Electronic and Optical Properties of Substitutional and Interstitial Si-Doped ZnO

Hsuan-Chung Wu,Yen-Chun Peng,Tsu-Ping Shen

doi:10.3390/ma5112088

Abstract

This study investigates the formation energies, electronic structures, and optical properties of pure and Si-doped ZnO using density functional theory and the Hubbard U (DFT + Ud + Up) method. The difference in lattice constants between calculated results and experimental measurements is within 1%, and the calculated band gap of pure ZnO is in excellent agreement with experimental values. This study considers three possible Si-doped ZnO structures including the substitution of Si for Zn (Sis(Zn)), interstitial Si in an octahedron (Sii(oct)), and interstitial Si in a tetrahedron (Sii(tet)). Results show that the formation energy of Sis(Zn) defects is the lowest, indicating that Sis(Zn) defects are formed more easily than Sii(oct) and Sii(tet). All three of the Si defect models exhibited n-type conductive characteristics, and except for the Sii(oct) mode the optical band gap expanded beyond that of pure ZnO. In both the Sii(oct) and Sii(tet) models, a heavier effective mass decreased carrier mobility, and deeper donor states significantly decreased transmittance. Therefore, the existence of interestitial Si atoms was bad for the electric and optical properties of ZnO.

Highlights

Wurtzite zinc oxide (ZnO) is a semiconductor with a wide band gap of 3.37 eV and a large exciton binding energy of 60 meV at room temperature [1]
ZnO has been widely used in photoelectric applications, such as transparent conductive oxides (TCOs) [2], transistors [3], nano-energy-related fields [4], diluted magnetic semiconductors [5], and dye-sensitized solar cells (DSSCs) [6]
The formation energies of three different structures of Si-doped ZnO (Sis(Zn), Sii(oct), and Sii(tet)) were calculated using a 2 × 2 × 2 supercell to determine the possibility and stability of a defect structure

Summary

Introduction

Wurtzite zinc oxide (ZnO) is a semiconductor with a wide band gap of 3.37 eV and a large exciton binding energy of 60 meV at room temperature [1]. Nomoto et al [18] indicated that Si dopant can improve the uniformity of resistivity on the substrate surface of AZO:Si thin films by sputtering deposition. These results imply that Si doping in ZnO has great potential for applications requiring flexible substrates and large area deposition. This study adopts the DFT + Ud + Up (Ud,Zn = 10 eV and Up,O = 7 eV) method to investigate electronic and optical properties of Si-doped ZnO. This study investigates the formation energy, band structures, density of states (DOS), and optical properties of Si-doped ZnO

Calculation Models and Methods

Formation Energy

Band Structure

Density of States

Optical Properties

Conclusions