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In-vacancies in Si-doped InN

Christian Rauch 1Floris Reurings 1Filip Tuomisto 1Tim Veal 2Chris F. McConville 2Hai Lu 3William J. Schaff 3Chad S. Gallinat 4Gregor Koblmueller 4James S. Speck 4

1. Helsinki University of Technology, Department of Applied Physics (TKK), POB 1100, Otakaari 1 M, Espoo 02015-TKK, Finland
2. University of Warwick, Department of Physics, Gibbet Hill Road, Coventry CV4 7AL, United Kingdom
3. Cornell University, Electrical and Computer Engineering, Ithaca, NY 14853-540, United States
4. University of California, Santa Barbara, CA 93106, United States


Despite of remarkable improvements in crystal quality during the last years, as-grown InN still exhibits a strong n-type tendency and considerably high defect concentrations [1]. Concerning native defects, recent calculations [2] predict In-vacancies to be the most abundant defect type in n-type InN and possess the tendency for forming complexes with other intrinsic defects or impurities [3], which raises the question of their impact on the materials properties. In this contribution we present results obtained with positron annihilation spectroscopy in MBE-grown Si-doped InN with electron concentrations from 1 x 1018 cm-3 to 6.6 x 1020 cm-3. Temperature dependent Doppler Broadening measurements show In-vacancies in concentrations from 2 x 1016 cm-3 to 7 x 1017 cm-3 which increase with increasing electron concentration in the material. These values are remarkably higher than what can be estimated from theoretically predicted formation energies of In-vacancies in InN based on experimentally determined Fermi levels in the investigated samples [4]. Additionally, a strong inhomogeneity of the defect distribution with an increasing vacancy concentration towards the layer/substrate-interface can be observed. These results suggest that the formation energy of In-vacancies is locally reduced in the vicinity of extended defects, which are especially abundant in the interface area - possibly through the formation of defect complexes. From the observed threshold for the formation of In-vacancies, which is seen by a comparison with earlier results in He-irradiated InN [5], it can be deduced that in spite of their still relatively low absolute concentrations In-vacancies play an important role in reducing the electron mobility in the material.

[1] B. Monemar et al., Phys. Stat. Sol. B 244, 1759-1768 (2007)

[2] C. Stampfl et al., Phys. Rev. B 61, R7846-R7849 (2000)

[3] X. M. Duan et al., Phys. Rev. B 79, 035207 (2009)

[4] P. D. C. King et al., Phys. Rev. B 77, 045316 (2008)

[5] F. Tuomisto et al., Phys. Rev. B 75, 193201 (2007)


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Presentation: Oral at E-MRS Fall Meeting 2009, Symposium A, by Christian Rauch
See On-line Journal of E-MRS Fall Meeting 2009

Submitted: 2009-05-11 15:53
Revised:   2009-06-07 00:48