Role of Hydrogen in Variation of Electrical, Optical and Magnetic Properties of ZnSe-Fe Bilayer Thin Films Structure
2014-03-21 02:35:26 《Energy Science and Technology》 2013年4期
This paper is reporting the role of hydrogen in preparation and characterization of dilute magnetic semiconductor of ZnSe-Fe bilayer thin film structure. These films are hydrogenated at different pressure to see the effect of hydrogen on electrical， optical， magnetic and structural properties of bilayer structure. Optical absorption in thin films is found to be decrease with hydrogen absorption. It may be due to interaction of hydrogen with bilayer structure and takes electron from the conduction band of thin film structure. The current-voltage characteristic of these films shows the variation in conductivity with hydrogenation due to decrease in electron density. Atomic Force Microscopy and scanning electron Microscope recorded to see the surface topography of bilayer thin films. It has been observed that deposited film have nano size structure that is favorable for hydrogen absorption having higher surface to volume ratio. The Electron diffraction X-ray analysis gives the information about composition of films. Raman spectra have used to see the presence of hydrogen. Super-conducting Quantum Interference Device gives the information of confirmation of diluted magnetic semiconductors and variation of magnetic momentum with hydrogenation.
Key words： Thin film； Atomic Force Microscopy； X-ray diffraction； Scanning electron microscope（SEM）； Electron diffraction X-ray analysis （EDAX）； Hydrogenation Mangej Singh （2013）. Role of Hydrogen in Variation of Electrical， Optical and Magnetic Properties of ZnSe-Fe Bilayer Thin Films Structure. Energy Science and Technology， 6（2）， 71-78. Available from： URL： http：//www.cscanada.net/index. php/est/article/view/10.3968/j.est.1923847920130602.2843 DOI： http：//dx.doi.org/10.3968/j.est.1923847920130602.2843
Modern information technology utilizes the charge degree of freedom of electrons to process information in semiconductor and spin degree of freedom for mass storage of information in magnetic materials. If both charge and spin degrees of freedom are available in semiconductors then we are able to create new functionalities and enhance the performance of existing devices. To do so， we required to create sustain， transport， control of spin and also detect spins in semiconductors， which is a challenge for semiconductor physics， materials and science technology.
In recent years there is a tremendous research interest in the introduction of ferromagnetic property at room temperature in semiconductors to realize a new class of spintronic devices such as spin valve transistors， spin light emitting diodes， non-volatile memory， logic devices， optical isolators and ultra-fast optical switches （Chambers， 2002）. Diluted magnetic semiconductors （DMS） have been studied actively for the use of both charge and spin of electrons in semiconductors. Spin injection into nonmagnetic semiconductors was trying by many research groups to offer a new classes of spintronic devices. Diluted magnetic semiconductors， in which transition metals are doped into semiconductors exhibiting room temperature ferromagnetism， have also attracted much attention for their potential uses in spintronic devices （Pan， Song， Liu，
Yang， & Zeng， 2008）. The use of carrier spins， in addition to carrier charges， of spintronic devices looks promising research field of magnetic recording media （Pearton， et al.， 2003）. The advantages of diluted magnetic semiconductor（DMS） based spin-electronic devices include enabling of instant-on computer， increased integration density， higher data processing speed， low electrical energy demand and compatibility of their fabrication processes with those currently used in industry.
