Smooth ceramic titanium nitride contacts on AlGaN/GaN-heterostructures

Abstract

Two contact systems on AlGaN/GaN-heterostructures were investigated with respect to their electrical performance and surface morphology. The first system is a standard Ti/Al-based multilayer contact system, generally exhibiting an excellent electrical performance. However strong surface roughening and degradation after annealing due to high diffusion rates of aluminum and gold often occur, which in turn affect the contact stability and reliability. Thus, a contact system based on sputtered titanium nitride was studied. TiN is well known as a thermally stable material with a good conductivity, but is used only indirectly via thermal transformation of thin Ti layers in typical group III nitride circuits. Using the TiN contact system, we were able to achieve a competitive electrical performance with a minimum value of contact resistivity of 1.8 × 10−5 Ω cm2 at an annealing temperature of 850 °C for 45 s. Most importantly, the surface roughness was greatly reduced (maximum rms values of 1.8 nm). The contact formation via rapid thermal processing was studied using Auger electron depth profiling.