• PDF / 75,206 Bytes
• 1 Pages / 612 x 792 pts (letter) Page_size
• 37 Downloads / 195 Views

DOWNLOAD

REPORT

---

RESEARCH/RESEARCHERS Rectification Suppression in Magnetic-Ge Heterojunction Diode Shown to Be Magnetization-Dependent The potential for spin-polarized electronics to advance solid-state electronics by enabling logic and memory to be integrated into a single device or chip has prompted research efforts focused on spin-dependent effects in semiconductors. While electronic spin devices have previously shown relatively small effects, a team of researchers from the Department of Physics and Astronomy at the University of North Carolina in Chapel Hill has demonstrated the viability of producing multifunctional spin devices. As reported in the August 4 issue of Applied Physics Letters, F. Tsui, L. Ma, and L. He have observed magnetizationdependent diode behavior in a heterojunction consisting of a CoMn-doped p-type Ge magnetic semiconductor grown epitaxially on a lightly doped n-type Ge substrate. Under electrical bias, the current rectification of the diode can be suppressed by applying a magnetic field. The researchers grew magnetic germanium (M-Ge) films of the form Co2xMnxGe1-3x on Ge(001) substrates using molecular-beam epitaxy (MBE) techniques to create heterojunctions with x < 0.05 (see figure). However, the researchers only achieved smooth two-dimensional M-Ge growth and created heterojunctions with a good low-temperature, magnetization-dependent rectification effect for doping concentrations of x < 0.03. Below the 150°C Curie temperature (Tc) of this M-Ge film, a magnetizationdependent suppression of the current rectification effect, which was shown to be a consequence of the film’s ferromagnetic order, was reported. Under reverse bias and zero magnetic field (B = 0), the diode operated in the “on state” whereas, at either high magnetic field or under forward bias, the diode operated in the “off state” causing suppression of electron injection into the Ge substrate. At low temperature and a bias of -2 V, a current ratio of 30 was observed, which corresponds to a field-dependent current ratio, ∆I/I0, of 97%, that is, the ratio of the difference between the zero-field current and the current with an applied magnetic field, ∆I = I0 - I(B), to the zero-field current, I0 = I(B = 0). With a field on the order of 100 Oe, the current rectification was suppressed to half of its zero-field value. According to Tsui, “the low magnetic field required to cause the rapid and large suppression of current rectification makes this Ge-based magnetic heterojunction diode a technologically important device.” MRS BULLETIN/SEPTEMBER 2003

B

Figure. Schematic of the heterojunction with a doped magnetic Ge (M-Ge) film grown epitaxially on an n-type Ge(001) substrate (n-Ge). Reproduced with permission from Applied Physics Letters 83 (2003); © 2003 American Institute of Physics.

By examining the field-dependent current ratios as a function of the state variable for magnetization-dependent phenomena, µBB/kBT (where µB is the Bohr magneton and kB is the Boltzmann constant), the researchers demonstrated that the low field current ratios of