【作者】 王丽；

【导师】 侯登录；

【作者基本信息】 河北师范大学 ， 凝聚态物理， 2012， 博士

【摘要】 在传统半导体工业中，Si一直是最基础的研究材料。过渡族元素掺杂IV族基半导体可以与现有的Si基微电子器件相集成，因此对于现代半导体工业的研究和集成，IV族基稀磁半导体（DMSs）具有更广泛的使用价值。近些年关于过渡族元素Mn掺杂IV族基DMSs的工作已被广泛研究，而其它过渡族元素（如：Fe、Cu、Cr等）的研究却为数不多。此外，由于样品中可能存在的第二相的干扰，使得样品铁磁性的来源仍是争论的话题。鉴于此，本文选取了过渡族元素Fe和Cu，利用非平衡的生长方法对IV族基半导体进行掺杂。为了准确的评价样品的铁磁性，我们采用更精准的测试手段对样品的微结构进行了表征。1、利用金属蒸发真空弧（MEVVA）和考夫曼源（Kaufman）技术，分别在室温与673K下制备了Fe、N离子共注入n-Si（100）基片。对于室温下制备的样品，X射线吸收精细结构（XAFS）表明低注入剂量(2.0×10¹⁶cm^-2)样品中大多数的Fe离子处于替代位，而高剂量(5.0×10¹⁶与2.0×10¹⁷cm^-2)注入样品中有反铁磁FeSi2化合物形成。磁性测试表明所有共注入样品具有室温铁磁性。FeSi2相的形成导致饱和磁化强度（MS）随着注入剂量的增加而减小。由于自退火效应的加强促使更多的FeSi2化合物形成，从而导致高基底温度下制备的样品的室温铁磁性弱于室温下制备的样品。样品的铁磁性来源于处于母体替代位的Fe离子。2、利用离子束溅射与MEVVA技术制备了不同注入剂量的Fe离子注入到Si_1-xGe_x（x=1、0.848、0.591、0.382、0.209、0.064、0）薄膜的系列样品。采用XAFS测试了Fe掺杂Si_1-xGe_x薄膜样品中Fe的局域微结构。结构分析表明低剂量的Fe离子注入到富Ge的Si_1-xGe_x薄膜（包括纯Ge薄膜）的退火样品中，几乎全部的Fe离子在母体中替代了Ge位，而高注入剂量的退火样品中大部分的Fe离子形成了反铁磁Fe₆Ge₅杂相。研究还发现，Fe在纯Ge薄膜中的固溶度最高，固溶度随着Si含量的增加而降低，并且退火可提高Fe在富Ge的Si_1-xGe_x薄膜中的固溶度。比较Fe离子注入Si_1-xGe_x薄膜（x=1、0.848、0.591）的制备态样品与退火样品，可发现室温下纯Ge系列的样品铁磁性最强，随着Ge含量的减少，铁磁性减弱。此外，退火可增加处于替代位的Fe离子的数量，从而导致退火后样品MS增大。通过实验与理论分析可知Fe离子掺杂富Ge的Si_1-xGe_x薄膜样品的铁磁性来源于Si_1-xGe_x母体与处于替代Ge位的Fe离子间的s, p-d交换相互作用，铁磁性是由电子载流子传递的，属于样品的本征铁磁性。3、利用离子束溅射与MEVVA技术制备了Fe离子注入Si_0.791Ge_0.209薄膜与Fe离子注入Si_0.773Ge_0.204C_0.023薄膜的两系列样品。XAFS测试了Fe在Si_0.773Ge_0.204C_0.023母体中的局域微结构。结构分析表明低剂量样品中的大多数的Fe离子在Si_0.773Ge_0.204C_0.023母体中处于替代Ge的位置，而在高剂量样品中有反铁磁Fe₆Ge₅相的存在。然而，在Fe离子注入Si_0.791Ge_0.209薄膜的样品中均有反铁磁的Fe₆Ge₅相形成。我们发现母体中有C的加入有助于母体与Si衬底晶格匹配度的提高，有利于Fe离子在该母体中处于替代位，可有效抑制Fe离子注入后杂质相的产生。磁性分析表明Fe掺杂Si_0.773Ge_0.204C_0.023薄膜的系列样品的室温铁磁性明显强于Fe掺杂Si_0.791Ge_0.209薄膜的系列样品。样品的铁磁性来源于在母体中替代Ge位的Fe离子，铁磁性由电子载流子传递，属于样品的本征铁磁性。4、用MEVVA和Kaufman源技术制备了Cu离子注入Si半导体样品与Cu、N离子共注入样品。结构分析表明所有样品均无第二相。当Cu离子注入到n型Si基底后转变为p型半导体，在p型环境中Cu离子以Cu+形式存在，导致Cu离子注入样品在室温下均显示为抗磁性。而Cu、N共注入样品均具有室温铁磁性，因为N离子的引入使载流子类型由Cu注入样品的p型转变为n型，n型环境有利于Cu²⁺的产生，共注入样品的室温铁磁性来源于电子载流子传递的Cu²⁺之间的交换相互作用。更多还原

