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Abstract Ferromagnetic semiconductor Ga 1– x Mn x As 1– y P y thin films go through a metal–insulator transition at low temperature where electrical conduction becomes driven by hopping of charge carriers. In this regime, we report a colossal negative magnetoresistance (CNMR) coexisting with a saturated magnetic moment, unlike in the traditional magnetic semiconductor Ga 1– x Mn x As. By analyzing the temperature dependence of the resistivity at fixed magnetic field, we demonstrate that the CNMR can be consistently described by the field dependence of the localization length, which relates to a field dependent mobility edge. This dependence is likely due to the random environment of Mn atoms in Ga 1– x Mn x As 1– y P y which causes a random spatial distribution of the mobility that is suppressed by an increasing magnetic field.
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This content will become publicly available on March 1, 2026
Off-state magnetoresistance in long-channel germanium Schottky-barrier MOSFETs
An increasing magnetic field perpendicular to an undoped semiconductor surface at low temperature is known to strengthen the binding of localized electrons to stationary ions, as the wavefunction's tails evolve from exponential to Gaussian. It is also known that application of a high bias voltage to a depleted semiconductor can liberate bound charge and induce a large drop in electrical resistance. We connect these established results to experimental electrical transport measurements on off-state germanium Schottky-barrier metal–oxide–semiconductor field-effect transistor (MOSFETs) with an aluminum oxide insulating dielectric and platinum germanide contacts. We make measurements at the three distinct orientations of the magnetic field with respect to the substrate and the current. At 6 K, we observe sharp attenuation of current by more than 2 orders of magnitude, within 60 mT, at a crossover magnetic field perpendicular to the substrate. A 1 T magnetic field attenuates the current by more than 4 orders of magnitude. The strength of the attenuation and the value of the crossover field are controlled by both the gate–source and drain–source voltages. The attenuation is much weaker when the magnetic field is parallel to the current. Finally, we orient the magnetic field parallel to the substrate, but perpendicular to the current, allowing us to distinguish charge hopping at the oxide interface from charge hopping in the bulk. This large off-state magnetoresistance can be exploited for cryogenic magnetic- and photo-detection, and for high-bias, low-leakage MOSFETs.
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- Award ID(s):
- 2409911
- PAR ID:
- 10612927
- Publisher / Repository:
- AIP
- Date Published:
- Journal Name:
- Applied Physics Letters
- Volume:
- 126
- Issue:
- 9
- ISSN:
- 0003-6951
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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