Development of Room-temperature Ferromagnetic Nitride Semiconductors

Mn_4N是钙钛矿衍生结构，描述为ABX_3的化学形式，A=Mn(I)在立方晶胞的拐角位置，B=N在立方晶胞的体心，X=Mn(II)在立方晶胞的面心。Mn(I)和Mn(II)的磁矩不能被抵消，净磁矩不被抵消。铁磁转变温度在500℃左右。我们的第一原理能带结构计算表明，Mn_4N的d态是金属态，与N的p态杂化良好，上下自旋态在费米能级上共存。另一方面，对(Ga，Mn)N的能带结构计算表明，Mnd态具有良好的局域性，在费米能级上表现为半金属态，给出了理想的自旋极化电子态。在本工作中，我们成功地实现了亚铁磁性Mn4N的分子束外延生长和(Ga，Mn)N异质结。NH_3在…上的严重吸附用烘烤加热器将整个腔体加热到150℃左右，避免了更多的MBE腔内壁。因此，分子束外延方法在这里被称为“热壁分子束外延”。在生长过程中，NH_3压力稳定在1.0×10~(-2)~(-2)Pa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。X射线衍射分析表明，在外延GaN和(Ga，Mn)N上形成了多晶Mn4N层，在室温下观察到了磁光Kerr旋转的滞后曲线。在平行于生长面的0.5T磁场下，两种结构的饱和克尔旋转角都在0.01度左右。在ITO包覆的石英衬底上生长了Mn4N/GaN/(Ga，Mn)N隧道磁阻(TMR)结构。由于TMR结构的原因，观察到了非线性的电流-电压特性。在70K时，在垂直于Mn4N/GaN/(Ga，Mn)N生长面的磁场下，观察到磁阻随电流方向变化的各向异性。这表明了通过Mn4N/GaN/(Ga，Mn)N TMR结构的自旋相关的载流子整流。较少

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