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A scalable method for controlled synthesis of luminescent compound semiconductor nanocrystals (quantum dots) using microemulsion-gas contacting at room temperature is reported. The technique exploits the dispersed phase of a microemulsion to form numerous identical nanoreactors. ZnSe quantum dots were synthesized by reacting hydrogen selenide gas with diethylzinc dissolved in the heptane nanodroplets of a microemulsion formed by self-assembly of a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) amphiphilic block copolymer in formamide. A single nanocrystal is grown in each nanodroplet, thus allowing good control of particle size by manipulation of the initial diethylzinc concentration in the heptane. The ZnSe nanocrystals exhibit size-dependent luminescence and excellent photostability. 20 3 550 553 Cited By :74

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., Comment: 4 pages, 4 figures, submitted to APL

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., Comment: 14 pages including 3 figures, version accepted by Applied Physics Letters - A. Hanbicki, et al. Appl. Phys. Lett. 80 (7), p.TBD (2002)

The spin-polarized light-emitting diode (spin-LED) is a very effective tool for accurately quantifying electrical spin injection in a model independent manner. We resolve and identify various components which occur in the electroluminescence (EL) spectra of GaAs quantum-well-based spin-LEDs, and examine the circular polarization of each. While a number of components exhibit significant circular polarization, the values do not necessarily reflect the electrical spin injection efficiency. We show that a reliable measure of spin injection efficiency can be obtained only if one takes care to spectroscopically resolve and accurately identify the free exciton or free carrier components of the EL spectrum, and exclude other components. © 2001 American Institute of Physics. 79 19 3098 3100 Cited By :62

The electroluminescence (EL) spectra from $\mathrm{Fe}∕\mathrm{Al}\mathrm{Ga}\mathrm{As}(n)∕\mathrm{Ga}\mathrm{As}∕\mathrm{Al}\mathrm{Ga}\mathrm{As}(p)$ spin LEDs contain an ${e}_{1}{h}_{1}$ excitonic feature; in addition, they exhibit new features not present in the photoluminescence (PL) spectra, that are ``satellites'' or ``replicas'' of the exciton. These satellites are red shifted with respect to ${e}_{1}{h}_{1}$ by energies that are approximately equal to those of zone edge phonons in GaAs. The intensity of the replicas depends strongly on bias voltage. In the presence of a magnetic field the satellites become circularly polarized as ${\ensuremath{\sigma}}_{+}$ but their polarization is always lower than that of ${e}_{1}{h}_{1}$. The satellites are interpreted as due to recombination processes that involve zone edge electrons that tunnel into the GaAs quantum well. These processes occur simultaneously with the emission of zone-edge phonons. Our interpretation is supported by a numerical simulation of the properties of electrons tunneling through an $\mathrm{Fe}∕\mathrm{Ga}\mathrm{As}(n)$ Schottky barrier.

A study was performed on a Schottky tunnel barrier contact for electrical spin injection from a magnetic metal into a semiconductor. It was reported that spin injection from a Fe Schottky contact produced a spin polarization of 32% in an AlGaAs/GaAs quantum well. The atomic structure of the spin injecting interface was examined with transmission electron microscopy (TEM). Sponsors: Magnetics Society of the IEEE Conference code: 61560

The electrical spin injection and band offsets in an n-type ferromagnetic semiconductor heterostructure were discussed. The electrical spin injection from spin-LED structures showed defect-dominated electroluminescence. The analysis showed that the addition of a ZnSe interlayer provides a smaller conduction band offset in CdCr2Se4/ZnSe/(AlGa)As heterostructure. Sponsors: Magnetics Society of the IEEE Conference code: 61560

Electrical spin injection and band offsets in an n-type ferromagnetic semiconductor heterostructure of CdCr2Se4-AlGaAs-GaAs are studied. Epitaxially grown CdCr2Se4 films exhibit hysteresis behavior with significant remanence, an in- plane easy axis with a coercive field of 125 Oe. The cross section of the LED and the band alignment were shown. © 2003 IEEE. Sponsors: Magnetics Society of the Institute of Electrical and Electronics Engineers Conference code: 114081

A report on the electrical spin injection from a magnetic Schottky tunnel contact into a semiconductor was presented. The temperature dependence of the optical polarization and corresponding spin injection efficiency was shown. The results demonstrated that spin injecting contacts was formed using a widely employed contact methodology. Sponsors: IEEE Conference code: 60350

The effects of the interface microstructure on spin-injection efficiency in Zn1-xMnxSe/AlyGa1-yAs-GaAs spin-polarized light-emitting diodes (spin-LEDs) were studied. It was shown that the quantum well (QW) spin polarization correlates inversely with the density of linear defects resulting from stacking faults at the ZnMnSe/AlGaAs interface. 89 16 166602/1 166602/4 Cited By :87

We have fabricated spin-polarized light-emitting diode structures via epitaxial regrowth of Znl-xMnxSe on air-exposed surfaces of AlyGal-yAs/GaAs quantum wells. No passivation procedures were used to protect or prepare the III-V surface. The electroluminescence is strongly circularly polarized due to the electrical injection of spin-polarized electrons from the ZnMnSe contact into the GaAs quantum well. An analysis of the optical polarization yields a lower hound of 65% for the spin injection efficiency. These results demonstrate the robustness of the spin injection process in the diffusive transport regime, and attest to the practicality of manufacturing semiconductor-based spin injection devices. © 2000 American Institute of Physics. 77 24 3989 3991 Cited By :58

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.