heterostructures grown.

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