p-doping of GaN by MOVPE
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Internet Journal o f
Nitride S emiconductor Research
Volume 2, Article 37
p-doping of GaN by MOVPE S. Haffouz, B. Beaumont, M. Leroux, M. Laugt, P. Lorenzini, Pierre Gibart Centre de Recherche sur l'Hetero-Epitaxie et ses Applications, CRHEA-CNRS L.G.Hubert-Pfalzgraf Laboratoire de Chimie Moléculaire,Faculté des Sciences, Nice, France This article was received on July 2, 1997 and accepted on September 16, 1997.
Abstract Mg has been widely used as p-doping species despite its intrinsic difficulties. It is nowadays well established that during the growth process of Mg doped GaN, atomic H is generated from the decomposition of NH3 and Mg-H complexes are formed in the layer. This has been for instance shown by the occurrence of LO mode in IR absorption, and by the observation of the Mg-H local vibration modes. This H passivation limits the electrical activity of Mg, therefore an activation process is required to get full activation of the Mg atoms. In the present study, bismethylcyclopentadienyl magnesium [(MeCp) 2Mg] was used as precursor. However, this precursor reacts in the gas phase with NH3 to produce tiny solid particles as evidenced by a very bright diffuse emission visible along the laser beam used for reflectometry measurements. This simplest obvious product would be [(MeCp)Mg(NH2)]m (m≥2). To limit this drawback, Ga and Mg precursor lines have been separated. With proper in situ heat treatment, doping densities up to 1.5x1018 cm-3 have been obtained. PL spectra of lightly Mg doped samples (1016 cm-3) are dominated by shallow donor-acceptor pairs whereas for higher doping densities ( 1018 cm-3), the luminescence is dominated by a broad band in the 2.7-2.9 eV range. GaN LEDs were fabricated from Si doped (n-type) and Mg-doped (p-type) GaN, these LEDs emit in the blue-UV range.
1. Introduction Because of their direct wide band gap, III-V nitrides are of great interest due to their applications in short-wavelength optical devices, or high power and high frequency electronic devices [1]. The successful development of short wavelength light emitting diodes and the most recent realisation of nitride semiconductor lasers have stimulated great interest in the application of this material for blue and ultraviolet optoelectronic devices. P-type conductivity in GaN is the key for producing the optoelectronics devices. Mg has been widely used [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] despite its intrinsic difficulties. It is nowadays well established that during the growth process of Mg doped GaN, atomic H is generated from the decomposition of NH3 and Mg-H complexes are formed in the layer [3] [4] [5]. This has been for instance shown by the occurrence of LO mode in IR absorption, and recently by the observation of the Mg-H local vibration modes (LVM) [4] [14]. Measurements of depth profiles showed that Mg and H are incorporated simultaneously [15]. This H passivation limits the electrical activity of Mg, therefore an activation process is required to get full electrical activity of the Mg atoms. Previous
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