Growth and transport properties of p-type GaNBi alloys
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Sergei V. Novikov School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom
Zuzanna Liliental-Weber Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720
Roberto dos Reis Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720; and Instituto de Física, UFRGS, Porto Alegre, RS 15051, 91501-970 Brazil
Jonathan D. Denlinger Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720
Junqiao Wu and Oscar D. Dubon Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720; and Department of Materials Science and Engineering, University of California, Berkeley, California 94720
C.T. Foxon School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom
Kin M. Yu and Wladek Walukiewicza) Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (Received 9 August 2011; accepted 30 September 2011)
Thin films of GaNBi alloys with up to 12.5 at.% Bi were grown on sapphire using low-temperature molecular beam epitaxy. The low growth temperature and incorporation of Bi resulted in a morphology of nanocrystallites embedded in an amorphous matrix. The composition and optical absorption shift were found to depend strongly on the III:V ratio controlled by the Ga flux during growth. Increasing the incorporation of Bi resulted in an increase in conductivity of almost five orders of magnitude to 144 X-cm 1. Holes were determined to be the majority charge carriers indicating that the conductivity most likely results from a GaNBi-related phase. Soft x-ray emission and x-ray absorption spectroscopies were used to probe the modification of the nitrogen partial density of states due to Bi. The valence band edge was found to shift abruptly to the midgap position of GaN, whereas the conduction band edge shifted more gradually. I. INTRODUCTION
Alloying is commonly used to control structural and optoelectronic properties (e.g., bandgap, lattice constant) of compound semiconductors for specific device applications. The most common semiconductor alloys are pseudobinary alloys composed of isoelectronic elements that are relatively well matched in terms of atom size, ionicity, and electronegativity, e.g., SiGe, AlGaAs, GaAsP, etc. In these cases, the alloy properties can be approximated by the extrapolation of the properties of their corresponding binary end compounds (Vegard’s law). However, in the last decade, a new class of semiconductor alloys known as highly mismatched alloys (HMAs), formed by the
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Address all correspondence to this author. e-mail: [email protected] This paper has been selected as an Invited Feature Paper. DOI: 10.1557/jmr.2011.376 J. Mater. Res., Vol. 26, No. 23, Dec 14, 2011
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isoelectronic substitution of elements with very different size and/or electronegativity in the anion sublattice, have attracted interest. In
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