Depletion region width of a ferroelectric heterostructure interface by surface potential measurements under illumination

A method for measuring the depletion region width at oxide heterostructure interfaces is developed. It is demonstrated on bismuth ferrite--chromite thin films that exhibit p-type behavior and form a p--n-like junction when grown on a Nb-doped strontium titanate substrate. Using surface photovoltage measurements with Kelvin probe force microscopy under illumination on films of different thicknesses, a maximum SPV response is identified, revealing the depletion region width. This width also enables estimation of the acceptor concentration in the film, providing a non-destructive approach to probing ferroelectric heterostructures.