Electronic structure and the local electroneutrality level of SiC polytypes from quasiparticle calculations within the G
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ONIC PROPERTIES OF SOLID
Electronic Structure and the Local Electroneutrality Level of SiC Polytypes from Quasiparticle Calculations within the GW Approximation V. N. Brudnyia,* and A. V. Kosobutskyb a
Tomsk State University, pr. Lenina 36, Tomsk, 634050 Russia *email: [email protected] b Kemerovo State University, ul. Krasnaya 6, Kemerovo, 650043 Russia Received July 13, 2011
Abstract—The most important interband transitions and the local charge neutrality level (CNL) in silicon carbide polytypes 3CSiC and nHSiC (n = 2–8) are calculated using the GW approximation for the self energy of quasiparticles. The calculated values of band gap Eg for various polytypes fall in the range 2.38 eV (3CSiC)–3.33 eV (2HSiC) and are very close to the experimental data (2.42–3.33 eV). The quasiparticle corrections to Eg determined by DFT–LDA calculations (about 1.1 eV) are almost independent of the crystal structure of a polytype. The positions of CNL in various polytypes are found to be almost the same, and the change in CNL correlates weakly with the change in Eg, which increases with the hexagonality of SiC. The calculated value of CNL varies from 1.74 eV in polytype 3CSiC to 1.81 eV in 4HSiC. DOI: 10.1134/S1063776112050019
INTRODUCTION Due to its unique electrical, thermal, and chemi cal properties, silicon carbide is considered as one of the most promising materials for power and high temperature electronics. SiC is also a promising material for producing nuclear radiation detectors owing to its low density and a high threshold energy of radiation defect formation. The effects of various types of highenergy action on the properties of SiC were studied in numerous investigations, most of which were generalized in review [1]. It was found that the radiation of silicon carbide polytypes by var ious types of highenergy radiation increases the electrical resistivities of both n and ptype materials because of the shift in the Fermi level deep into the band gap of a semiconductor. However, the large band gap of silicon carbide (2.4–3.3 eV) hinders an experimental determination of the limiting doze val ues of electrical resistivity ρlim(D) and, correspond ingly, the limiting position of the Fermi level Flim in an irradiated material from direct Hall effect or ther mopower measurements. Nevertheless, it is known that Flim in an irradiated semiconductor is identical to the branch point of the complex band structure (“neutral” point) of a crystal, the position of which in the band spectrum of the semiconductor corresponds to the energy at which the character of defect (gap) states in the crystal changes from donor states (which mainly consist of the valence band states) to acceptor states (which mainly consist of the conduction band states). Since the neutral point corresponds to the
condition of electron–hole equilibrium for a charge bound at gap (defect) states without regard for free charge carriers, it is also called the (local) charge neutrality level (CNL) [2–4]. CNL determines the electronic properties of a d
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