Role of spontaneous polarization in the formation of NH -SiC/3 C -SiC/ NH -SiC structures based on silicon carbide polyt
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CONDUCTOR STRUCTURES, INTERFACES, AND SURFACES
Role of Spontaneous Polarization in the Formation of NH-SiC/3C-SiC/NH-SiC Structures Based on Silicon Carbide Polytypes S. Yu. Davydova^ and A. V. Troshinb aIoffe
Physicotechnical Institute, Russian Academy of Sciences, ul. Polytechnicheskaya 26, St. Petersburg, 194021 Russia ^e-mail: [email protected] bSt.-Petersburg State Electrotechnical University, ul. Popova 5, St.-Petersburg, 197376 Russia Submitted February 11, 2008; accepted for publication February 13, 2008
Abstract—The effect of the electrostatic field caused by spontaneous polarization in hexagonal plates of a heterostructure based on NH-SiC/3C-SiC/NH-SiC silicon carbide polytypes on relative positions of energy bands is considered. It was shown that the asymmetry arising in the system is associated with the superposition of polarization and contact fields. PACS numbers: 73.20.At, 73.21.Fg, 77.84.Bw DOI: 10.1134/S1063782608110080
1. Recently, interest has grown in the study of the effect of spontaneous polarization Psp on characteristics of heterostructures (HSs) based on cubic and hexagonal silicon carbide polytypes [1]. In the cubic polytype 3C-SiC, all four sp3 orbitals are equivalent; whereas in hexagonal polytypes H-SiC, there is a preferential axis c and the sp3 orbital is extended along this axis, which differs from the other three. As a result, the elementary tetrahedron gains a dipole moment, which causes spontaneous polarization in noncubic polytypes [2, 3]. Thus, noncubic SiC polytypes are pyroelectric materials. In a three-layer HS, such as NH-SiC/3C-SiC/NH-SiC (NH/3C/NH-SiC, N = 2, 4, 6, 8), the electric field induced by spontaneous polarization of NH plates penetrates into the 3C regions and changes the relative positions of bands. At the same time, the HS cubic component also affects the Psp screening. All these factors make it necessary to consider Psp in boundary conditions in calculating the energy-band diagram of this system [4, 5]. The corresponding calculations for such heterojunctions (HJs) as NH-SiC/3C-SiC are given in [6].
cubic interlayer and to analyze the effect of considering spontaneous polarization m the energy diagram of this system. 2. In the three-layer system, left- and right-hand HJs are nonequivalent. First, contact fields Fc of HJs have opposite signs. Here, the contact field is understood as the quantity defined by the relation
The following should also be noted. Piezoelectric polarization arises in the HS due to mismatched lattices of contacting semiconductors. However, the lattice mismatch in silicon carbide polytypes is extremely small; e.g., the distances between nearest neighbors in pure cubic 3C polytype differ from those in the purely hexagonal 2H polytype by ~0.5% [7]. Therefore, for structures based on SiC polytypes, only the role of spontaneous polarization can be considered, with neglect of piezoelectric polarization [1–5]. The goal of this study is to construct a simple model of the three-layer HS based on SiC polytypes with hexagonal plates an
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