Optical Detection of Electron Nuclear Double Resonance on the Residual Donor in GaN
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Internet Journal o f
Nitride S emiconductor Research
Volume 1, Article 9
Optical Detection of Electron Nuclear Double Resonance on the Residual Donor in GaN F. K. Koschnick, K. Michael, J.-M. Spaeth Fachbereich Physik, University of Paderborn B. Beaumont, Pierre Gibart Centre de Recherche sur l'Hetero-Epitaxie et ses Applications, CRHEA-CNRS This article was received on June 2, 1996 and accepted on September 16, 1996.
Abstract Optically detected electron nuclear double resonance (ODENDOR) was measured in the 2.2 eV ‘yellow’ luminescence band associated with the residual donor in n-type undoped GaN. The ODENDOR lines are due to gallium and show a quadrupole splitting which can be described with an axial tensor. The quadrupole parameter was estimated to be q(69Ga) = 1/2 Qzz = 0.22 MHz. A hyperfine interaction for 69Ga of about 0.3 MHz for the isotropic and of about 0.15 MHz for the anisotropic part was estimated from the width of the ODENDOR lines. It is tentatively suggested that a Ga interstitial is the residual donor. Application of gallium nitride for optical devices in the near UV region requires a control of the native and extrinsic defects. Undoped MOVPE- and HVPE-grown GaN layers have high residual n-type conductivities with typically 10 17 cm-3 to 1019 cm-3 conduction electrons, exceeding the concentrations of impurities [1] [2]. This strongly suggests that the conductivity is due to native defects. The nature of the responsible residual donor has not been identified. It is often believed to be the N vacancy [1] [2] [3]. An EPR line with a halfwidth of about 0.5 mT was observed in nominally undoped, MOVPE-grown GaN and associated with the residual donor by correlated conductivity measurements [4]. The g values of the axial g tensor were determined to be g|| = 1.9515 and g^ = 1.9483. But no conclusion could be drawn from the structureless EPR line on the nature of the donor which was also observed with optically detected EPR (ODEPR) via the so called ‘yellow’ luminescence band at 2.2 eV [5]. We report on the first optically detected electron nuclear double resonance (ODENDOR) measurements on the residual donor in GaN. The nominally undoped GaN layers were grown on sapphire with MOVPE. The ODENDOR spectra were measured in the yellow luminescence as an intensity change of the ODEPR line of the donor at 1.5 K. ODENDOR was measured with cw microwave radiation and amplitude modulation (500 Hz) of the radio frequency [6]. In Figure 1 (upper trace) the ODENDOR spectrum is shown for B || c. The relative ODENDOR effect with respect to the luminescence intensity was about 2 X 10-5. We found ODENDOR signals only between 7 MHz and 14 MHz. The recording time of the spectrum was about 10 hours because of the extremely weak signals. The ODENDOR effect vanished for the magnetic field outside the sharp donor ODEPR resonance. Since the ODENDOR lines are centered about the Larmor frequencies of the two Ga isotopes (69Ga and 71Ga with abundancies of 60.1% and 39.9%, respectively, both with I = 3/2) it can be concluded that t
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