Photonics plus Spintronics

First came solid-state electronics, producing the field effect transistor (FET), in which a tiny voltage applied to a gate enables a much larger current to flow through a circuit. Next came optoelectronics, producing the light emitting diode (LED), in which electrons and holes (the spaces vacated by electrons) are made to combine and produce useful light (unfortunately this does not include silicon, an infamous non-light-emitter, at least until recently). Then came spintronics, producing circuit elements such as magnetoresistive sensors, in which an electron polarization (the direction of an electron's magnetic moment) is an important variable. Now scientists would like to combine optical and magnetic features in a single technology.

Some steps have already been taken: dilute magnet semiconductors (DMS), materials doped with magnetic metal atoms, can be made ferromagnetic; that is, they can be magnetized and will stay magnetic providing you stay below the curie temperature (which is to magnets what the transition temperature is to superconductors). Furthermore, polarized electrons have been used to make polarized photons in the dilute magnet materials.

The latest advance is to make a silicon-compatible spintronics material that functions at room temperature. Arthur Hebard (afh@phys.ufl.edu, 352-392-8842) and his colleagues at the University of Florida show that the semiconductor gallium phosphide (GaP) doped with manganese becomes and stays magnetic above room temperature.

These results suggest that the related compounds, InGaP and AlInGaP, which are already used in light emitting diode applications, might also become magnetic when doped with Mn and thus be useful as polarized light emitters. This should lead handily to spin-LEDs and spin-FETs (requiring much small operating voltages than conventional FETs).

More promising still is possibility of integrating doped-Ga-P spin-FETs and LEDs with silicon technology, the reigning industry standard material. Finally, it should be noted that a result like this, involving the fine tailoring of a material with dopant elements, necessitated a strong collaboration between the physics department at Florida (Hebard) and the department of materials science and engineering (Cammy Abernathy and Steve Pearton) (Theodoropoulou et al., Physical Review Letters, 2 Sept.)