Electrical and Optical Properties of Carbon Doped Cubic GaN Epilayers Grown Under Extreme Ga Excess
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Y8.2.1
Electrical and Optical Properties of Carbon Doped Cubic GaN Epilayers Grown Under Extreme Ga Excess D. J. As, D.G. Pacheco-Salazar∗, S. Potthast, and K. Lischka, University of Paderborn, Faculty of Science, Department of Physics, Warburger Strasse 100, D-33095 Paderborn, Germany, [email protected]
ABSTRACT P-type doping of cubic GaN by carbon is reported with maximum hole concentration of 6.1x1018cm-3 and hole mobility of 23.5 cm2/Vs at room temperature, respectively. The cubic GaN:C was grown by rf-plasma assisted molecular beam epitaxy (MBE) under Ga-rich growth conditions on a semiinsulating GaAs (001) substrate (3 inches wafer). E-beam evaporation of a graphite rode with an C-flux of 1x1012cm-2s-1 was used for C-doping of the c-GaN. Optical microscopy, Hall-effect measurements and photoluminescence were performed to investigate the morphological, electrical and optical properties of cubic GaN:C. Under Ga-rich growth conditions most part of the carbon atoms were incorporated substitutially on N-site giving p-type conductivity. Our results verify that effective p-type doping of c-GaN can be achieved under extrem Ga excess.
INTRODUCTION Among possible alternative acceptor dopants in GaN especially carbon has received considerable interest due to its similarity to nitrogen in atomic radius and electronegativity [1-3]. Previous experiments by Abernathy et al. [1] showed p-type doping of GaN by carbon grown by metal organic molecular beam epitaxy (MOMBE) on GaAs substrates. However, due to the use of CCl4 a pronounced reduction in growth rate prohibited the incorporation of higher C concentrations and the maximum hole concentration reached was 3 x 1017 cm-3. Armitage et al. [4] demonstrated that the reduced growth rate could be compensated by suppling high Ga fluxes, however no higher hole concentrations was achieved. Recently, we have shown that C is indeed the most shallow acceptor in cubic GaN with a binding energy of about 215 meV [5]. Unfortunately due to self-compensation effects the hole concentration saturated and then decreased with increasing C-flux under stoichiometrical growth conditions. A CI-CN complex is most likely responsible for the observed compensation [6]. To avoid the formation of this complex Ga-rich growth conditions are proposed to increase the incorporation of C at the N substitutional site [7]. In this contribution we report in detail on the incorporation of C in cubic GaN under extrem Ga-rich growth conditions. Optical microscopy, Hall-effect measurements and temperature dependent photoluminescence (PL) are used for characterization. A record hole concentration and hole mobility as high as 6.1x1018 cm-3 and 23.5 cm2V-1s-1, respectively is measured. This behavior clearly indicates that Ga-rich conditions are advantageous for improved p-type doping.
∗
On leave from Universitade de Sao Paulo, Sao Paulo, Brazil
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EXPERIMENTAL Carbon doped cubic GaN epilayers were grown by rf-plasma-assisted MBE on semi-insulated GaAs (001) wafers (3 inch) at 720°C. Carbon doping was acco
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