Conduction band modifications by d states in vanadium doped CdO

JOURNAL OF ALLOYS AND COMPOUNDS

卷:822

Article

Li, Y. J.^1,2  Yu, K. M.^3,4  Chen, G. B.^5,6  Liu, Chao Ping^3,7  Walukiewicz, W.^1,8 

[1] Lawrence Berkeley Natl Lab, Mat Sci Div, Berkeley, CA 94720 USA

[2] Huizhou Univ, Elect Sci Dept, Huizhou 516007, Peoples R China

[3] City Univ Hong Kong, Dept Phys, Kowloon, Hong Kong, Peoples R China

[4] City Univ Hong Kong, Dept Mat Sci & Engn, Kowloon, Hong Kong, Peoples R China

[5] Huaiyin Normal Univ Jiangsu, Phys Dept, Huaian, Peoples R China

[6] Huaiyin Normal Univ Jiangsu, Jiangsu Key Lab Chem Low Dimens Mat, Huaian, Peoples R China

[7] Shantou Univ, Dept Phys, Coll Sci, Shantou 15063, Guangdong, Peoples R China

[8] Univ Calif Berkeley, Dept Mat Sci & Engn, Berkeley, CA 94720 USA

关键词: Band anticrossing;    Cadmium oxide;    Optical absorption;    Effective mass;    Transparent conductor;   

DOI  :  10.1016/j.jallcom.2019.153567

来源: Elsevier

【 摘 要 】

3d transition metal ions have been shown to act as donors and to introduce highly localized d-levels when incorporated in CdO. In this work, we synthesized CdO thin films doped with a 3d metal V (CVO) with a V mole fraction x up to 0.1 by radio-frequency magnetron sputtering. CVO thin films exhibit a monotonic increase in the electron concentration n with x up to a saturation value of similar to 1.0 x 10(21) cm(-3) at a dopant concentration x > 0.045. In contrast to CdO doped with shallow donors such as In where the electron mobility mu is > 100 cm(2)/V-s even at a high In doping level of >5%, in CVO the mu decreases continuously from similar to 100 to <10 cm(2)/V-s with increasing x. Spectroscopic ellipsometry measurements show a rapid increase in the effective mass in CVO, consistent with the continuous reduction of The electrical and optical properties of CVO are analyzed in terms of the anticrossing interaction of the localized V d-levels with the extended conduction band (CB) states of the host CdO. Such anticrossing interaction splits the CdO CB into two non-parabolic subbands, E+ and E-. The optical absorption edge of CVO with x > 0.045 is consistent with transitions from the valence band to the empty E+ subband while the much reduced mu can be explained by the increase in effective mass due to flattening of the E- sub-band. Such band anticrossing interaction is a common phenomenon for most transition metal dopants with d electrons in metal oxides and can explain the optoelectronic properties of these materials. (C) 2020 Elsevier B.V. All rights reserved.

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