This paper report effects of variation spacing of mesa isolation on pHEMT substrate in order get an optimum isolated area. The multilayer pHEMT substrate was used as a substrate and wet etching techniques have been applied to form the islands. The citric mixture used is C{sub}2H{sub}8O{sub}7:H{sub}2O{sub}2:H{sub}2O with ratio of 4:1:1. The mesa spacing used in this study was varies at 570, 792 and 835 μm. The etch time for each spacing was fixed at 3 minutes. The electrical effect of mesa isolation spacing was characterized through current-voltage curve. It was found that the 570 μm mesa spacing shows optimum current value for mesa isolation. This indicated that 570 μm mesa spacing etch with citric acid mixture of 4:1:1 ratio for 3 minutes etch time can produce optimum current for application of pHEMT device.
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