Dresden 2003 – wissenschaftliches Programm

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HL: Halbleiterphysik

HL 29: GaN: Pr
äparation und Charakterisierung II

HL 29.3: Vortrag

Mittwoch, 26. März 2003, 15:00–15:15, BEY/118

The Mn^3+/2+ acceptor level in group III nitrides — •M. Gjukic¹, T. Graf¹, M. Buschbeck¹, 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

A large potential for novel device applications is anticipated for GaMnN with strong ferromagnetic interactions between the Mn²⁺ spins, which are possibly mediated by extended valence band states. We have investigated MBE-grown GaN:Mn and AlN:Mn layers with Mn doping concentrations around 10²⁰cm⁻³, as measured by ERD and SQUID magetization. Unless additional electrons are provided via codoping with similar concentrations of Si, the total Mn concentration exceeds the concentration of substitutional Mn_Ga²⁺, as measured by ESR, by far. Therefore, in pure GaN:Mn films Mn is mostly present in the neutral Mn³⁺ acceptor state, and the Mn-related optical absorption band at 1.5 eV in GaN:Mn and AlN:Mn must be ascribed to spin-allowed Mn^{3+ 5}E→ ⁵T internal absorption processes. Based on photoconductivity measurements in GaN:Mn, another absorption band observed in GaN:Mn (AlN:Mn) with an onset of 1.8 eV (2.6 eV) is assigned to the direct optical ionization of neutral Mn³⁺ acceptors. As the Mn³⁺ acceptor level is located about 1.8 eV (2.6 eV) above the valence-band edge of GaN (AlN), the nature of both acceptor wave functions is very different from an effective-mass-like Mn²⁺–h⁺ complex, and the realization of carrier-mediated ferromagnetism seems rather unlikely in GaN:Mn.