| dc.description.abstract | We have demonstrated the Schottky diodes performances for Au, Cu/Au, and Ni/Au contact to the InGaP layer. The Schottky barrier heights for the as-deposited samples of Au, Cu/Au, and Ni/Au metallic structures contact to the InGaP layer are 0.99, 0.99, and 0.93eV, respectively.
These Schottky diodes were thermal annealed in a RTA system to investigate the thermal stability. The metallic structure of Cu/Au was found to have a superior thermal stability than that of Au and Ni/Au contact to the InGaP layer. Following, the cross-sectional microstructures conducted from TEM observation were used to study the interface evolutions between metals and semiconductor and degradation mechanism for metals contacts to the InGaP. The metallic Au would indiffuse into the InGaP layer at annealed temperature of 300?C and tend to congregated to from huge Au-rich areas with increasing the annealing temperature. However, the metallic Cu was more stable and indiffused into the InGaP layer as the annealing temperature reaching 500?C. The indiffusion of Cu is more uniform than that of Au and a form an obvious sublayer in the original InGaP layer. This was attributed to the superior thermal conductivity and lower electronmigration resistance of the metallic Cu.
The measurement results of AFM, SEM, XRD, TEM, and AES depth profile were also used to analyze the degradation mechanisms. We found that Cu layer was unstable and completely released as annealing temperature reached 500oC. The metallic Cu would react with the metallic Au layer to form a Cu3Au2 intermetallic layer and indiffuse into the InGaP layer to create the CuP2 binary alloy. Therefore, we concluded that the thermal degradation mechanism of Cu/InGaP Schottky contacts was due to the release and indiffusion of the element Cu, and the subsequent formation of the CuP2 binary alloy.
Furthermore, we also calculated the reaction parameters for Cu indiffusing into the InGaP layer. The indiffusion of Cu into the InGaP layer would form a sublayer and the thickness also increased with increasing annealing temperatures and times. From the relationship between the sublayer thickness and annealing times, we could determine the activation energy of the CuP2 binary alloy was 0.93eV and the diffusion constant was also found to be 1.37 ? 103 nm2/s at annealing temperature of 500?C.
Eventually, to improve the thermal stability for the Schottky diodes, the refractory metal of W was employed as a diffusion barrier layer between the Cu and InGaP layer. Combined with AFM and TEM measurement results, a thin W layer deposited between the Cu and InGaP layer could effectively obstruct the indiffusion of Cu into the InGaP layer at annealing temperature of 550oC for 1 min. | en_US |