【Abstract】 Si has been the most basic research material in the traditional semiconductor industry.Transition metal-doped group-IV semiconductors can be integrated with existing Si-basedmicroelectronic devices, so Si and Ge-based diluted magnetic semiconductors （DMSs） haveextensive value for the modern semiconductor industry. In recent years, Mn-doped groupIV-based DMSs have been extensively studied, but research on other transition metals （suchas Fe, Cu, Cr） has been comparatively less. In addition, the origin of the ferromagnetism isstill a topic in debate beacause there exist the disturbance of second phase in the samples.Considering that, we chose the transition elements Fe and Cu to dope group-IVsemiconductors by nonequilibrium growth method. The microstructure of the samples wascharacterized by much more accurate measurement in order to correctly evaluate theferromagnetism of the samples.1. Fe and N ions were co-implanted into Si wafers using the metal vapor vacuum arctechnique and Kaufman technique, prepare at room temperature and at673K, respectively.For the samples prepared at room temperature, X-ray absorption fine structure （XAFS）suggested that Fe ions existed in the matrix at isolated substitution sites in the low dosesample (2.0×10¹⁶cm^-2), while in the high dose samples of5.0×10¹⁶cm^-2and2.0×10¹⁷cm^-2,the non-ferromagnetic FeSi2phase formed. Magnetic measurements revealed that all thesamples showed room-temperature ferromagnetism. Due to the formation of FeSi2phase, thesaturated magnetization decreased with the increase of the implanted dose. Strengthening theeffect of the self-annealing can make for the formation of more FeSi2phase, which resulted inthe room-temperature ferromagnetism of the samples prepared at673K was weaker than thatof the samples prepare at room temperature. The origin of the ferromagnetism was from thesubstituted Fe ions randomly embedded in the Si matrix.2. A series of Si_1-xGe_x（x=1,0.848,0.591,0.382,0.209,0.064,0） thin films prepared byion beam sputtering were implanted with Fe ions to different doses using the metal vaporvacuum arc technique. XAFS was used to characterize the local microstructure around the Featoms in Fe-doped Si_1-xGe_xsamples. Structural analysis showed that for annealed samples of Ge-rich thin films （including pure Ge） implanted with low doses of Fe ions, almost all the Feions substituted at Ge sites. However, an anti-ferromagnetic Fe₆Ge₅impurity phase existed inthe annealed samples implanted with high doses of Fe. It was also found that the solubility ofFe ions was highest in pure Ge films and that with increasing Si concentration, the solubilitydecreased. Annealing was found to improve the solid solubility of Fe ions in Ge-rich thinfilms. Magnetic analysis showed that for the as-implanted and annealed samples of Ge-richthin films implanted with Fe ions, room-temperature ferromagnetism was strongest in thepure Ge series of samples and that as the Ge concentration decreased, the ferromagnetism atroom temperature weakened. In addition, annealing could increase the number of Fe ions atsubstitution sites, which resulted in the observed increase in the saturated magnetizationafterannealing. Experiment and theoretical analysis showed that the ferromagnetism ofFe-doped Ge-rich Si_1-xGe_xthin films samples originated from the s, p-d exchange interactionsbetween the Si_1-xGe_xmatrix and those Fe ions which substituted at Ge sites and that theferromagnetism was mediated by carriers.3. Thin films of Si_0.791Ge_0.209and Si_0.773Ge_0.204C_0.023were prepared by ion beamsputtering and were implanted with Fe ions to different doses using the metal vapor vacuumarc technique. XAFS was used to characterize the local microstructure around the Fe atoms inthe Fe-doped Si_0.773Ge_0.204C_0.023samples. Structural analysis showed that in theSi_0.773Ge_0.204C_0.023films implanted with low doses of Fe ions, almost all the Fe ions substitutedat Ge sites. However, an anti-ferromagnetic Fe₆Ge₅phase existed in the samples implantedwith high doses of Fe. On the other hand, in Fe-doped Si_0.791Ge_0.209samples, the Fe₆Ge₅phasewas present even when the lowest dose was implanted. We found that the introduction of theC was conducive to the improvement of the lattice matching degree between matrix and Sisubstrate, to the Fe ions preferentially residing at substitution sites and to the effectivesuppression of the formation of impurity phases. Magnetic analysis showed that theroom-temperature ferromagnetism of Fe-doped Si_0.773Ge_0.204C_0.023samples was clearlystronger than that of the Fe-doped Si_0.791Ge_0.209samples. The intrinsic ferromagnetism of theimplanted samples originated from the substituted Fe ions embedded in the matrix, and wasmediated by charge carriers. 4. Silicon semiconductor samples implanted with Cu ions and samples co-implanted withCu and N-ions were prepared by MEVVA and the Kaufman technique. None of the samplesshowed evidence of secondary phases. The initially n-type Si matrix, when implanted with Cuions, changed to a p-type semiconductor, and the Cu ions existed as Cu+in the p-typeenvironment. As a result, none of the Cu-implanted samples were ferromagnetic at roomtemperature. The co-implanted samples, on the other hand, showed room-temperatureferromagnetism because the introduction of N ions made the carrier type change from p-typeto n-type which is favorable for the appearance of Cu²⁺. The room-temperatureferromagnetism of the Cu and N co-implanted samples originated from the exchangeinteractions between of the Cu²⁺ions, mediated by electron carriers.更多还原