含钴纳米颗粒的半导体/颗粒膜异质结构的巨磁电阻效应
Giant magnetoresistance in semiconductor / granular film heterostructures with cobalt nanoparticles
摘要：
本文研究了SiO ${}_2$（Co）/GaAs和SiO ${}_2$（Co）/Si异质结构中的电子输运，其中SiO ${}_2$（Co）结构是含有Co纳米颗粒的颗粒状SiO ${}_2$薄膜.在SiO ${}_2$（Co）/GaAs异质结中观察到巨磁电阻效应。当电子从颗粒膜注入到GaAs半导体中时，该效应具有正值，并且具有温度峰型特征。该效应的温度位置取决于Co浓度，并且可以通过所施加的电场而移位。对于SiO_2 ${}_2$（Co）/GaAs异质结，掺杂浓度为71 at.% Co的磁电阻在室温下达到1000（$10^5$ %）。相反，对于SiO ${}_2$（Co）/Si异质结构，磁电阻值很小（4%），而对于SiO ${}_2$（Co）薄膜，磁电阻值则相反。SiO ${}_2$（Co）/GaAs异质结构中的高磁电阻效应是由磁场控制的碰撞电离过程在界面附近的半导体中形成的自旋相关势垒附近解释的。通过势垒并触发雪崩过程的电子的动能被施加的磁场减小。这种电子能量的抑制推迟了碰撞电离的开始，以更高的电场和巨磁电阻的结果。自旋相关势垒是由于半导体中积累电子层中的电子与Co的$d$ -电子之间的交换相互作用。
英文摘要：
We have studied the electron transport in SiO${}_2$(Co)/GaAs and SiO${}_2$(Co)/Si heterostructures, where the SiO${}_2$(Co) structure is the granular SiO${}_2$ film with Co nanoparticles. In SiO${}_2$(Co)/GaAs heterostructures giant magnetoresistance effect is observed. The effect has positive values, is expressed, when electrons are injected from the granular film into the GaAs semiconductor, and has the temperature-peak type character. The temperature location of the effect depends on the Co concentration and can be shifted by the applied electrical field. For the SiO${}_2$(Co)/GaAs heterostructure with 71 at.% Co the magnetoresistance reaches 1000 ($10^5$ %) at room temperature. On the contrary, for SiO${}_2$(Co)/Si heterostructures magnetoresistance values are very small (4%) and for SiO${}_2$(Co) films the magnetoresistance has an opposite value. High values of the magnetoresistance effect in SiO${}_2$(Co)/GaAs heterostructures have been explained by magnetic-field-controlled process of impact ionization in the vicinity of the spin-dependent potential barrier formed in the semiconductor near the interface. Kinetic energy of electrons, which pass through the barrier and trigger the avalanche process, is reduced by the applied magnetic field. This electron energy suppression postpones the onset of the impact ionization to higher electric fields and results in the giant magnetoresistance. The spin-dependent potential barrier is due to the exchange interaction between electrons in the accumulation electron layer in the semiconductor and $d$-electrons of Co.
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