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

Area of Science:

• Solid State Physics
• Materials Science
• Semiconductor Physics

Background:

• Understanding the electronic properties of dilute magnetic semiconductors like (Ga,Mn)N is crucial for advanced electronic and spintronic applications.
• The position of the Fermi level and band offsets significantly influence carrier behavior and device performance in semiconductor heterostructures.

Purpose of the Study:

• To determine the Fermi level position in (Ga,Mn)N using contactless electroreflectance.
• To investigate the impact of Manganese (Mn) concentration on the electronic band structure of GaN.
• To explore the potential of (Ga,Mn)N as a semi-insulating buffer layer in GaN-based heterostructures.

Main Methods:

• Preparation of GaN/Ga$_{1-x}$Mn$_{x}$N/GaN(template) bilayers using molecular beam epitaxy with varying Mn concentrations (x).
• Analysis of Franz-Keldysh oscillations in contactless electroreflectance spectra to determine Fermi level and band structure.
• Calculation of Mn-related band offsets at the (Ga,Mn)N/GaN interface.

Main Results:

• The Fermi level in (Ga,Mn)N is strongly pinned near the middle of the band gap, with a negligible depletion layer thickness.
• For Mn concentrations (x) > 0.1%, the Fermi level is located 1.25-1.55 eV above the valence band, below the Mn$^{2+}$/Mn$^{3+}$ impurity band.
• The band gap change in (Ga,Mn)N primarily occurs in the valence band, with a rate of -0.028 ± 0.008 eV/% Mn.

Conclusions:

• The strong Fermi level pinning, lack of conductivity in the Mn impurity band, and good homogeneity make (Ga,Mn)N suitable as a semi-insulating buffer layer.
• This finding opens possibilities for novel functionalities in GaN-based heterostructures and devices.
• (Ga,Mn)N's unique electronic properties facilitate improved device performance and integration.