# Presentation: 202726

## Novel Optical Investigations of Spin Dependent 

- InAs:Be

- AlAs0.15Sb:Be

**InAs**

- CdMnSe:I(1.5% Mn)

- (University of  Würzburg, Germany)

- Injection of spin-polarized carriers into non-magnetic semiconductors is a prerequisite to the success of the emerging field of semiconductor **spintronics**, where *spin* transport and manipulation replace and/or augment the charge transport and manipulation of conventional electronic devices. Spin-injection into narrow-gap-semiconductors, such as InAs, is important due to the large coupling of spin and orbital degrees of freedom, which give rise to a variety of spin manipulation schemes. We have shown for the first time spin-injection into InAs measured by an optical technique that probes the circular polarization characteristics of recombination emission from a LED-type structure. We observe a *positive* polarization degree *P*l for a structure with a spin-aligner and a *negative P*l for un-polarized injection. This is consistent with calculations based on a rate-equation model that includes finite spin and recombination life-times and the complex band structure of InAs. (work also supported by DARPA/ONR and NSF-ECS 0224225).

**Spin-LEDs are pro-cessed into mesas (top-emission)**

**Band diagram of spin-LEDs. Spins are polarized in an applied magnetic field by passing through a material with large spin-splitting (CdMnSe) and recombine in InAs with unpolarized holes**.

- Experimental results (squares) and model calcu-lations (lines) for equal spin-flip and recombination times for unpolarized (blue) and polarized (red) injection.

**Novel Optical Investigations of Spin Dependent **
**Effects in Semiconductor Nanostructures **

**Notes:**
We are rapidly approaching the end of several decades of rapid increases in computer processing capacity (doubling every three years) that have produced remarkable economic growth and have pervasively impacted our society. Fundamental physical limits associated with shrinking the size of digital logic circuits dictate the end of this continued growth within the next 20 years.  These conventional digital computers and processing technologies, which have fueled our information economy, make use of moving the electron charge in integrated circuits to represent the “zeros” and “ones”  (the computer bits) and to perform digital computation. Entirely new approaches are needed for future generations of information technology to continue the remarkable growth seen over the past several decades.  Quantum Computing and Quantum Information Processing represent one such paradigm.  Quantum logic uses the infinite number of combinations of states of a two-level system that are allowed by quantum mechanics as the basis of quantum bits or “qubits’; this can lead to great improvements in certain types of computing and in encryption for secure communications.  The electron spin, another fundamental property of the electron, is an ideal two-level system and is thus a natural quantum bit; as such it plays a central role in many approaches to quantum computing.  The electron spin also provides additional functionality in more conventional spin-based logic circuits (“spintronics’). Recent work in Japan has shown that a factor of five increase in processing speed may be possible with the use of “spin transistor” logic elements. Injection of spin-polarized electrons into the narrow-gap semiconductor, InAs, is important due to the advantages of this material for use in spin transistors.  The results  described above show for the first time that a significant spin polarization can be injected into InAs and measured by optical techniques.

## Novel Optical Investigations of Spin Dependent 

**Effects in Semiconductor Nanostructures **

- B. D. McCombe, University at Buffalo; DMR 0203560

**Education**

**Broader Impact**

- Three graduate students and one undergraduate student have been involved in this work.  One Ph.D. student finished in August of this year. He already has several groups in the US and in Europe interested in hiring him for a post-doctoral position. Since 2002, the PI has given two general interest public lectures and one lecture to the Western New York Physics Teachers Association, entitled “What in the world is Spintronics?”, in an effort to demystify this emerging technology and make it understandable to the general public and to high school teachers, and, subsequently, to high school students.

- New paradigms are needed for future generations of information technology to maintain the remarkable growth of the past several decades, has so pervasively impacted our society.  _Spintronics_ is one possible new paradigm, and the electron spin (rather than its charge) is receiving much attention as an another intrinsic property of the electron that can be used for new/improved functionalities in semi-conductor devices. Spin-injection into a narrow-gap material is an essential requirement for the success of this new technology, as these materials provide strong intrinsic mechanisms that permit spin manipulation in “spintronic” device structures.