We report electrical spin injection from a ferromagnetic metal contact into a semiconductor light emitting diode structure with an injection efficiency of 30% which persists to room temperature.The Schottky barrier formed at the Fe/AlGaAs interface provides a natural tunnel barrier for injection of spin polarized electrons under reverse bias. These carriers radiatively recombine, emitting circularly polarized light, and the quantum selection rules relating the optical and carrier spin polarizations provide a quantitative, model-independent measure of injection efficiency.This demonstrates that spin injecting contacts can be formed using a widely employed contact methodology, providing a ready pathway for the integration of spin transport into semiconductor processing technology.Revised for Applied Physics Letters 12/17/01

Lead halide perovskites (CH3NH3PbX3, where X = I, Br) and other metal halide complexes (MXn, where M = Pb, Cd, In, Zn, Fe, Bi, Sb) have been studied as inorganic capping ligands for colloidal nanocrystals. We present the methodology for the surface functionalization via ligand-exchange reactions and the effect on the optical properties of IV–VI, II–VI, and III–V semiconductor nanocrystals. In particular, we show that the Lewis acid–base properties of the solvents, in addition to the solvent dielectric constant, must be properly adjusted for successful ligand exchange and colloidal stability. High luminescence quantum efficiencies of 20–30% for near-infrared emitting CH3NH3PbI3-functionalized PbS nanocrystals and 50–65% for red-emitting CH3NH3CdBr3- and (NH4)2ZnCl4-capped CdSe/CdS nanocrystals point to highly efficient electronic passivation of the nanocrystal surface.

Electron spin polarizations of 32% are obtained in a GaAs quantum well via electrical injection through a reverse-biased Fe/AlGaAs Schottky contact. An analysis of the transport data using the Rowell criteria demonstrates that single step tunneling is the dominant transport mechanism. The current-voltage data show a clear zero-bias anomaly and phonon signatures corresponding to the GaAs-like and AlAs-like longitudinal-optical phonon modes of the AlGaAs barrier, providing further evidence for tunneling. These results provide experimental confirmation of several theoretical analyses indicating that tunneling enables significant spin injection from a metal into a semiconductor.

The efficient harvesting of hot carrier energy in semiconductors is typically inhibited by their ultrafast thermalization process. Recently, highly promising experiments reported on the slowdown of the intraband relaxation in hybrid metal halide perovskites. In this work, we report on the presence of long-lived hot carriers in weakly confined colloidal nanocrystals (NCs) of formamidinium lead iodide perovskite (FAPbI3). The effect is apparent from the excitation-dependent lengthening of the rise time and broadening of the high-energy tail of the transient absorption bleaching signal, yielding a retardation of the carrier relaxation by 2 orders of magnitude compared to typical time scales in colloidal semiconductor NCs. Three distinct cooling stages are observed, occurring at sub-picosecond, ∼5 ps, and ∼40 ps time scales, which we attribute to scattering from LO-phonons, contribution from a hot phonon bottleneck effect and Auger heating, respectively. Thermalization appears also influenced by the FAPbI3 NCs purity, with trapping at unreacted precursor impurities further reducing the carrier energy loss rate.

Good progress has recently been made in the development and commercialization of semiconductor light-emitting devices that operate in the visible part of the electromagnetic spectrum, mainly due to the rapidly growing demand for displays, solid-state lighting, and related applications. Of particular significance are the developments in gallium nitride and organic semiconductor technologies. [1][2][3] Epitaxially grown GaN-based inorganic semiconductor structures have found application as efficient, robust, short-wavelength-visible-and UV-light sources. Organic semiconductor light-emitting diodes (LEDs) in turn can span the entire visible spectrum and have low-cost potential due to high-throughput manufacturing, opening attractive prospects for displays and lighting. These two semiconductor families have their own especial advantages and disadvantages. Most notably, GaN structures offer excellent electrical properties but are inherently prone to the complex and expensive fabrication techniques that characterize inorganic semiconductors. Their spectral coverage is also limited, although down-conversion with phosphors allows access to other colors and white-light emission. On the other hand, organic semiconductors offer excellent luminescence properties, with a greater variety of emission wavelengths and significantly higher photoluminescence efficiencies, but exhibit less good electrical behavior. Combining the best attributes of each family would clearly be an attractive proposition.We have previously reported the use of fluorene-based polymer semiconductor films as efficient InGaN wavelengthconversion media, using radiative coupling (absorption/reemission): photons emitted by the InGaN LEDs are absorbed in the polyfluorene film and subsequently re-emitted at longer wavelengths.[4] Here we report a hybrid inorganic/organic semiconductor structure, again employing a polyfluorene thin film, but now with the opportunity to place it in sufficiently close proximity to an underlying InGaN quantum well (QW) that the prospect of highly efficient non-radiative Förster resonant energy transfer (FRET) exists. [5,6] As a consequence, this architecture has the potential to take advantage of the complementary attributes of the two classes of semiconductor that it contains and, thus, might lead to high-performance devices with very desirable electrical and optical characteristics. A schematic of our structures is shown in Figure 1a. The UVlight-emitting InGaN QW (∼ 2 nm thick) is spaced from the blue-light-emitting poly(9,9-dioctylfluorene-co-9,9-di(4-methoxy)phenylfluorene) (F8DP) film (∼ 5 nm thick) by GaN cap layers of variable thickness. Such FRET-based inorganic/organic semiconductor structures have recently been predicted to be theoretically feasible, due to the significantly shorter timescale of the Förster-transfer process relative to direct recombination in the inorganic donor. [7] To date, however, there has not been an experimental demonstration of such a structure. Indeed, the energy-transfer scheme proposed here has...