Influence of the Mg precursor on the incorporation of Mg in MOVPE grown GaN.
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Internet Journal Nitride Semiconductor Research
Influence of the Mg precursor on the incorporation of Mg in MOVPE grown GaN. P. de Mierry1, B. Beaumont1, E. Feltin1, H.P.D. Schenk1, Pierre GIBART1, F. Jomard2, S. Rushworth3, L. Smith3 and R. Odedra3 1Centre
de Recherche sur l'Hétéroépitaxie et ses Applications, CRHEA-CNRS, de Physique des Solides de Bellevue, LPSB-CNRS, 3Epichem Limited, 2Laboratoire
(Received Friday, May 26, 2000; accepted Saturday, July 22, 2000)
Incorporation of Mg in metalorganic vapour phase epitaxy (MOVPE) GaN has been investigated, using two different Mg precursors: bis-methylcyclopentadienyl magnesium [(MeCp)2Mg] and Solution bis-cyclopentadienyl magnesium [Solution Cp2Mg]. SIMS analysis reveals an increased (two fold) efficiency of Mg incorporation for Solution Cp2Mg as compared to (MeCp)2Mg. These results are attributed to the stronger interaction of (MeCp)2Mg with NH3, leading to the formation of alkylmagnesium amine adducts, and a reduced effective Mg surface concentration. A decreased GaN growth rate with increasing Mg fluxes is also reported for both precursors. This effect is more pronounced for Solution Cp2Mg indicating that incorporation of Mg in the lattice proceeds via the capture of Mg into group III sites, and that the supply of Mg from the surface is reduced in the case when (MeCp)2Mg is used.
1 Introduction Among the group II elements, magnesium (Mg) is the only efficient species used as p-type dopant in MOVPE grown GaN [1] [2] . Incorporation of Mg in GaN is typically achieved via bis-cyclopentadienyl magnesium Cp2Mg [3] [4]. The alternative precursor bis-methylcyclopentadienyl magnesium, (MeCp)2Mg, was in comparison less employed [5] [6] [7] although it offers advantages over the Cp2Mg source because of its lower melting point and higher vapour pressure. In this article, we report on a comparative study of Mg incorporation in GaN, using Solution Cp2Mg and (MeCp)2Mg. A solution of the solid Cp2Mg source was employed to increase transport efficiency and reliability of delivery for this precursor. 2 Experimental The Mg concentration in GaN was measured by SIMS (CAMECA IMS4F) using a O2+ primary ion beam. Calibration was made with a Mg-implanted standard of known magnesium content. The sample’s structure consisted of a 1.5 µm thick undoped GaN deposited on sapphire (0001), a thin insulating layer of AlN (80 nm), and
a 0.8 µm Mg-doped GaN. The growth process was carried out in a home-made vertical reactor operating at 30 KPa [8].The growth temperature was 1090°C. Trimethylgallium (TMG), and either Solution Cp2Mg or (MeCp)2Mg, manufactured by Epichem, were used as the Ga and Mg sources. These elements were transported with a N2 carrier gas at a flow rate of 2 slm. A mixture of NH3 (2 slm) and N2 (2 slm) was introduced in the reactor by a separate inlet. The V/III ratio was 2200. Mg-doped GaN films were grown with a constant TMG flow rate of 40 µmol/min, while the Mg sources flow rates were varied between 80 nmol/min and 0.4 µmol/min. These values were determined from the eq
