Growth Dynamics and Properties of Compound Semiconductor Layers Prepared by Low Temperature Molecular Beam Epitaxy

为了在半导体中注入自旋极化电流，我们利用分子束外延再生长技术制备了铁磁/非磁性半导体异质结，并研究了它们的电流-电压特性和电致发光极化。研究结果总结如下：在分子束外延制备的铁磁半导体(Ga，Mn)As/非磁性半导体(In，Ga)As pn结发光二极管中成功地实现了对非磁性半导体的电子自旋注入。我们在铁磁/非磁性pn结的电致发光光谱中观察到了滞后极化。剩余电致发光偏振度约为±1%，其磁化强度几乎与温度成正比。我们在晶格松弛的n-In_xGa_(lt；1-x&gt；As(…))衬底上制备了铁磁性(Ga，Mn)As/非磁性(In，Ga)As半导体发光二极管更多的x=0.15-0.18)缓冲层，使(Ga，Mn)As的易磁轴垂直于平面。为了弄清(Ga，Mn)As/GaAs异质结界面价带排列，我们制备了(Ga，Mn)As/i-GaAs/p-GaAsp-i-p结构，并测量了它们的伏安特性随温度的变化关系。发现这种p-i-p结构的电流-电压特性依赖于偏置电压的极性，这表明当空穴电流从(Ga，Mn)As注入到GaAs中时，界面处存在势垒。假定电流主要是肖特基势垒上的热发射，我们对结果进行了分析，发现由(Ga，Mn)As的费米能测得的势垒高度约为100 meV，这与(Ga，Mn)As中的Mn浓度无关。较少

In order to inject spin-polarized electrical current into semiconductors, we fabricated ferromagnetic/nonmagnetic semiconductor heterostructures by employing MBE regrowth technique, and investigated their current-voltage characteristics and electroluminescence polarization. The summary of the research results is as follows :Electrical spin injection into nonmagnetic semiconductor is successfully achieved in ferromagnetic semiconductor (Ga, Mn) As/nonmagnetic semiconductor (In, Ga) As pn junction light emitting diodes prepared by molecular beam epitaxy. We observed hysteretic polarization in electroluminescence spectra of ferromagnetic/nonmagnetic pn junction. The degree of the remanent electroluminescence polarization was about ±1%, of which the temperature dependence is almost proportional to that of the magnetization of (Ga, Mn) As.We fabricated ferromagnetic (Ga, Mn) As/nonmagnetic (In, Ga) As semiconductor light emitting diodes, which are grown on lattice-relaxed n-In_xGa_<1-x>As ( … More x=0.15-0.18) buffer layer so that the magnetic easy axis of (Ga, Mn) As directs perpendicular to the plane. We measured the degree of the polarization of light emitted from the backside of the substrate, and observed hysteretic polarization.In order to clarify the valence band alignment at (Ga, Mn) As/GaAs heterointerface, we fabricated (Ga, Mn) As/i-GaAs/p-GaAs p-i-p structures with different Mn concentration in (Ga, Mu) As, and measured the temperature dependence of current-voltage characteristics of them. It is found that the current-voltage characteristics of such p-i-p structures depend on the polarity of bias voltage, which suggest the existence of a potential barrier at the interface when hole current is injected from (Ga, Mn) As into GaAs. Assuming that the current is dominated by thermal emission over a Schottky barrier, we analyzed the results and found that the barrier height measured from the Fermi energy of (Ga, Mn) As is about 100 meV, which does not depend on the Mn concentration in (Ga, Mn) As. Less