The Effect of Technological Factors on the Characteristics of Ohmic Contacts of the Power AlGaN/GaN/SiC-HEMT

Abstract

The effect of the microrelief, dislocation structure, and other defects of epitaxial layers in the source and drain regions of a Nitride High Electron Mobility Transistor (НЕМТ) on the parameters of the formed ohmic contacts is discussed. The investigations are carried out directly on the chips of power microwave transistors manufactured on the GaN/AlGaN/GaN/SiC heterostructures. The ohmic fired contacts are formed with the use of Ti–Al–Mo–Au and Ti–Al–Ni–Au compositions. The microrelief of the surface on the interface of the fired contact/AlGaN and the defects formed on it is investigated in order to estimate the structural features of the contact areas. It is found that the resistance of the source and drain regions are determined to a considerable extent by the microstructure of the surface on the boundary. The formation of the conductive layer in AlGaN under an ohmic fired contact is shown by the experiments. The possibility of the formation of a new type of structural defect with a high aspect ratio in the contact and active areas of the devices at the formation of ohmic fired contacts is demonstrated. It is shown that the existence of high densities of such defects results in an increase of the leakage currents of the devices.