期刊
PHYSICAL REVIEW B
卷 79, 期 19, 页码 -出版社
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevB.79.195105
关键词
aluminium; band structure; Brillouin zones; conduction bands; density functional theory; electron density; energy gap; Fermi level; gallium; indium; photoelectron spectra; renormalisation; semiconductor thin films; valence bands; zinc compounds
资金
- Spanish Government MEC [MAT2005-07908-C02-01, FIS2006-12117-C04-01, MAT2008-06873-C02-02]
- Consolider Program [CSD2007-00041, CSD2007-00045]
- Generalitat Valenciana [GV06/151]
- Generalitat de Catalunya [2005 SGR 683]
- 6th European Community Framework Program [MEIF-CT2006- 024542]
Chemical effects on the conduction-band filling and band-gap renormalization in ZnO thin films doped with group-III elements (Al, Ga, and In) are investigated by means of optical and photoemission experiments and first-principles density-functional calculations. The Fermi-level position, as obtained from ultraviolet photoemission measurements, exhibits a relatively small and positive shift (about 0.4 eV) with respect to the valence band for increasing electron concentrations up to 10(21) cm(-3). The optical gap exhibits a much larger increase for the same concentration range and the total shift appears to be smaller for In-doped ZnO. Absorption measurements under pressure show that the pressure coefficient of the optical gap is correlated with the electron concentration in films, decreasing with increasing electron concentration. As a consequence, the contributions of band filling and band-gap renormalization to the optical-gap shift can be separated on the basis of the different pressure behavior of the physical parameters involved in each effect. Standard models on band-gap narrowing fail to give account of these results. Supercell density-functional calculations show that the conduction band of heavily doped ZnO is modified by the presence of group-III doping elements, which give rise to small gaps in specific points of the Brillouin zone, modifying the conduction band dispersion in the way predicted, in a much simpler approach, by the band-anticrossing model.
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