spin Electronics: Optical Studies of Spin Injection in Semiconductor/Semiconductor and Metal/Semiconductor Heterostructures

This proposal was received in response to the Spin Electronics for the 21st century Initiative, Program solicitation NSF 02-036. The proposal focuses on the study of spin injection phenomena in a variety of spin Light Emitting Diodes (spin-LEDs). The proposed work has an experimental as well as a theoretical component. All the devices that will be used in the experimental part of this proposal have an AlGaAs(n)/GaAs/AlGAs(p) light emitting diode at their core. The circular polarization of the diode emission is used to determine the relative spin population of carriers confined in the GaAs layer. In ZnMnSe based spin-LEDs the ZnMnSe contact layer is the source of spin polarized electrons. In this well studied system we will explore the effects of resonant heating of the electrons and holes at various components of the device using far infrared (FIR) monochromatic light. Choice of FIR wavelength and of the externally applied magnetic field allows the study of the effects of heating on the diode output of a particular carrier (electron or hole) in a specific component of the device (GaAs, AlGaAs or ZnMnSe layer) . In addition we will be using specially designed, n-type modulation doped ZnMnSe spin LEDs to study the population statistics of electrons confined in the GaAs quantum well of each diode and occupying a number of Landau levels. The second type of spin-LED will use a ferromagnetic layer as spin polarized electron source with the easy magnetization axis perpendicular to the layer axis. Such a device is expected to require only a few hundred Gauss to operate, as opposed to a few tesla required by the recently developed Fe-based spin LEDs in which the easy magnetization axis lies in the Fe layer plane. Finally we plan to explore AlGaMnAs as a potential spin polarized hole injector. In the theoretical component of this proposal we describe investigations of several important phenomena that take place in spin injection LEDs and affect the operation and efficiency of these devices. We propose to investigate the capture process of the carrier in the GaAs wells and the subsequent energy relaxation to the lowest confinement subbands e1 and h1. The role of phonon emission and the associated spin-flip processes will be explored. A very close and synergistic relationship between the experimental and the theoretical components of the proposed work is expected to contribute to the success of the project. An educational aspect of the proposed work will involve two undergraduate students in the program (from Physics and/or EE) working closely with graduate students and the co-investigators. Support for the undergraduate students will be requested from the REU program