Identification of Transition Metals in GaN
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crystal growth. In this paper we focus on three luminescence centers in GaN which show no-phonon (NP) lines peaking at 1.3 eV, 1.19 eV, and 1.047 eV and characteristic phonon replica. EXPERIMENTAL The GaN samples were grown by means of high temperature vapor phase epitaxy (HTVPE) [5] or by a modification of the sandwich technique [6]. Both techniques utilize liquid metallic Ga and NH 3 as precursors. The main characteristics are the small distances between the Ga melt and the substrates (_5 5 mm) and the high growth temperature around 1200 0 C. Doping of the GaN with transition metals was done by adding the respective transition metal in a ratio of 1:1000 to the Ga melt. The films were deposited either on (0001) 6H-SiC or (0001) sapphire substrate. The PL measurements were performed using a BOMEM DA8.02 Fourierspectrometer. The PL excitation (PLE) measurements were performed with conventional monochromator technique. For all the measurements a Ge-detector was used. RESIDUAL 3d TRANSITION METALS IN GaN Figure 1 shows a near infrared PL spectrum of a GaN sample grown by the sandwich technique on 6H-SiC. We observe three NP lines with transition energies at 1.3 eV, 1.19 eV, and 1.047 eV and their corresponding phonon sidebands. In the inset a detailed spectrum of one of the samples in the range of the 1.047 eV emission is depicted. In addition to the 1.047 eV emission, labelled A, further weaker emissions appear which are caused by so far unidentified defects. 491 Mat. Res. Soc. Symp. Proc. Vol. 395 0 1996 Materials Research Society
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Energy (eV) FIG. 1. PL spectrum of GaN/6H-SiC1in the near infrared region. Three NP lines peaking appear. The 1aN related phonon sidebands at 1.3 eV, 1.19 eV, and 1.047 eV together with inset shows a detailed spectrum of another sample in the range of the 1.047 eV transition. In some of the samples additional luminescence lines indicated by the arrows appear. They are caused by further contaminations and complexes. The Fe 3+ 4T1 -+ 6A1 in GaN (1.3 eV) The emission at 1.3 eV was first reported by Maier et al.[2]. Based on EPR-, PL-, and ODMR this emission was assigned to the electronic spin-flip transition between the 3 6 4 has been confirmed using T1 excited state and A1 ground state of Fe +. This attribution 6 spectroscopy showing the typical splitting of the A1 ground state [11, 12]. However Zeeman 3 the excitation mechanism of the Fe + luminescence is not established yet. Only in some of 3 line of the Ar ion laser. our samples we can excite the Fe + emission with the 514 nmthegreen Fe3+ emission. For instance Thus, most definitel different defects are involved to excite ie at 2.2beV c band yellow the of spectrum excitation theluminescence samples in some 3 has to be considered as with the excitation spectrum of Fe +. Excitation via the3 substrate 2 well. Therefore the bandoffsets determined from the Fe +/ + levels by Baur et al. [4] have with care. measurements we searched for the internal electron
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