Electrically detected magnetic resonance (EDMR) is a

materials characterisation Characterization, when used in materials science, refers to the broad and general process by which a material's structure and properties are probed and measured. It is a fundamental process in the field of materials science, without which no scie ...

technique that improves upon

electron spin resonance Electron paramagnetic resonance (EPR) or electron spin resonance (ESR) spectroscopy is a method for studying materials that have unpaired electrons. The basic concepts of EPR are analogous to those of nuclear magnetic resonance (NMR), but the s ...

. It involves measuring the change in

electrical resistance The electrical resistance of an object is a measure of its opposition to the flow of electric current. Its reciprocal quantity is , measuring the ease with which an electric current passes. Electrical resistance shares some conceptual parallel ...

of a sample when exposed to certain

microwave Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequency, frequencies between 300 MHz and 300 GHz respectively. Different sources define different fre ...

frequencies. It can be used to identify very small numbers (down to a few hundred atoms) of impurities in

semiconductors A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. ...

Outline of technique

To perform a pulsed EDMR experiment, the system is first initialised by placing it in a magnetic field. This orients the

spin Spin or spinning most often refers to: * Spinning (textiles), the creation of yarn or thread by twisting fibers together, traditionally by hand spinning * Spin, the rotation of an object around a central axis * Spin (propaganda), an intentionally b ...

s of the

electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary partic ...

s occupying the donor and acceptor in the direction of the

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and t ...

. To study the donor, we apply a

pulse ("γ" in the diagram) at a resonant frequency of the donor. This flips the spin of the electron on the donor. The donor electron can then decay to the acceptor energy state (it was forbidden from doing that before it was flipped due to the

Pauli exclusion principle In quantum mechanics, the Pauli exclusion principle states that two or more identical particles with half-integer spins (i.e. fermions) cannot occupy the same quantum state within a quantum system simultaneously. This principle was formulated ...

) and from there to the valence band, where it recombines with a hole. With more recombination, there will be fewer conduction electrons in the

conduction band In solid-state physics, the valence band and conduction band are the bands closest to the Fermi level, and thus determine the electrical conductivity of the solid. In nonmetals, the valence band is the highest range of electron energies in ...

and a corresponding increase in the resistance, which can be directly measured. Above-bandgap light is used throughout the experiment to ensure that there are many electrons in the conduction band. By scanning the frequency of the microwave pulse, we can find which frequencies are resonant, and with knowledge of the strength of the magnetic field, we can identify the donor's energy levels from the resonant frequency and knowledge of the

Zeeman effect The Zeeman effect (; ) is the effect of splitting of a spectral line into several components in the presence of a static magnetic field. It is named after the Dutch physicist Pieter Zeeman, who discovered it in 1896 and received a Nobel priz ...

. The donor's energy levels act as a 'fingerprint' by which we can identify the donor and its local electronic environment. By changing the frequency slightly, we can study the acceptor instead.

Recent developments

EDMR has been demonstrated on a single electron from a

quantum dot Quantum dots (QDs) are semiconductor particles a few nanometres in size, having optical and electronic properties that differ from those of larger particles as a result of quantum mechanics. They are a central topic in nanotechnology. When the q ...

. Measurements of less than 100 donors and theoretical analyses of such a measurement have been published, relying on the P_b interface defect to act as the acceptor.

References

{{DEFAULTSORT:Electrically Detected Magnetic Resonance Quantum electronics Spectroscopy