N型稀磁半导体Ge_(0.96–x) Bi_xFe_(0.04)Te薄膜的磁电性质研究

GeTe基稀磁半导体材料因具有可独立调控载流子浓度和磁性离子浓度的特性而受到广泛关注.本文利用脉冲激光沉积技术制备了该体系的单晶外延薄膜,并通过高价态Bi元素部分取代Ge元素的方法实现了材料中载流子类型从空穴向电子的转变,即制备出N型GeTe基稀磁半导体.测量结果表明,无论是室温还是低温下的Hall电阻曲线皆呈现负斜率,说明体系中载流子是电子;并且当Bi掺杂量达到32%时,电子浓度为10~(21)/cm~3.变温输运性质的测量证明体系的输运行为呈现半导体特征.通过测量低温10 K下的绝热磁化曲线,在高Bi掺杂体系中观测到了明显的铁磁行为,而低于32%Bi掺杂量的体系中未观察到.这一结果说明,高掺杂Bi的替代导致载流子浓度的增加,促进了载流子传递Ruderman-Kittel-Kasuya-Yoshida相互作用,使得分散的Fe-Fe之间产生磁耦合作用,进而形成铁磁有序态.

Magnetic and eletronic transport properties in n-type diluted magnetic semiconductor Ge0.96-xBixFe0.04Te film

The epitaxial thin films of Ge_0.96-xBi_xFe_0.04Te are deposited on BaF₂ substrates by using pulsed laser deposition technique. The thin films with three different compositions i.e. Ge_0.8Bi_0.2Te, Ge_0.76Bi_0.2Fe_0.04Te, and Ge_0.64Bi_0.32Fe_0.04Te are prepared in this wok. Their high-quality epitaxy and crystallinity are confirmed by X-ray diffraction and atomic force microscopy. According to the measurements of Hall effect variation, we find that each of all curves exhibits a negative slope for the different films as the temperature varies from low temperature to room temperature, indicating that Ge_0.96-xBi_xFe_0.04Te films are n-type material because the substitution of Bi for Ge makes the carriers change from holes into electrons. Temperature dependence of resistivity confirms that the electronic transport behavior for each of Ge_0.96-xBi_xFe_0.04Te thin films exhibits a typical semiconductor characteristic. From the measurements of temperature dependence of electronic transport under various external magnetic fields, we find that the Ge_0.64Bi_0.32Fe_0.04Te thin film shows some magnetoresistive effect while other composition films do not possess such a property. Based on the linear fitting of temperature dependence of magnetic susceptibility in high temperature and low temperature region, the magnetic property of Ge_0.64Bi_0.32Fe_0.04Te thin film changes from 253 K. Together with the study of magnetic susceptibility curve in the paramagnetic region, the Curie-Weiss temperature is determined to be 102 K. At a low temperature of 10.0 K, we observe an obvious ferromagnetic hystersis loop in Ge_0.64Bi_0.32Fe_0.04Te instead of in Ge_0.76Bi_0.2Fe_0.04Te thin film. These results imply that the increase of Bi dopant is main reason for the establishment of ferromagnetic ordering state. The carrier concentration increases and thus promotes the carriers transporting the Ruderman-Kittel-Kasuya-Yoshida interaction, thereby leading to the separated Fe ions producing the magnetic interaction and forming an n-type diluted magnetic semiconductor.