A comparative DFT study of electronic properties of 2H-, 4H- and 6H-SiC(0001) and SiC() clean surfaces: significance of the surface Stark effect

Jakub Sołtys,Jacek Piechota,Stanisław Krukowski,Michał Łopuszyński

doi:10.1088/1367-2630/12/4/043024

Abstract

The electric field, uniform within a slab, emerging due to Fermi level pinning at both sides of the slab, is analyzed using DFT simulations of SiC surface slabs of different thicknesses. It is shown that for thicker slabs the field is nonuniform and this fact is related to the surface state charge. Using the electron density and potential profiles, it is proved that for high-precision simulations it is necessary to take into account a sufficient number of SiC layers. We show that the use of 12 diatomic layers leads to satisfactory results. It is also demonstrated that the change of the opposite side slab termination, both by different types of atoms or by their location, can be used to adjust the electric field within the slab, creating a tool for simulation of surface properties, depending on the doping in the bulk of the semiconductor. Using these simulations, it was found that, depending on the electric field, the energy of the surface states changes in a different way than the energy of the bulk states. This criterion can be used to distinguish Shockley and Tamm surface states. The electronic properties, i.e. energy and type of surface states of the three clean surfaces: 2H-, 4H-, 6H-SiC(0001) and SiC(), are analyzed and compared using field-dependent DFT simulations.

Highlights

Silicon carbide can exist in very large number of polytypes, of which hundreds were already identified [1]
A number of quantum structure based devices, using SiC as building material was developed [3]. These structures are based on the material having its properties, extremely attractive in many applications in electronics [4], that is a wide bandgap semiconductor, having superior electronic properties, displaying high values of several important parameters like breakdown electric field (2.2 · V · cm−1), forward current density, saturated electron drift velocity (2 · cm · s−1 for 4H-SiC and 2.5 · 107 cm · s−1 for 3C-SiC) and room temperature mobility (370 cm2 · V−1 · s−1 and 720 cm2 · V−1 · s−1 for 6H-SiC and 4H-SiC respectively), and high blocking voltage observed in typical MOSFET devices [3]
The band diagram for the Si-surface of 2H polytype is presented. These results indicate that the surface states associated with the Si atoms are moved down with respect to Valence Band Maximum (VBM)

Summary

Introduction

Silicon carbide can exist in very large number of polytypes, of which hundreds were already identified [1]. A number of quantum structure based devices, using SiC as building material was developed [3] These structures are based on the material having its properties, extremely attractive in many applications in electronics [4], that is a wide bandgap semiconductor, having superior electronic properties, displaying high values of several important parameters like breakdown electric field (2.2 · V · cm−1), forward current density (up to 1 kA · cm−2), saturated electron drift velocity (2 · cm · s−1 for 4H-SiC and 2.5 · 107 cm · s−1 for 3C-SiC) and room temperature mobility (370 cm2 · V−1 · s−1 and 720 cm2 · V−1 · s−1 for 6H-SiC and 4H-SiC respectively), and high blocking voltage observed in typical MOSFET devices [3]. The present paper is devoted to study the methodology of thick slab simulations, the role of electric field (Fig. 1) and the influence of stacking sequence on electronic and structural properties of polar SiC(0001) and SiC(0001) surfaces.

Method of calculation

Preparation of surface models

Findings

Summary