PbTiO3/SrTiO3 interface: Energy band alignment and its relation to the limits of Fermi level variation
PbTiO3/SrTiO3 interface: Energy band alignment and its relation to the limits of Fermi level variation
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DOI：
10.1103/physrevb.84.045317
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发表时间：
2011-07-18
影响因子：
3.7
通讯作者：
Klein, Andreas
中科院分区：
文献类型：
--
作者：
Schafranek, Robert;Li, Shunyi;Klein, Andreas
用原位光电子能谱研究了PbTiO3和SrTiO3之间的界面形成。确定了1.1 +/- 0.1 eV的价带偏置，对应于1.3 +/- 0.1 eV的导带偏置。这些值与SrTiO3和PbTiO3表面的电离势估计的带偏移值很好地一致。与SrTiO3与相同电极材料接触时的势垒高度相比，PbTiO3与不同电极材料接触时的势垒高度相差1.1 eV。结果表明，费米能级钉住对带对准的影响不大，势垒高度是可传递的。在不同条件下在不同衬底上制备的许多薄膜，当它们按照实验确定的带偏移量排列时，观察到的费米能级变化的极限对于两种材料是相同的。通过进一步比较SrTiO3和PbTiO3的电导率，表明这些材料中大部分的费米能级位置范围与观察到的电导率范围相对应，与不同接触材料界面处的费米能级位置范围相当。特别是SrTiO3的电子注入势垒高度可能较低，这与施主掺杂或还原的SrTiO3的金属导电性是一致的，而PbTiO3的势垒高度接近1 eV，这与即使在高掺杂浓度下的高电阻率是一致的。因此，界面处势垒高度的变化提供了任何材料（包括绝缘材料）内部可能的费米能级位置范围，这与理解缺陷特性有关。
The interface formation between PbTiO3 and SrTiO3 has been studied by in situ photoelectron spectroscopy. A valence band offset of 1.1 +/- 0.1 eV, corresponding to a conduction band offset of 1.3 +/- 0.1 eV, is determined. These values are in good agreement with the band offsets estimated from measured ionization potentials of SrTiO3 and PbTiO3 surfaces. The observed band offsets are also in line with a similar to 1.1 eV difference in barrier heights of PbTiO3 in contact with different electrode materials as compared to barrier heights of SrTiO3 with the same electrode materials. The results indicate that the band alignment is not strongly affected by Fermi level pinning and that the barrier heights are transitive. The limits of Fermi level variation observed from a number of thin films prepared on different substrates with different conditions are the same for both materials when these are aligned following the experimentally determined band offsets. By further comparing electrical conductivities reported for SrTiO3 and PbTiO3, it is suggested that the range of Fermi level position in the bulk of these materials, which corresponds to the range of observed conductivities, is comparable to the range of Fermi level position at interfaces with different contact materials. In particular the possibly low barrier height for electron injection into SrTiO3 is consistent with the metallic conduction of donor doped or reduced SrTiO3, while barrier heights similar to 1 eV for PbTiO3 are consistent with the high resistivity even at high doping concentrations. The variation of barrier heights at interfaces therefore provides access to the range of possible Fermi level positions in the interior of any, including insulating, materials, which is relevant for understanding defect properties.