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S. S. Pan, S. Wang, Y. X. Zhang, Y. Y. Luo, F. Y. Kong, S. C. Xu, J. M. Xu, G. H. Li.
Applied Physics A, November 2012, Volume 109, Issue 2, pp 267-271.
Key Laboratory of Materials Physics, Anhui Key Laboratory of Nanomaterials and Nanostructures, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei, 230031, PR China.
Abstract
p-type nitrogen-doped SnO2 (SnO2:N) films were grown by thermal processing of amorphous tin nitride films at temperatures between 350 and 500 ∘C in flowing O2–Ar gas mixture. From high-resolution X-ray photoelectron spectroscopy (XPS) and X-ray diffraction patterns, it is deduced that the N atoms replace the O atoms in the SnO2 lattice. The N dopant is more tightly bound in SnO2:N at higher thermal oxidation temperatures deduced from the XPS results. The hole concentration obtained at an oxidation temperature of 400 ∘C is 1.87×1019 cm−3, which is dramatically enhanced compared to previous reports. Our results indicate that the high-temperature thermal oxidation of tin nitride is a facile and effective route to alleviate the self-compensation effect, reduce the content of {Gamma}-N2 double donors, and reinforce the stability of N dopant in the SnO2:N films.
Additional Information:
The wide band gap of 3.6 eV (3.37 eV for ZnO, 3.41 eV for GaN), high exciton binding energy of 130 meV (60 meV for ZnO, 21 meV for GaN) and outstanding electrical and optical properties make SnO2 a promising host material for next generation nonpolar ultraviolet (UV) light emitting devices applications. The application of SnO2 as UV light source is obstructed from its dipole-forbidden band structure, the free exciton emission can hardly be observed from bulk SnO2 or films due to the parity selection rule.
In these recent contributions from scientists of the Institute of Solid State Physics, Chinese Academy of Sciences (CAS), P.R. China, they use two strategies to achieve the exciton emission in SnO2 films: (1) Nitrogen doping: the N dopant may change the VB symmetry, and exciton luminescence was observed from N-doped SnO2 films (Ref. Applied Physics Letters 89, 251911 (2006)). (2) SnO2 nanocrystalline films: significant reduction of bulk SnO2 into nanoscale dimensions can modify the confinement of electron wavefunction. The scientists report on strong surface exciton (375 ~364 nm) and free exciton (338 ~ 330 nm) emissions from SnO2 nanocrystalline films. They found the intensities of excitons increase with the decrease of the average crystallite size of the films, and explained the results by proposing a simple physical model. The proposed model presents a general and valuable insight on size effect on luminescence intensity of semiconductor nanocrystals (Ref. (a) Journal of Applied Physics 113, 143104 (2013); (b) Applied Physics Letters 97, 221105 (2010)).
