Thermal Annealing Effect on Electrical and Structural Properties of Tungsten Carbide Schottky Contacts on AlGaN/GaN heterostructures

TL;DR

This study investigates how thermal annealing affects the electrical and structural properties of tungsten carbide Schottky contacts on AlGaN/GaN heterostructures, revealing changes in barrier height, leakage current, and interfacial chemistry.

Contribution

It provides new insights into the effects of annealing temperature on WC/AlGaN contacts, highlighting the formation of interfacial layers and their impact on device performance.

Findings

Barrier height decreases with higher annealing temperatures.

Interfacial W-O-C layer forms at 800°C, affecting electrical properties.

Oxygen distribution influences resistivity and leakage current.

Abstract

Tungsten carbide (WC) contacts have been investigated as a novel gold-free Schottky metallization for AlGaN/GaN heterostructures. The evolution of the electrical and structural/compositional properties of the WC/AlGaN contact has been monitored as a function of the annealing temperature in the range from 400 to 800{\deg}C. The Schottky barrier height ($\Phi$B) at WC/AlGaN interface, extracted from the forward current-voltage characteristics of the diode, decreased from 0.8 eV in the as-deposited and 400{\deg}C annealed sample, to 0.56 eV after annealing at 800 {\deg}C. This large reduction of $\Phi$B was accompanied by a corresponding increase of the reverse bias leakage current. Transmission electron microscopy coupled to electron energy loss spectroscopy analyses revealed the presence of oxygen (O) uniformly distributed in the WC layer, both in the as-deposited and 400{\deg}C annealed sample. Conversely, oxygen accumulation in a 2-3 nm thin W-O-C layer at the interface with AlGaN was observed after the annealing at 800 {\deg}C, as well as the formation of W2C grains within the film (confirmed by X-ray diffraction analyses). The formation of this interfacial W-O-C layer is plausibly the main origin of the decreased $\Phi$B and the increased leakage current in the 800{\deg}C annealed Schottky diode, whereas the decreased O content inside the WC film can explain the reduced resistivity of the metal layer. The results provide an assessment of the processing conditions for the application of WC as Schottky contact for AlGaN/GaN heterostructures.