Influence of semiconductor surface preparation on photoelectric properties of Al–Zn3P2 contacts

The Schottky barriers formed by Al on Zn3P2 p-type crystals have been studied. Three types of crystals (monocrystal, large-grain crystal and polycrystal) were used for device fabrication. The samples were separated in two groups according to the type of structure and the methods of surface preparation. The samples from the first group were different in structure (monocrystal, large-grain crystal and polycrystals) but prepared in the same way. Three polycrystals with differently prepared surfaces were collected in the second group. Two samples from this group were also annealed in open air at 523 K for 24 h. Measurements of photovoltaic effect at room temperature were carried out to test the impact of surface preparation on photoelectric properties of Al–Zn3P2 contacts. Substantial differences in shape and intensity of PV signal were observed depending on whether the surface of semiconductor was mechanically polished, chemically etched or/and heat treated. The height of potential barrier, ΦB, and optical transitions in semiconductor were determined. The value of ΦB changed from 0.747 to 0.767 eV for unheated samples and from 0.724 to 0.755 eV for the heated ones. The quality of semiconductor surface seems to have an essential influence on spectral characteristics of Al–Zn3P2 junctions, especially in the case of polycrystals. It appeared that thorough preliminary mechanical polishing of crystals surface provides quite good photoelectric properties of Al–Zn3P2 junctions.