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

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.

Investigation of the Effects of Rapid Thermal Annealing on the Electron Transport Mechanism in Nitrogen-Doped ZnO Thin Films Grown by RF Magnetron Sputtering

“…It was found that for the as-deposited ZnO:N films, the bandgap energy value was 3.25 ± 0.025 eV, while for the 400 °C and 550 °C RTA samples there was a slight reduction toward 3.20 ± 0.025 eV. These optical bandgap energy values are in good agreement with the literature reports [ 17 , 19 , 27 , 28 ]…”

“…However, to prepare a stable p-type ZnO film by N doping is rather difficult due to the low solubility of nitrogen, and thus the low concentration of holes in the films. Another obstacle to effective p-type doping via the replacement of O by N in the anion sublattice is the simultaneous generation of shallow and deep donor-type defects in the ZnO energy gap, such as oxygen vacancies in the O sublattice, V O , and zinc interstitials, Zn i [ 17 , 18 , 19 ], which leads to self-compensation of N acceptors in ZnO [ 20 ]. Difficulties in the preparation of p-type ZnO films have provoked interest in the studies of ZnO heterojunctions, mainly ZnO–Si heterojunctions.…”

Charge properties and currents in the silicon/nanoparticles of zinc oxide heterostructure irradiated by the solar light

“…At the same time, attention is now focused on obtaining and studying the properties of the ptype zinc oxide. Obtaining the p-type conductivity is complicated by the presence of natural oxygen vacancies, which act as donor states [4]. Today the following elements are acceptors for ZnO: Zn vacancies; IA group: Li, Na, K; IB group: Cu, Ag, Au; VA group: N, P, As, Sb [5].…”

Rectifying ZnO–Na/ZnO–Al aerogels p-n homojunctions

“…A variety of different shaped nanostructures, such as nanorods, nanotubes, nanoneedles, nanowires, nanoflowers, nanospheres [27], plates [28], tetrapods [29], among others, can be deposited in different types of substrates to obtain ZnO films and layered junctions. Many deposition techniques can be used to develop ZnO thin films, including pulsed laser deposition [30], spray pyrolysis [7,31], sol-gel [32,33], RF sputtering [34] and chemical vapor deposition [35]. Among the deposition techniques, the sol-gel process stands out as a bottom-up approach for the production of electronic devices due to its controllable reaction conditions and low process temperatures, that allows the incorporation of organic and inorganic materials [36].…”