We have directly studied the elemental depth profiles of Au/Ti and Au/Pt/Ti multiple-layers, which are candidates as ohmic materials for a p-type diamond substrate, grown on diamond (001) surfaces at room temperature (RT) and 550 °C using Rutherford backscattering method. Significant interlayer diffusion between Au and Ti is observed for the samples without a sandwiched Pt layer, resulting in diffusion of some Ti atoms to the surface. On the other hand, the trilayer structure of Au/Pt/Ti forms a thermally stable electrode up to 1000 °C. It is also found that the interfacial TiC
x
layer grown at 550 °C is thicker than that deposited at RT followed by post-deposition annealing at 550 °C. The effective thickness of the Pt layer is estimated to be more than 20 nm to prevent Ti segregation to the surface.
The synchrotron radiation lithography process of grating fabrication for distributed feedback (DFB) laser diodes is described. By finely controlling the field size in electron beam writing of the X-ray mask, the grating period can be arbitrarily varied with an accuracy of less than 0.1 nm . Gratings of 0.24-µm period with a λ/4 shift are formed in the Ta absorber X-ray mask, and transferred to the laser substrate by SR exposure. This process is successfully applied to the fabrication of 20-wave-length DFB-LD arrays.
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