Research in the Petrou group during the last ten years has concentrated on the emerging field of spintronics. In particular, the group studies injection of spin-polarized carriers into semiconductor heterostructures. The devices for this work are provided by Dr. H. Luo (University at Buffalo), Dr. B.T. Jonker (Naval Research Lab), and Dr. S. Holmes (Toshiba-UK). Various techniques such as photoluminescence, electroluminescence, optical pumping, and Hanle spectroscopies are employed. The experiments are carried out in the 5- 300K temperature range in the presence of magnetic fields.

The emphasis of this research is on devices known as "spin-LEDs". These are light emitting diodes which incorporate a magnetic contact that injects spin-polarized electrons into a p-i-n junction. Unpolarized holes are injected from the substrate. Electron and hold pairs recombine at the active site of the device emitting a photon. The recombination takes place either in a quantum well or in a layer of self-assembled quantum dots (QD). The degree of circular polarization of the emitted light is used to determine the spin polarization of the injected electrons.

The purpose of this work is two-fold. The first objective is to optimize spin-LEDs as a method of practical and accurate measurement of the degree of spin polarization of the injected carriers. Several spin-LEDs have been explored as part of this effort. These include devices that utilize ZnMnSe, Fe, and CdCrSe magnetic contacts.

The second objective is to use the spin-LEDs as research tools to investigate the spin-dependent properties of particular nanostructures. For example, spin-LEDs that incorporate a layer of InAs QDs have been used to study the effect of spin imbalance in the QDs generated by the injected spin polarized electrons. This particular work is being carried out with theoretical support by Dr. P. Hawrylak and his co-workers (NRC-Canada).