Photogeneration of narrow quantum wells on ZnO surfaces

Visible-light illumination of accumulation layers on Zn0 surfaces produced by hydrogen-ion implantation at 80 K results in a substantial enhancement of the surface electron density, up to the enormous value of 6x10¹⁴ cm^-2. The photoenhanced layer persists indefinitely after the light is switched off, and has an effective width of 10-20 A. On the basis of the results presented we tentatively suggest that in addition to the fully-ionized proton donors responsible for the initial implanted accumulation layer, H₂⁺ ions are also introduced beneath the surface by the hydrogen implantation. Illumination dissociates these species and shifts the protons so produced into sites in which they become fully ionized, thus augmenting the surface electron density of the implanted surface.