Banerjee and Ghosh （2008） fabricated Cd1-xMnxTe thin films using thermal inter-diffusion of multilayers of sputtered compound semiconductors. They had observed that addition of Mn-content in CdTe has resulted increase band gap and also activation energy but found decrease in resistance under illumination. Single crystal of Zn1-xMnxTe was prepared successfully by vertical Bridgman technique for different concentration of Mn and it was also found that band gap increases with increasing concentration of Mn （Brahmam， Reddy， & Reddy， 2005）. Daboo et al studied the switching behavior of Fe/GaAs samples for various values of uniaxial and cubic anisotropy constants using in-plane MOKE magnetometer （Daboo， et al.， 1994）. Growth of Fe-films on ZnSe epilayers and bulk GaAs substrates investigated by Bierleutgeb Sitter， Krenn， and Seyringer， （2000） to determine the mode of film growth as well as structural properties of the films. The effect of varying Fe and ZnSe semiconductor layers thickness on the magnetic and electronic properties of the super lattice analyzed by Continenza， Massidda， and Freeman（1990）. They had found that Fe magnetism recovers its bulk characteristics and the enhanced magnetic moment was quickly suppressed as the number of layer increased. Meckenstock， et al. （2002） investigated the Magnetic properties of Fe/ZnSe and Fe/GaAs hetero-structures by ferromagnetic resonance and SQUID measurements and found that （001） Fe-films on GaAs and ZnSe substrates show steps in the hysteresis. Kerbs， Jonker， and Prinz（1987） reported the magnetic properties of single-crystalα-Fe films grown by molecular beam epitaxy （MBE） on both （110） and （001） ZnSe epilayers. The origin of the uniaxial in-plane anisotropy found in （110） Fe/ZnSe and（110） Fe/GaAs films is attributed to the combination of magneto restriction and the lattice mismatch-induced strain originating at the Fe/substrate interface. It was found that Fe/ZnSe films have more attractive properties to compare Fe/GaAs.
Hydrogen is an important impurity in many semiconductors because of its tendency to form complexes with most crystal defects and impurities. In combination with its presence during crystal growth and processing， hydrogen has gained both fundamental and technological interest （Pankove， & Johnson， 1991； Pearton， Corbett， & Stavola， 1992； Pearton， 1994； Estreicher， 1995； Pavesi & Giannozzi， 1992） because hydrogen strongly affects the electronic properties of materials. Extensive experimental and theoretical work on hydrogen in silicon has led to a more detailed understanding of its properties in this material compared to all other semiconductors. Interstitial hydrogen is a fast diffuser. It can bind with native defect or other impurities， often eliminating their electrical activity-a phenomenon known as passivation. Electrical measurements such as current/voltage provide detailed information about the electronic effects of hydrogen. Nehara et al （2009） observed the effect of hydrogen on electrical properties of CdTe/Mn bilayer thin films and suggested variation in electrical properties with hydrogenation. Thevenard et al （2007） prepared perpendicularly magnetized （Ga，Mn） As layers using a monoatomic hydrogen plasma and suggested that original magnetization reversal phenomena arise from the presence of a soft magnetic interface between the ferromagnetic and paramagnetic regions， and that undergoing hydrogenation indeed leads to their efficient passivation. The reduction of Hole density resulted in strong modifications of their ferromagnetic properties. In particular， Thevenard， Largeau， Mauguin， Lemaitre， and Theys （2005） observed in magnetotransport experiments that the decrease of the Curie temperature， along with modifications of the magnetic anisotropy， a behavior consistent with the mean-field theory. Hydrogen can also induce electrically active defects， adsorption of hydrogen on the TiFe （110） surface covered by palladium monolayer was investigated by Kulkova， Eremeev， Egorushkin， Kim， and Oh （2003） using the full potential linearized augmented plane wave method within the local density approximation. An author Park et al. （2007） observed that the interstitial hydrogen leads to the changes in the magnetic hysteresis loop as well as the enhancement of carrier concentrations in the Mn-doped ZnO film. Hydrogen molecules at normal pressure are infrared inactive due to their lack of dipole moment， but studied by Raman scattering （Stoicheff， 1957） gives information that hydrogen strongly affects the optical properties of diluted magnetic semiconductors. It was also observed that optical transmission spectra found to decrease and optical band gap found to increase due to the hydrogenation in CdTe-Mn bilayer DMS thin films （Nehra & Singh， 2009）. The Raman spectroscopy carried out by many authors to get information about the presence of hydrogen in semi conducting materials（Vetterhoffer， Wagner， & Weber， 1996； Pritchard， Ashwin， Tucker， Newman， & Lightowlers， 1996； Leitch， Alex， & Weber， 1998）.
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