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HL: Halbleiterphysik

HL 24: GaN: Pr
äparation und Charakterisierung I

HL 24.7: Vortrag

Dienstag, 25. März 2003, 16:45–17:00, BEY/118

Electron Spin Resonance of Mn²⁺ in hexagonal wurtzite GaN and AlN films — •T. Graf¹, M. Gjukic¹, M. S. Brandt¹, O. Ambacher², and M. Stutzmann¹ — ¹Walter Schottky Institut, Technische Universität München, 85748 Garching — ²Zentrum für Mikro- und Nanotechnologien, Technische Universität Ilmenau, 98684 Ilmenau

We have investigated MBE-grown GaN:Mn and AlN:Mn layers with Mn doping concentrations around 10²⁰cm⁻³ with X-band Electron Spin Resonance spectroscopy. The observed resonances are consistent with isolated, axially distorted ⁵⁵Mn²⁺ centers with an isotropic Zeeman interaction with g=2.000 and hyperfine interactions A=−69 G. The observed axial crystal field D varies between −218 to −236 G depending on the biaxial strain in the GaN layers, and reaches −648 G in relaxed AlN films in agreement with Newman’s superposition model for small displacements from the substitutional Ga and Al sites. At intermediate orientations of the crystalline c-axis with respect to the magnetic field, intermixing occurs between the nuclear spin eigenstates due to off-diagonal elements in the spin Hamiltonian, which strongly enhances the transition probabilities of usually forbidden ESR transitions with |Δ m_i| > 0. However, unlike in GaAs:Mn²⁺ at similar doping concentrations, there is no evidence for electrostatic or magnetic coupling to extended valence band states, which is a prerequisite of ferromagnetic exchange required for spintronic devices.