Semiconductor-Based Magnetic Switching Device

Wednesday, 8 October 2014: 17:00
Expo Center, 1st Floor, Universal 5 (Moon Palace Resort)
S. Joo (KRISS), B. Lee (Inha University), and K. Rhie (Korea University)
Recently, large magnetoresistance (MR) has been observed at high electric fields in nonmagnetic semiconductors, such as Au/GaAs Schottky diodes [1], boron- and phosphorus-doped Si [2-4], and Si metal oxide-semiconductor field-effect-transistors [5]. This large MR effect is responsible for the magnetic field-dependent impact ionization process. Because the magnetic field-dependent impact ionization is affected by the band-gap of the semiconductor and the effective mass of the charge carriers, a small band-gap is preferred for the manipulation of impact ionization at a low bias voltage, and a smaller effective mass provides faster acceleration by Lorentz forces, making the device more sensitive to the magnetic field.

In this report, our device has been fabricated by use of HgCdTe & GaAs whose band-gap is 0.107 eV & 1.42 eV, electronic effective mass is 0.008 & 0.063 times of that of the free electrons. The resistive state is varied abruptly by applying a magnetic field. The responsible mechanism of our device is discussed, and theoretical calculations for the simulation of the experimental data are carried out.

  Current is measured in step with bias voltage sweep or magnetic field sweep. When the current values change abruptly, the current measurement is repeated until the collected data approach a roughly continuous plot. All measurements are carried out at low temperature.

Our data show dependence of the current on the magnetic field at various bias voltages. They show abrupt decrease of the current as the magnitude of magnetic field increases. The magnitude of the current variation according to the magnetic field is extraordinarily large. Our device exhibited more than three orders of magneto-conductance change for GaAs. The upper bound of the current is intentionally limited to be 10 μA to protect the device from high current damage. Thus, owing to this large magneto-conductance our device can be referred to as a magneto-switch rather than an ordinary magneto-conductance device.

This large magneto-conductance effect is caused by the magnetic field dependent impact ionization process. The magnetic field affects the impact ionization through Lorentz force. When magnetic field is applied perpendicular to the current direction; the Lorentz force deflects the electronic trajectory and hinders electrons from acquiring kinetic energy. Thus, under a magnetic field a longer trajectory is needed to acquire kinetic energy, but this longer trajectory leads to possibly more inelastic scatterings and suppression of the impact ionization. In order to restore the impact ionization, more electric field is required to lift their kinetic energy, and these result in the increase of the threshold voltage of the device in the presence of a magnetic field.

The huge difference in current values near the threshold magnetic field in the present device can give rise to a large on/off ratio as a switching device. This novel device can be a good candidate as an electrical switching device controlled by a magnetic field. This large magneto-conductance effect is due to change the impact ionization process through Lorentz force by magnetic field.

[1] J. S. Moodera and P. Leclair, Nature Materials 2, 707 (2003).

[2] A. Asamitsu, Y. Tomioka, H. Kuwahara and Y. Tokura, Nature 388 , 50 (1997).

[3] M. P. Delmo, S. Yamamoto, S. Kasai, T. Ono and K. Kobayashi, Nature 457, 1112 (2009).

[4] J. J. H. M. Schoonus, F. L. Bloom, W.Wagemans, H. J. M. Swagten, and B. Koopmans, Phys. Rev. Lett. 100, 127202 (2008).