Researchers Control the Spin of Semiconductor Quantum Dot Shell States

Feb 05, 2009
This is an atomic force microscope image of the uncovered QDs. Credit: Naval Research Laboratory

Scientists at the Naval Research Laboratory (NRL) have recently demonstrated the ability to control the spin population of the individual quantum shell states of self-assembled indium arsenide (InAs) quantum dots (QDs). These results are significant in the understanding of QD behavior and scientists' ability to utilize QDs in active devices or for information processing. The scientists, from NRL's Materials Science and Technology Division, used a spin-polarized bias current from an iron (Fe) thin film contact and determined the strength of the interaction between spin-polarized electrons in the s, p and d shells.

A complete description of this work can be found in Physical Review Letters (28 November 2008).

Semiconductor QDs are nanoscale circular disks of one semiconducting material, typically 3 nm high by 30 nm in diameter, embedded within layers of a second material. Figure 1 shows such a structure, with an atomic force microscope image of the uncovered QDs in figure 2. Semiconductor QDs are attractive for a variety of quantum information processing, electronic and spintronic applications. In spintronic applications, the electron's spin rather than charge is used to store and process information. The International Technology Roadmap for Semiconductors has identified the electron's spin as a new state variable which should be explored as an alternative to the electron's charge for use beyond standard CMOS technology. The QD electronic structure exhibits the s,p,d,f shells characteristic of single atoms, so they are often referred to as "artificial atoms."

Semiconductor QDs are nanoscale circular disks of one semiconducting material, typically 3 nm high by 30 nm in diameter, embedded within layers of a second material. Credit: Naval Research Laboratory

The NRL researchers monitor the shell population and spin polarization by measuring the polarized light emitted as a function of the bias current from the Fe contact. In contrast with previous work, they resolve features in the electroluminescence (EL) spectra associated with the individual quantum levels (s-, p-, d-, and f- shells). As the bias current is increased, the shell states fill, and the EL from the QDs exhibits peaks characteristic of the shell energies, as labeled in figure 3.

Intershell exchange strongly modifies the optical polarization observed from that expected for simple models of shell occupation. From a detailed analysis of the EL spectra, the NRL researchers were able to obtain the first experimental measure of the exchange energies between electrons in the s- and p-shells, and between electrons in the p- and d-shells. These energies describe the degree of interaction between these quantum levels.

Source: Naval Research Laboratory

Explore further: New approach to form non-equilibrium structures

add to favorites email to friend print save as pdf

Related Stories

Social Security spent $300M on 'IT boondoggle'

9 hours ago

(AP)—Six years ago the Social Security Administration embarked on an aggressive plan to replace outdated computer systems overwhelmed by a growing flood of disability claims.

Cheaper wireless plans cut into AT&T 2Q profit

9 hours ago

(AP)—AT&T posted lower net income for the latest quarter due to cheaper cellphone plans it introduced as a response to aggressive pricing from smaller competitor T-Mobile US.

Awarded a Pell Grant? Better double-check

9 hours ago

(AP)—Potentially tens of thousands of students awarded a Pell Grant or other need-based federal aid for the coming school year could find it taken away because of a mistake in filling out the form.

Recommended for you

First in-situ images of void collapse in explosives

18 hours ago

While creating the first-ever images of explosives using an x-ray free electron laser in California, Los Alamos researchers and collaborators demonstrated a crucial diagnostic for studying how voids affect ...

New approach to form non-equilibrium structures

Jul 24, 2014

Although most natural and synthetic processes prefer to settle into equilibrium—a state of unchanging balance without potential or energy—it is within the realm of non-equilibrium conditions where new possibilities lie. ...

Nike krypton laser achieves spot in Guinness World Records

Jul 24, 2014

A set of experiments conducted on the Nike krypton fluoride (KrF) laser at the U.S. Naval Research Laboratory (NRL) nearly five years ago has, at long last, earned the coveted Guinness World Records title for achieving "Highest ...

User comments : 0