Optoelectronic properties of low-dimensional ruddlesden-popper and sillÉn-aurivillius perovskites

Abstract

The versatile corner-sharing octahedral structure and highly tunable chemistry of perovskite-structured crystals endow them a plethora of physical properties. In this work the epitaxy and optoelectronics properties of three optoelectronic perovskites, CH3NH3PbI3, 2D Ruddlesden-Popper phase (C4H9NH3)2PbI4 and quasi-2D Sillén-Aurivillius phase Bi4NbO8Cl, are investigated. Ambiguities on the carrier recombination lifetime of CH3NH3PbI3 were revolved by time-resolved photoluminescence spectroscopy of CH3NH3PbI3 single crystals. It was found that the carrier decay profile yielded two components, the faster component turned out insensitive to excitation intensity and was attributed to the radiative recombination near surface that was dominated by defect-assisted non-radiative processes, while the slower component was inversely proportional to excitation intensity and was attributed to recombination in the bulk. The first van der Waals epitaxy in 2D halide perovskite was developed in Ruddlesden–Popper phase (C4H9NH3)2PbI4 on Si (001) or muscovite mica using cold-wall CVD. Using the single-crystalline epitaxial flakes with lateral size 5~30 μm and thickness 20~200 nm, it was demonstrated that the weak van der Waals interaction from epitaxy and within the crystal can counter-intuitively influence the structural phase transition and electron-phonon coupling. Using temperature-dependent photoluminescence spectroscopy, the remote phononic effect from van der Waals force from substrate was found to reduce structural phase transition temperature by over 150 K, with flake thickness reducing below 100 nm the strength of electron-phonon coupling via Fröhlich interaction was found to reduce by up to 30%. Both discoveries indicate that the conventional understanding on the localized and weak nature of van der Waals forces must be adjusted. The electric-field non-volatile control over spin texture was demonstrated for the first time using ferroelectric Sillén-Aurivillius phase Bi4NbO8Cl. The electric-field control of spin degree of freedom has wide applications in spintronics. The state-of-the-art magnetoelectric technologies mainly relies on multiferroic heterostructures or current-driven spin-charge inter-conversion that are somewhat limited by the volatility, complexity in device fabrication or the high energy consumption of current-based operation. In principle, the spin structure of strong spin-orbital-coupling ferroelectrics is locked with electric dipole ordering and can be switched by switching the ferroelectric orientation (Rashba-Dresselhaus effect). Due to the scarcity of strong spin-orbital-coupling and low-in-defect materials, the experimental demonstration of this concept has so far remained elusive. Using single crystalline Bi4NbO8Cl nanosheets with lateral size 10~30 μm and thickness 100~300 nm and resorting to circular photogalvanic effect, it was found that the response to left/right circularly polarized light was created, erased and recreated by electric poling or sweeping, indicating a direct correlation between ferroelectric orientation and spin selectivity (valley-photon locking). The first demonstration of ferroelectric-field control over spin texture and valley-photon interaction in Bi4NbO8Cl provides a new solution to non-volatile low-power-consumption opto-spintronics.