Fermi level and bands offsets determination in insulating (Ga,Mn)N/GaN structures

TL;DR

This study determines the Fermi level and band offsets in (Ga,Mn)N/GaN structures using electroreflectance, revealing strong Fermi level pinning and potential for (Ga,Mn)N as a semi-insulating buffer layer in GaN-based devices.

Contribution

The paper provides the first detailed analysis of Fermi level positioning and band offsets in (Ga,Mn)N/GaN structures, highlighting their semi-insulating properties and potential applications.

Findings

Fermi level is pinned in the middle of the band gap in (Ga,Mn)N.

Band gap change mainly occurs in the valence band, about -0.028 eV per % Mn.

(Ga,Mn)N can serve as a semi-insulating buffer layer in heterostructures.

Abstract

The Fermi level position in (Ga,Mn)N has been determined from the period-analysis of GaN-related Franz-Keldysh oscillation obtained by contactless electroreflectance in a series of carefully prepared by molecular beam epitaxy GaN/Ga1-xMnxN/GaN(template) bilayers of various Mn concentration x. It is shown that the Fermi level in (Ga,Mn)N is strongly pinned in the middle of the band gap and the thickness of the depletion layer is negligibly small. For x > 0.1% the Fermi level is located about 1.25 - 1.55 eV above the valence band, that is very close to, but visibly below the Mn-related Mn2+/Mn3+ impurity band. The accumulated data allows us to estimate the Mn-related band offsets at the (Ga,Mn)N/GaN interface. It is found that most of the band gap change in (Ga,Mn)N takes place in the valence band on the absolute scale and amounts to -0.028+-0.008 eV/% Mn. The strong Fermi level pinning in the middle of the band gap, no carrier conductivity within the Mn-related impurity band, and a good homogeneity enable a novel functionality of (Ga,Mn)N as a semi-insulating buffer layers for applications in GaN-based heterostuctures.