Photoluminescence and acceptor level state of p -type nitrogen-doped MgZnO films
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B. Yao,a) X.H. Wang, Z.Z. Zhang, Y.M. Lu, D.Z. Shen, B.H. Li, J.Y. Zhang, D.X. Zhao, and X.W. Fan Key Laboratory of Excited State Processes, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China
Z.K. Tang Department of Physics, Hong Kong University of Science & Technology, Clear Water Bay, Kowloon, Hong Kong, China (Received 3 April 2007; accepted 1 June 2007)
A wurtzite nitrogen-doped MgZnO (MgZnO:N) film was grown by plasma-assisted molecular-beam epitaxy (PAMBE) on c-plane sapphire using radical NO as oxygen source and nitrogen dopant. The as-grown film shows n-type conduction at room temperature, but transforms into p-type conduction after annealed. Photoluminescence (PL) spectrum measured at 80 K is dominated by neutral donor-bound exciton emission (D0X) located at 3.522 eV for the n-type MgZnO:N film, but by neutral acceptor-bound exciton emission (A0X) located at 3.515 eV for the p-type MgZnO:N film. By fitting exciton emission intensity of temperature-dependent PL spectra, the binding energies of the D0X and A0X were estimated to be 32 and 43 meV, respectively. Based on the energy shift of exciton emission, the band gap of the MgZnO:N film is estimated to be 3.613 eV, which is 179 meV larger than that of ZnO. Using the Haynes rule, the acceptor energy level of the MgZnO:N film was evaluated to be about 176 meV above the valence band.
I. INTRODUCTION
Owing to a wide band gap of 3.37 eV and large exciton binding energy of 60 meV at room temperature, ZnO is considered to be a candidate material for preparation of short wavelength optoelectronic devices, such as lightemitting diode (LED) and laser diode (LD), etc.1,2 In the recent years, investigations on p-type ZnO and ZnObased LED made a great progress. The p-type ZnO LEDs were prepared by single doping of I or V group elements, such as, Li, N, and P, etc., and codoping of III–V groups, such as Al–N, etc.3−6 Electroluminescence (EL) of ZnO p-n homojunction LEDs was also realized recently7–9; however, the EL wavelengths are not in ultraviolet (UV) range but a blue or yellow light range. To obtain strong near-band-edge UV emission and even high-efficiency UV laser, it is necessary to fabricate LED and LD with
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0349 J. Mater. Res., Vol. 22, No. 10, Oct 2007
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active layers composed of ZnO-based superlattices and quantum wells, which need not only fabricate highquality p-type ZnO, but also develop ZnO alloys barrier materials with band gaps larger than that of ZnO. Since band gap of MgxZn1−xO alloy with wurtzite structure is larger than that of ZnO and can be tuned by changing of Mg concentration,10,11 MgxZn1−xO alloy is proposed to be used as candidate barrier material for fabrication of ZnO-based quantum wells or superlattices. In the recent years, much research was carried out on MgxZn1−xO alloy, and n-type MgxZn1−xO alloy has been produced; ho
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