To improve the thermal stability of Schottky performances, a refractory diffusion barrier layer of W is used for impeding the indiffusion of Cu into the InGaP layer. From the atomic force microscopy measurements for W/Cu Schottky contacts to the InGaP layer thermally annealed at various temperatures, both the surface roughness and mean particle size increase with increasing annealing temperatures. Meanwhile, there is also an obvious change in the surface color for the Schottky diodes thermally annealed at 500°C. This change in surface color reveals that the metallic Cu is unstable and tends to react with the ambient nitrogen as annealing temperature reaches 550°C. However, transmission electron microscopy measurement represents a well-defined W layer between the Cu and InGaP layer under annealing temperature of 550°C. The interface of W/InGaP is obvious and no indiffusion of Cu appears in the InGaP layer. Therefore, the metallic W acts as a diffusion barrier layer and results in a higher thermal stability of Schottky performance. As annealing temperature reached 600°C, an obvious spike-toothed indiffusion appears around the W/InGaP interface. According to energy dispersive X-ray spectroscopy analyses, the spike-toothed region is attributable to the penetration of Cu into the InGaP layer through the grain boundaries of W, and results in the degradation of the Schottky performance.
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