Publication date: 1st July 2014
Quantum and dielectric confinements are known to induce dramatic changes of physical properties. For conventional semiconductors, modelling and understanding of quantum confinement are well developed, while significant dielectric confinement rarely occurs. Moreover, models developed to investigate dielectric confinement are often limited to abrupt interfaces. In this work, both these effects are investigated in layered Hybrid Organic Perovskites (HOP) [1-3]. First, concepts of effective mass and quantum well are carefully analyzed [4]. For ultrathin layers, the effective mass model [5] fails to understand quantitatively the quantum confinement effect [4]. Our findings suggest that absence of superlattice coupling and importance of non-parabolicity effects prevents the use of simple empirical models based on effective masses and envelope function approximations. We present an alternative approach where 2D HOP are treated as composite materials and introduce a first principles based procedure to calculate band offsets. This is the first quantitative evaluation of the type-I quantum well concept introduced for such hybrids by Mitzi [2]. Next, we introduce a new method to investigate dielectric confinement in 2D HOP [1,6], beyond the standard approximation based on dielectric constant profiles with abrupt interfaces. We show that dielectric self-energy profiles significantly contribute to the confinement of both monoelectronic and excitonic states. These approaches may be extended to 3D HOP-based heterostructures and are relevant for other classes of layered materials. Noteworthy, dielectric effects are also crucial in 3D HOP. In fact, screening of the exciton by collective rotations of organic cations has recently been suggested [7].
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[3] J. Even, et al, Phys. Rev. B. 86, 205301 (2012), L. Pedesseau, et al, Optical and Quantum Electronics, 2013, 1-8, DOI: 10.1007/s11082-013-9823-9
[4] J. Even, L. Pedesseau, C. Katan, submitted
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[7] J. Even, et al, J. Phys. Chem. C., 2014 118, 11566.
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