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Preparation and Magnetic Research of Cr(Co) Doped Ge(Si) Based Diluted Magnetic Semconductor

Author: HuYuZuo
Tutor: HouDengLu
School: Hebei Normal
Course: Condensed Matter Physics
Keywords: Diluted magnetic semiconductor magnetron sputtering substitutional site interstitial site ferromagnetism
CLC: O472.5
Type: Master's thesis
Year: 2010
Downloads: 64
Quote: 0
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Abstract


Diluted magnetic semiconductor (DMS) has two sets of freedom degrees---charge and spin in the same matrix, along with the charge characteristics in conventional semiconductors and the spin in magnetic materials, become the best candidates materials for semiconductor spintronics devices. In recent years, Ge/Si-based DMSs attract considerable experimental effort due to the compatibility with mainstream silicon technology.At present, Ge/Si-based diluted magnetic semiconductor (DMS) materials have become a hot research topic at home and abroad. Although there have been many better results in both theoretic and experimental fields, some questions are still to be further solved, such as the origin of the observed ferromagnetism, the lower Curie temperature and so on. Therefore, in this work, we reported that series of Cr (Co) doped Ge (Si) films deposited on the n-Si (100) substrates were prepared by magnetron sputtering method. The structural, magnetic and electronic properties are also discussed in order to elucidate the ferromagnetism of the films.1. Series of Cr:Ge and Cr:SiX-ray diffraction (XRD) measurements suggest that no indication of a secondary phase was found in either sample, and all the samples show intrinsic Ge or Si structure respectively. Electrical transport properties indicate that chromium introduces a shallow acceptor level. Cr ions not only provide localized spins but also as s acceptor centers that provide holes. X-ray photoelectron spectroscopy (XPS) measurements indicate that the majority of Cr atoms exist in the bivalent state, containing a small amount of Cr3+. X-ray absorption fine structure spectroscopy (XAFS) show that the Cr ions are situated in interstitial sites in the Si matrix, other than in the substitutional sites in the Ge matrix. Magnetic property measurements showed that CrxGe1-x films show low temperature ferromagnetism. The ferromagnetism arises from the p-d exchange coupling between the localized p electron of the Ge atoms and the d electron of the Cr atoms. But the origin of the ferromagnetism of the CrxSi1-x films was unclear, and further experiments shloud be necessary in the future.2. Series of Co:SiNo indication of a secondary phase was found in either sample, and all the films exhibit a Si (311) preferred orientation. X-ray photoelectron spectroscopy results indicated that the doped Co ions in the films were in the divalent state. The orders of the resistivities of all the samples are 104Ω·cm, and increased with Co content increasing, indicate that chromium introduces a deep acceptor level. Magnetic measurements showed that Co doping could induce room-temperature ferromagnetism, which the coercive force and remanence were very low. The observed ferromagnetism maybe were induced by the hybridization between the localized d electron of the Co ions and the p electron of the Si atoms.

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