We report on optical spectroscopy (photoluminescence and photoluminescence excitation) on twodimensional self-organized layers of (C6H5C2H4 − N H3)2P bI4 perovskite. Temperature and excitation power dependance of the optical spectra gives a new insight into the excitonic and phononic properties of this hybrid organic/inorganic semiconductor. In particular, exciton-phonon interaction is found to be more than one order of magnitude higher than in GaAs QWs. As a result, photoluminescence emission lines have to be interpreted in the framework of a polaron model. PACS numbers: Valid PACS appear hereOptical properties of soft materials have attracted much attention for years thanks to their potential applications in optoelectronics devices. In particular, these last years, an increasing number of studies are dedicated on hybrid organic-inorganic materials[1], due to the possibility of combining the properties both of inorganic materials (high mobility, electrical pumping, band engineering) and of organic materials (low cost technology, high luminescence quantum yield at room temperature). In this context, organic-inorganic perovkites, having a chemical formula (R − NH3) 2 MX 4 where R is an organic chain, M is a metal and X a halogen, represent a natural hybrid system. Such perovskites present a great flexibility in their optical properties: the spectral position of the excitonic transitions can be tailored by substituting different halides X [2, 3], the photoluminescence efficiency can be tailored by changing the organic part R [4]. This kind of perovskites has been studied both in the framework of fundamental studies [2,3,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24] and of applications in optoelectronic as the active material in a distributed feedback laser for example [25]. Recently the strong coupling regime between the perovskite exciton and the optical mode of a Pérot-Fabry microcavity has been demonstrated at room temperature in the UV range [5] and in the visible range [6,7]. The physical properties of these new polaritons have now to be investigated. In particular, the demonstration of polariton-polariton interactions which lead to polariton scattering would be a breakthrough for the physics of these new devices in the context of the low threshold polariton lasers [26,27,28]. To evaluate these possibilities, a good knowledge of the perovskite material electronic properties is needed. As an example, the energy of the phonons and the strength of the electron-phonon coupling will indicate whether an efficient relaxation of perovskite polaritons is conceivable. Additionally, the origin of the different perosvkite luminescence lines has to be clarified to improve the knowledge about the exciton which couples to the cavity mode. .In this paper, we report on the optical properties of a particular perovskite molecule, namely [bi-(phenethylammonium) tetraiodoplumbate]: (C 6 H 5 C 2 H 4 − N H 3 ) 2 − P bI 4 (named PEPI), absorbing and emitting in the green part of the visible range. Photoluminescence (PL) ...

We have studied the electronic confinement in hexagonal ͑0001͒ GaN / AlN multiple quantum wells by means of structural ͑high-resolution x-ray diffraction and transmission electron microscopy͒ as well as optical characterizations, namely intersubband absorption and interband photoluminescence spectroscopies. Intense intersubband absorptions covering the 1.33-1.91 m wavelength range have been measured on a series of samples with well thicknesses varying from 1 to 2.5 nm. The absorption line shape exhibits either a pure Lorentzian shape or multiple peaks. In the first case the broadening is homogeneous with a state-of-the-art low value of 67 meV. We deduce a dephasing time of the electrons in the excited subband T 2 of about 20 fs. For structured spectra the absorption can be perfectly reproduced with a sum of several Lorentzian curves; the individual peaks originate from absorption in quantum well regions with thickness equal to an integer number of monolayers. We have also carried out simulations of the electronic structure which point out the relevance of the nonparabolicity and many-body corrections on the intersubband absorption energy. The intersubband absorption exhibits a blue shift with doping as a result of many-body effects dominated by the exchange interaction. An excellent agreement with the experimental data is demonstrated. The best fit is achieved using a conduction band offset at the GaN / AlN heterointerfaces of 1.7± 0.05 eV and a polarization discontinuity ⌬P / ͑⑀ 0 ⑀ r ͒ of 10±1 MV/cm.

We report on the controlled growth by molecular beam epitaxy of 20-period Si-doped GaN∕AlN quantum dot (QD) superlattices, in order to tailor their intraband absorption within the 1.3–1.55μm telecommunication spectral range. The QD size can be tuned by modifying the amount of GaN in the QDs, the growth temperature, or the growth interruption time (Ostwald ripening). By adjusting the growth conditions, QDs with height (diameter) within the range of 1–1.5nm (10–40nm), and density between 1011 and 1012cm−2 can be synthesized, fully strained on the AlN pseudosubstrate. To populate the first electronic level, silicon can be incorporated into the QDs without significant perturbation of the QD morphology. All the samples exhibit strong p-polarized intraband absorption at room temperature. The broadening of the absorption peak remains below 150meV and can be as small as ∼80meV. This absorption line is attributed to transition from the s ground level of the QD to the first excited level along the growth axis, pz. The peak energies of both photoluminescence emission and intraband absorption are consistent with the QD structural characteristics, and with their evolution by changing the growth conditions. Tuning of the intraband absorption from 0.740eV (1.68μm)to0.896eV (1.38μm) is demonstrated. Finally, we show that the AlN buffer layer can be replaced by a conductive AlxGa1−xN (x=0.35 and 0.6) ternary alloy without significant modification of the intraband properties of the QD stack.