Enhanced Electrical Properties and Stability of P-Type Conduction in ZnO Transparent Semiconductor Thin Films by Co-Doping Ga and N

Chien-Yie Tsay,Wan-Yu Chiu

doi:10.3390/coatings10111069

Abstract

P-type ZnO transparent semiconductor thin films were prepared on glass substrates by the sol-gel spin-coating process with N doping and Ga–N co-doping. Comparative studies of the microstructural features, optical properties, and electrical characteristics of ZnO, N-doped ZnO (ZnO:N), and Ga–N co-doped ZnO (ZnO:Ga–N) thin films are reported in this paper. Each as-coated sol-gel film was preheated at 300 °C for 10 min in air and then annealed at 500 °C for 1 h in oxygen ambient. X-ray diffraction (XRD) examination confirmed that these ZnO-based thin films had a polycrystalline nature and an entirely wurtzite structure. The incorporation of N and Ga–N into ZnO thin films obviously refined the microstructures, reduced surface roughness, and enhanced the transparency in the visible range. X-ray photoelectron spectroscopy (XPS) analysis confirmed the incorporation of N and Ga–N into the ZnO:N and ZnO:Ga–N thin films, respectively. The room temperature PL spectra exhibited a prominent peak and a broad band, which corresponded to the near-band edge emission and deep-level emission. Hall measurement revealed that the ZnO semiconductor thin films were converted from n-type to p-type after incorporation of N into ZnO nanocrystals, and they had a mean hole concentration of 1.83 × 1015 cm−3 and a mean resistivity of 385.4 Ω·cm. In addition, the Ga–N co-doped ZnO thin film showed good p-type conductivity with a hole concentration approaching 4.0 × 1017 cm−3 and a low resistivity of 5.09 Ω·cm. The Ga–N co-doped thin films showed relatively stable p-type conduction (>three weeks) compared with the N-doped thin films.

Highlights

Wide-bandgap oxide semiconductors have gained considerable attention and received great interest due to their potential for applications in optoelectronic devices, photovoltaic devices, and transparent oxide electronics, such as ultraviolet photodetectors, short wavelength light-emitting diodes, thin-film solar cells, transparent resistive random access memory, and transparent field-effect transistors [1,2,3,4]
Stable p-type ZnO transparent semiconductor thin films have been deposited on alkali-free glass substrates with Ga and N co-doping by the sol-gel spin-coating process
X-ray diffraction (XRD) patterns showed that these sol-gel-derived ZnO-based thin films were polycrystalline with a single hexagonal structure, and the microstructural features were significantly changed by the impurity doping

Summary

Introduction

Wide-bandgap oxide semiconductors have gained considerable attention and received great interest due to their potential for applications in optoelectronic devices, photovoltaic devices, and transparent oxide electronics, such as ultraviolet photodetectors, short wavelength light-emitting diodes, thin-film solar cells, transparent resistive random access memory, and transparent field-effect transistors [1,2,3,4]. The fabrication of light-emitting diodes, p-n junction photodetectors, and complementary metal-oxide-semiconductor devices requires the combination of both n-type and p-type oxide semiconductors. The lack of availability of stable p-type oxide semiconductors limits the electrical efficiency of p-n junction-based devices or bipolar device applications [3,5]. The development of stable and reproducible p-type oxide semiconductor thin films is necessary.

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Results

Conclusion