All electrical measurement of spin injection in a magnetic $p\text{−}n$ junction diode

Magnetic $p$-$n$ junction diodes are fabricated to investigate spin-polarized electron transport. The injection of spin-polarized electrons in a semiconductor is achieved by driving electrons from a ferromagnetic injector (Fe), into a bulk semiconductor $\left(n\text{−}\mathrm{GaAs}\right)$ via Schottky contact. For detection, a diluted magnetic semiconductor $\left(p\text{−}\mathrm{GaMnAs}\right)$ layer is used. Clear magnetoresistance was observed only when a high forward bias was applied across the $p$-$n$ junction.

Figure 1

(Color online) (a) Band-energy schemes for the magnetic $p$-$n$ junction with a $\mathrm{Fe}∕\mathrm{GaAs}$ Schottky barrier. The $p$ region (left) is magnetic $\mathrm{GaMnAs}$ layer, indicated by the spin splitting of the conduction band. Under applied forward bias, the spin-polarized electrons (solid circles) are injected from Fe (right) to the $n\text{−}\mathrm{GaAs}$ region (middle) and extracted across the depletion layer into the $p$ region. Up and down arrows indicate the magnetizations of the two electrodes. (b) The cross section of the device geometry with four-probe measurements.

Figure 2

(Color online) Logarithmic plot of forward $I$-$V$ characteristic of the magnetic $p$-$n$ junction diode at room temperature. The dashed lines represent the theoretical slopes of the curve, indicating the $I$-$V$ characteristic dominated by the $p$-$n$ junction and Schottky diode, respectively. The inset shows the $I$-$V$ curves of the device at $4.2\mathrm{K}$ (dashed line) and room temperature (solid line).

Figure 3

(Color online) (a) SQUID magnetic measurements of the $\mathrm{GaMnAs}$, Fe, and $\mathrm{Fe}∕\mathrm{Co}$ films at $10\mathrm{K}$. (b) Magnetoresistance of the device $(p\text{−}\mathrm{GaMnAs}∕n\text{−}\mathrm{GaAs}∕\mathrm{Fe}∕\mathrm{Co})$ plotted as a function of magnetic field in the plane. The in-plane magnetic field is along [110] (b1), perpendicular to [110] (b2) and along [1$\overline{1}$0] (b3). The alignment of the electrodes is indicated by arrows in (b1). (c) Magnetoresistance curve of the reference sample $(p\text{−}\mathrm{GaMnAs}∕n\text{−}\mathrm{GaAs}∕\mathrm{Fe})$. Constant resistance is observed.

Figure 4

Magnetoresistance signal versus voltage. The solid line is a guide to the eye.