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Photoluminescence of Zn-doped GaN grown by HVPE M. A. Reshchikov, D. Huang, and H. Morkoç Virginia Commonwealth University, Richmond, VA 23284, U.S.A. R. J. Molnar MIT Lincoln Laboratory, Lexington, MA 02420, U.S.A. ABSTRACT We investigated the behavior of photoluminescence (PL) in a wide range of temperatures and excitation intensities from Zn-doped GaN grown on c-plane of sapphire by hydride vapor phase epitaxy (HVPE). The low-temperature PL spectrum exhibited sharp peaks in the excitonic part with the full width at half maximum (FWHM) of about 5 meV. The peaks were attributed to free excitons and excitons bound to shallow donors and to Zn-related acceptors. A blue band with a maximum at 2.9 eV and FWHM of 0.33 eV dominated in the PL spectrum at low temperatures. We observed a significant UV shift (about 50 meV) of this band when the excitation density was increased from 10-6 to 100 W/cm2 or when the temperature of the sample was increased from 15 to 300 K. With increasing temperature, the blue band intensity quenched by 104 times in the range 180 - 250 K with the activation energy of about 0.64 eV. When the sample was illuminated from the substrate side, the blue band intensity dropped only 30 times in the temperature range of 180 - 340 K, and the activation energy did not exceed 0.25 eV. The PL spectrum of the GaN:Zn samples under investigation also contained broad red and green bands with maxima at about 1.8 and 2.4 eV, respectively. In PL from the substrate side, the blue and yellow (2.2 eV) luminescence dominated in the defect-related region of PL spectrum. Timeresolved PL measurements revealed nonexponential decay of the defect-related bands. INTRODUCTION GaN doped with Zn can be rendered semi-insulating, with room-temperature resistivity up to 1012 Ω cm, for high-power microwave devices [1]. In GaN, Zn introduces four acceptor like centers responsible for the broad bands peaking at 1.8, 2.2, 2.6 and 2.9 eV [2]. The most studied is the blue luminescence (BL) band that dominates the spectrum at moderate (

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