Wet etching of ion-implanted GaN crystals by AZ-400K photoresist

The photoresist developer AZ-400K, commonly used to remove AW encapsulant l ayers on GaN crystalline films, is found to also etch certain as-grown GaN films. Even as-grown GaN films, which can not be etched in AZ-400K, however can be etched if amorphized by ion implantation. Etch rates of as high as 450 Angstrom /min. were observed. The etching proceeds linearly in GaN in t he first few minutes to a depth corresponding to the depth of the amorphous region. Subsequently, the etching rate saturates. Annealing of the highly amorphized samples up to 1000 degreesC for one minute in a N-2/H-2 gas mixt ure does not reduce the etch rate, but for lower doses we observed a reduct ion of the etch rate. Observations of etching depth under various ion-impla nted conditions could be correlated with the number of displacements per at oms (dpa) required for amorphization.