Optical and electrical properties of semi-insulating GaN:C grown by MBE
- PDF / 73,333 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 62 Downloads / 198 Views
L10.7.1
Optical and electrical properties of semi-insulating GaN:C grown by MBE R. Armitage1,2, Qing Yang1,2, H. Feick3, S.Y. Tzeng1,2, J. Lim1,2, and E.R. Weber1,2 1
Dept. of Materials Science and Engineering, University of California, Berkeley CA 94720 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 3 Center of Advanced European Studies and Research (caesar), Bonn, Germany 2
ABSTRACT Semi-insulating wurtzite GaN:C of high optical quality is obtained with CCl4 or CS2 doping sources in plasma-assisted molecular-beam epitaxy in Ga-rich growth conditions. The highest resistivity (107 Ω-cm) is found for [C] in the low 1018 cm-3 range. An increasing fraction of carbon appears to form electrically inactive pair defects for higher doping levels causing the concentration of uncompensated residual donors to be higher in films with [C] in the 1019 cm-3 range compared with [C] in the 1018 cm-3 range. Blue (2.9 eV) and yellow (2.2 eV) luminescence bands are associated with carbon-related defects, and additional support is provided for the association of the blue luminescence with the carbon-acceptor deactivating pair defect. Finally, the temperature dependence of the resistivity is described within the grain-boundary controlled transport model of Salzman et al., Appl. Phys. Lett. 76, 1431 (2000). INTRODUCTION Carbon is a major residual impurity in GaN grown by metal-organic vapor phase epitaxy (MOVPE), and found practical use as an intentional dopant for semi-insulating GaN [1] and in ptype conducting zincblende GaN [2]. Despite this, understanding of the influence of carbon defects on GaN properties remains limited. Carbon could conceivably introduce several defect species: CN, CGa, and CI (interstitial). The calculated formation energies of these different defects are in fact similar [3]. Theory and experiment indicate that at low concentrations carbon forms predominately CN acceptors in ntype GaN [3,4]. However, some evidence suggests that a fraction of carbon exists as deep-level defects related to technologically important phenomena such as current collapse in field-effect transistors [5] and parasitic luminescence bands [6]. Few systematic studies were reported for carbon concentrations above 1018 cm-3. These either involved the metastable zincblende GaN phase [2], or utilized relatively poor-quality wurtzite material [7], obscuring the influence of carbon defects on GaN properties. EXPERIMENTAL DETAILS GaN epilayers of thickness ~1 µm were grown by MBE in a modified Riber 1000 system equipped with a gallium effusion cell and dc nitrogen plasma source. Semi-insulating (109 Ω-cm) MOVPE-GaN/sapphire templates were used as substrates. The carbon concentration was controlled by injecting CCl4 or CS2 vapor (Sigma Aldrich, 99.9%) into the chamber through a needle valve. The growth temperature was 750°C. Ga-rich conditions were maintained for all samples, confirmed by the presence of Ga droplets around the edges of the samples. The N-
L10.7.2
limited growth rates studied varied from
Data Loading...
