Growth and Characterization of Diluted Magnetic III-V Compound Semiconductors

研究了稀释磁性III-V半导体，特别是（In, Mn） As的分子束外延生长及其电、磁性能。以下是对研究结果的总结。分子束外延生长：在没有第二相（即MnAs）的情况下，可以并入InAs晶格的最大Mn浓度严重依赖于MBE生长过程中的生长温度。在300ºC时，x （in _<1-x>Mn_xAs）必须<0.03，导通为p型，而在200ºC时，x<0.25，导通为n型。外延层的特征：(1)磁性所有的n型样品都是顺磁性的，Mn离子之间的直接相互作用是反铁磁性的，最近邻J为-1.6 K。所有p型样品在中高温下均为顺磁性，但在低温下表现为自发磁化。顺磁分量仅在高磁场（4 ~ 9t）下饱和。自发磁化率占饱和磁化率的25%，在最低温度（1.4K）下研究了更多的磁化率。(2)电学性质n型样品在低温下表现为负磁阻。未观察到迟滞现象。p型样品的霍尔电阻主要受反常霍尔效应支配。当温度低于7.5 K时，磁滞与霍尔电阻呈负相关，并延伸至高磁场。滞回现象仅在p型样品中观察到。这可以用内部有倾斜自旋的大磁极化子的存在来解释。这种倾斜的起源被认为是空穴与锰离子之间的交换相互作用。由于Mn-Mn反铁磁相互作用的自旋轨道相互作用，这种相互作用主要是铁磁的，并带有自旋织构（即倾斜）。极化子的旋转引起自发磁化，而自旋与强磁场的排列导致在强磁场下的顺磁响应。这是第一次观察到弱铁磁性由于局域载流子自旋交换在稀释磁性半导体。少

Molecular beam epitaxial (MBE) growth and electric and magnetic properties of diluted magnetic III-V semiconductors, especially (In, Mn) As, are studied. Following is a summary of the research results. Molecular Beam Epitaxial Growth : Maximum Mn concentration that can be incorporated into InAs lattice without having second phase (which is MnAs) is critically dependent on the growth temperature during MBE growth. At 300ﾟC, x (in In_<1-x>Mn_xAs) has to be<0.03 and the conduction is p-type whereas at 200ﾟC, x<0.25 and n-type.Characterization of Epitaxial layers : (1) Magnetism All n-type samples are paramagnetic and the direct interaction between Mn ions is antiferromagnetic with nearest neighbor J of -1.6 K. All p-type samples are paramagnetic at medium to high temperatures, but show spontaneous magnetization at low temperatures. Paramagnetic component which saturates only at high magnetic fields (4 to 9 T) is also present. The spontaneous magnetization makes up for 25 % of saturation m … More agnetization at the lowest temperature (1.4K) investigated. (2) Electrical Properties n-type samples show negative magnetoresistance at low temperatures. No hysteresis is observed. The Hall resistance of p-type samples is dominated by anomalous Hall effect. At temperatures below 7.5 K, hysteresis appears in B dependence of Hall resistance together with negative magnetoresistance extending to high magnetic fields. Hysteresis is only observed in p-type samples. This can be explained by the presence of large magnetic polarons with canted spins inside. The origin of the canting is believed to be the exchange interaction between holes and Mn ions. The interaction is mostly ferromagnetic with spin texture (i. e. canting) due to spin-orbit interaction of to Mn-Mn antiferromagnetic interaction. Rotation of polarons gives rise to the spontaneous magnetization, whereas the alignment of spins with high magnetic fields results in paramagnetic response at high fields. This is the first observation of weak ferromagnetism due to localized carrier-spin exchange in diluted magnetic semiconductors. Less