13:14 08/10/2019 | 7newstar.com
Total post : 1,195
IBM claims to have discovered a technique enabling the extraction of even more information from carriers
(Tech) Several studies following the Hall effect’s discovery sought to examine the extent to which the measurement could be performed with photons. In these early photo-Hall experiments, light illumination was used to generate multiple carriers or electron-hole pairs in semiconductors. But because the basic Hall effect provides insights only into the dominant charge carrier, no attempt was successful in revealing the properties of both carriers simultaneously.
By contrast, this latest approach starts with a known majority carrier density from the traditional Hall measurement in the dark. Light with a known illumination intensity is then introduced, enabling the discovery of the carrier lifetime and both the majority and minority carrier mobility and density.
New measuring devices make it easier to orchestrate than before - namely, a tool called the parallel dipole line (PDL) trap. IBM scientists developed the PDL four years ago while investigating the camelback effect, which occurs between two lines of transverse dipoles when they exceed a critical length. But these researchers later discovered that when rotated the PDL serves as an ideal system for photo-Hall experiments, partly because of the ample space it provides for large area illumination onto samples.
As it turns out, clean Hall signal measurements can be challenging to execute when the signal is weak or unwanted noise is present, such as under lights. They’re best performed with systems like the PDL, which provides an oscillating magnetic field. CRPH helpfully selects both the desired frequency of the target signal and the phase of the field with a method called lock-in detection.