Distinct Photoinduced Wetting Transitions of Differently Doped GaN: An Indication of Collective Behavior

Water is a unique molecule made up of only three atoms. At room temperature, water molecules are linked together by hydrogen bonds; this arrangement is responsible for many unusual properties distinct from those of other liquids. We explore here the wetting behavior of water on gallium nitride (GaN) and reveal that UV irradiation promotes a wetting transition on n-type GaN but not on p-type GaN. A comprehensive investigation reveals that the oxygen impurities present in n-type GaN are responsible for the wetting transition. The photoluminescence (PL) and humidity-dependent behaviors also support the proposed explanation. In particular, an individual oxygen atom could affect ∼105 water molecules through the extended hydrogen bond network, which provides direct evidence that wettability by water molecules is a collective behavior.