Work function tailoring in gallium phosphide nanowires

• The work function of polytypic GaP nanowires was studied via Kelvin probe microscopy. • The work function is different for wurtzite (4.2 eV) and zinc blende (4.34 eV) GaP. • Flat defects act like wurtzite insets decreasing the work function of zinc blende GaP. • Sub-monolayer arsenic shell increases the work function up to 4.75 eV. In this work we investigate effects of the crystal phase, twinning defects and shell formation on the work function distribution over the surface of axially heterostructured GaP/GaPAs/GaP nanowires via frequency-modulated Kelvin probe force microscopy. Analysis of experimental data is supported by theoretical model based on density functional theory and Schrodinger–Poisson calculations. The study revealed that the work function of pure (110) ZB and ( 11 2 ¯ 0 ) WZ GaP is 4.34 eV and 4.20 eV respectively. The work function is found to be sensitive to the lattice twinning period which can additionally shift it between the value of WZ and ZB. Formation of a sub-monolayer thick GaPAs shell results in drastic increase of the work function (up to 4.75 eV). Thus, in this work we introduce several techniques for manipulating GaP nanowire work function. The ability to distinguish different crystal phases of the same material by means of Kelvin probe microscopy is shown for the first time.