Investigating the Lateral Spreading of Vanadium Based Ohmic Contacts

Student’s Full Name: Fabiana P. Mayol López Student’s Home Institution: Ana G. Méndez University, Gurabo Campus. NNCI Site: CNF @ Cornell University REU Principal Investigator: Prof. Grace Xing - Department of MSE & ECE, Cornell University REU Mentors: Joseph Dill, Shivali Agrawal, Xianzhi Wei - Cornell University Abstract: Aluminum Gallium Nitride (AlGaN)-based electronics have emerged as strong candidates for next-generation power devices in recent years, due to their high breakdown voltage and superior thermal conductivity. Despite these intrinsic material advantages, a key challenge for high-performance AlGaN power devices is forming effective ohmic contacts, especially at high Aluminum compositions. Several studies have indicated that poor contact morphology can significantly degrade the performance of vanadium-based ohmic contacts to high AlGaN. However, the impact of annealing conditions and the choice of diffusion barrier metals on the lateral spreading of the alloy after annealing remains unexplored. Our research focuses on determining the annealing conditions that minimize the lateral spreading of vanadium-based ohmic contacts on Silicon for applications on aluminum gallium nitride (AlGaN) substrates. As reported in literature, aluminum nitride (AlN) PN diodes have often been shorted due to the spreading of the ohmic metals. The lateral spreading causes the metals to come in contact with each other or the n and p-layers to be shorted, allowing the electrons to take the path of least resistance and move in between the metals rather than through the designed semiconductor heterostructure. Our experiments were carried out on 8x8 mm silicon pieces with varying metal stacks while testing different annealing temperatures and the amount of time annealed in order to find the optimal condition that would cause the least amount of spreading. We characterized the amount of spreading and identified the metal causing the spreading using the CNF’s Zeiss Supra Scanning Electron Microscope (SEM) and the Bruker Quantax 200 Energy Dispersive Microscopy (EDS). The measurements were taken from circular transmission line model (C-TLM) and linear transmission line model (L-TLM) structures.