Development of Room-temperature Ferromagnetic Nitride Semiconductors

Mn_4N 是钙钛矿衍生结构，被描述为 ABX_3 的化学形式，其中 A=Mn(I) 在角位置，B=N 在体中心，X=Mn(II) 在立方晶胞的面中心。 Mn(I)和Mn(II)的磁矩倾斜，净磁矩没有抵消。亚铁磁转变温度约为500C。我们对 Mn_4N 的第一原理能带结构计算表明，Mn d 态是金属性的，并且与 N 的 p 态良好杂化。上下自旋态共存于费米能级。另一方面，(Ga, Mn)N的能带结构计算表明，Mn d态很好地局域化，并显示出半金属态，在费米能级上给出了完美的自旋极化电子态。在这项工作中，我们成功地进行了亚铁磁Mn_4N和(Ga, Mn)N异质结构的MBE生长。在MBE工作中，我们使用NH_3作为N源，而不是具有RF等离子体激发的N_2-自由基单元。通过烘烤加热器将整个室加热至150℃左右，避免了MBE室内壁上NH_3的严重吸附。因此，MBE方法在这里被称为“热壁MBE”。然后，在生长过程中将NH_3压力稳定设定在1.0×10^-2Pa左右。首先生长了Mn_4N/GaN/Al_2O_3(0001)和Mn_4N/(Ga,Mn)N/Al_2O_3(0001)异质结构。 X射线衍射分析表明，在外延GaN和(Ga，Mn)N上形成了多晶Mn_4N层。在室温下观察磁光克尔旋转的磁滞曲线。对于两种结构，在平行于生长平面的 0.5T 磁场下，饱和克尔旋转角约为 0.01 度。 Mn_4N/GaN/(Ga, Mn)N 隧道磁阻 (TMR) 结构也已在 ITO 涂覆的石英衬底上生长。由于 TMR 结构，已观察到非线性电流-电压特性。在 70K 下，在垂直于 Mn_4N/GaN/(Ga, Mn)N 生长平面的磁场下，观察到磁阻的各向异性取决于通过 TMR 结构的电流方向。这表明通过 Mn_4N/GaN/(Ga, Mn)N TMR 结构进行自旋相关载流子整流。较少的

Mn_4N is perovskite-derived structure described as the chemical form of ABX_3 with A=Mn(I) at the corner positions, B=N at the body center and X=Mn(II) at the face centers of the cubic cell. The magnetic moments of Mn(I) and Mn(II) cant and the net magnetic moment is not cancelled. The ferrimagnetic transition temperature is around 500C. Our first-principles band-structure calculation of the Mn_4N shows that the Mn d states are metallic and well hybridize with p states of N. The up and down spin states coexist at, the Fermi level. On the other hand, the band-structure calculation of (Ga, Mn)N showed that the Mn d states are well localized and show the half metallic states giving the perfect spin-polarized electronic states at the Fermi level.In this work, we have succeeded in the MBE growth of the ferrimagnetic Mn_4N and the heterostructure with (Ga, Mn)N. In the MBE work, we used NH_3 as N source instead of N_2-radical cell with RF-plasma excitation. The serious NH_3 adsorption on the … More internal wall of MBE chamber was avoided by heating up the whole chamber at about 150C by baking heater. Hence, the MBE method is called here "hot-wall MBE". Then, NH_3 pressure was stably set around 1.0×10^<-2> Pa during the growth. Firstly, Mn_4N/GaN/Al_2O_3(0001) and Mn_4N/(Ga, Mn)N/Al_2O_3(0001) heterostructures have been grown. The X-ray diffraction analysis showed that the polycrystalline Mn_4N layer was formed on the epitaxial GaN and (Ga, Mn)N. The hysteresis curves of the magneto-optical Kerr rotation were observed at room temperature. The saturated Kerr-rotation angles were around 0.01 degree at the magnetic field of 0.5T parallel to the growth planes for both structures. Mn_4N/GaN/(Ga, Mn)N tunneling magneto-resistance (TMR) structure has been also grown on ITO-coated quartz substrates. The nonlinear current-voltage characteristic has been observed as due to the TMR structure. An anisotropy in the magneto-resistance depending on the current direction through the TMR structure has been observed under the magnetic field perpendicular to the Mn_4N/GaN/(Ga, Mn)N growth plane at 70K. This suggests the spin-dependent carrier rectification through the Mn_4N/GaN/(Ga, Mn)N TMR structure. Less