Yellow luminescence in Mg-doped GaN
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Internet Journal o f
Nitride S emiconductor Research
Volume 2, Article 28
Yellow luminescence in Mg-doped GaN F. J. Sánchez, F. Calle, D. Basak, J. M. G. Tijero, M. A. Sánchez-García, E. Monroy, E. Calleja, E. Muñoz Dpt. Ingeniería Electrónica, E.T.S.I. Telecomunicación, Politécnica, Ciudad Universitaria B. Beaumont, Pierre Gibart Centre de Recherche sur l'Hetero-Epitaxie et ses Applications, CRHEA-CNRS J.J. Serrano, J.M. Blanco Dpt. Ingeniería Electrónica, E.T.S.I. Telecomunicación, Politécnica, Ciudad Universitaria This article was received on June 11, 1997 and accepted on September 12, 1997.
Abstract Optical thresholds, that correspond to a level located at 1 eV above the valence band, are observed by photocapacitance techniques in n-type Mg-doped GaN. In undoped GaN, this level has been previously related to the yellow emission detected by photoluminescence. In Mg-doped GaN, this yellow luminescence is only observed for excitation energies below the Mg-related band (2.9 - 3 eV). This result evidences that Mg-doping may reduce but not avoid the formation of the yellow band related defects in n-type and semiinsulating Mg-doped samples. The fact that the yellow luminescence is not observed for excitation energies above the bandgap may be justified by a higher efficiency of the Mg-related recombination path.
1. Introduction The group III nitrides technology has reached in the recent years a great development in the short-wavelength emitting devices field. The first blue cw laser operating at room temperature has been demonstrated [1]. Concerning blue and UV emitters, care must be paid to non radiative recombinations or alternative radiative recombination paths, which may be detrimental to the device performance. This may be the case of the yellow luminescence, a broad band centered at 2.2 eV, which is observed in undoped and n-type doped GaN, regardless the growth technique used. This emission was interpreted by Ogino and Aoki [2] and later by Hofmann et al. [3] as a transition from a shallow donor to a deep acceptor located at about 1 eV above the valence band (VB). Recent experimental and theoretical results support this model [4] [5] [6] [7]. Several authors have reported on the reduction of the yellow band in n-doped GaN, like Nakamura et al. that observed a moderate decrease of the absolute intensity of the yellow band in Ge and Si doped samples [8]. The yellow emission can also be reduced and even suppressed by doping with Mg [9], or growing on Ga-rich conditions [10]. Neugebauer and Van de Walle suggest from first principles calculations that the yellow emission is related to a deep level generated by a complex defect involving Ga vacancies [7], whose formation energy increases in semiinsulating or p-type GaN. That result would explain the abscence of the yellow band in highly Mg-doped GaN [9]. In this work, photocapacitance measurements of Mg-doped GaN are performed over a photon energy range of 0.5 to 3.5 eV, to study the presence of deep levels. The results are compared with photoluminescence (PL) sp
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