The etching of GaP, whether in strong HNO 3 or in strong HCl is severely inhibited, whereas mixtures of HNO 3 /HCl are commonly employed as etchants for chemical polishing. The etching mechanism of n-GaP in aqua regia (3HCl/ 1HNO 3 ) has been investigated. Aqua regia etching may occur by accomplishing both the following two processes:(1) oxidation and (2) dissolution. First, the nascent chlorine and nitrate ions obtained from the vigorous interaction between HCl and HNO 3 , may easily oxidize the surface atoms of GaP, then nucleophilic attacked by Cl ) on the electron-poor trivalent gallium ions of the oxide lattice generally takes place over the passive surface. Moreover, the remaining phosphate or phosphorus oxide is very soluble. Ga and P atoms are thus carried away from the surface by the etchant system. In HNO 3 -etch, the nitrate ion formed is a weak nucleophile and the amount of its production is very small. In the HCl-etch, Cl ) causes a direct attack on GaP substrate via an Ga (I) chloro intermediate whose thermodynamics is very unfavorable. Thus, the experimental observations are in good agreement with the mechanistic concepts presented.

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