To form low-resistance Ohmic contact to p-type GaN, InGaN/GaN
multiple quantum well light emitting diode wafers are treated with boiled aqua
regia prior to Ni/Au (5 nm/5 nm) film deposition. The surface morphology of
wafers and the current–voltage characteristics of fabricated light emitting
diode devices are investigated. It is shown that surface treatment with boiled
aqua regia could effectively remove oxide from the surface of the p-GaN layer,
and reveal defect-pits whose density is almost the same as the screw
dislocation density estimated by x-ray rocking curve measurement. It suggests
that the metal atoms of the Ni/Au transparent electrode of light emitting diode
devices may diffuse into the p-GaN layer along threading dislocation lines and
form additional leakage current channels. Therefore, the surface treatment time
with boiled aqua regia should not be too long so as to avoid the increase of
threading dislocation-induced leakage current and the degradation of electrical
properties of light emitting diodes.
Source:IOPscience
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