Surface potential barrier in m-plane GaN studied by contactless electroreflectance

Abstract

Contactless electroreflectance (CER) is used to study the surface potential barrier in m-plane GaN UN+ [GaN ( nm)/GaN:Si] structures grown by using molecular beam epitaxy. Clear bandgap-related transitions followed by Franz–Keldysh oscillations (FKO) have been observed in the CER spectra of all samples at room temperature. The built-in electric fields in the undoped cap layers have been determined from the FKO period. From the built-in electric field and the undoped GaN layer thickness, the Fermi level location at the air-exposed m-plane GaN surface has been estimated as 0.42 ± 0.05 eV below the conduction band.