The formation and thermal stability of multilayer ohmic contacts to n-GaAs with TiBx and Mo diffusion barriers

Thermal degradation of Au/Mo/TiB_x/AuGe multilayer ohmic contacts with Mo and TiB _x diffusion barriers was studied. The contacts were employed in Gunn-effect diodes. Depth profiling of the components in the contacts was performed using Auger electron spectroscopy. The microrelief of the metal/semiconductor interface and contact surface morphology were examined with atomic force microscopy and scanning electron microscopy, respectively. The measurements were taken before and after argon annealing at T=400, 600, or 800°C for 60 s. The resistance of the Gunn diode mesa was also measured. Annealing at 400°C is shown not to affect the sandwich structure of the contacts. Annealing at 600°C causes structure rearrangement in the layers up to cracking. It is found that the thermal threshold of degradation of the Au/Mo/TiB_x /AuGe/GaAs structure depends on the resistance of the TiB_x layer to thermal effects. Reasons for the degradation of Mo and TiB_x antidiffusion properties are discussed.