Hydration effects in the photoassisted wet chemical etching ofgallium nitride

摘要

In this paper, we report a pH dependent study of the wet chemicalnetching of unintentionally doped n-type gallium nitride (GaN) layersngrown on sapphire substrates. When illuminated from a 253.7-nm mercurynline source, etching of GaN is found to take place in aqueous potassiumnhydroxide (KOH) solutions of pH values ranging from 11 to 15. Thenmeasured GaN etch rate reveals a peak value of 90 nm/min at pH=14.25 andndrops rapidly on both sides of the peak position. The etch effect ceasesnin KOH/ethanol solutions of similar molarities. These observations arenattributed to a hydration related phenomenon in which competing effectsnfrom free water molecules (H2O)f and hydroxyl ionsn(OH-) result in a peak etch rate. Our analysis indicates thenslowly falling tail of the GaN etch rate in the dilute pH regime isncharacterized by a (H2O)f dominant process whilenthe fast variation of etch rate at pH>14 is due to a competitionnbetween (H2O)f and OH-. PACS numbers: 68.55.Jk,n73.50.Pz, 81.65.Cf, 81.65.Hq