Study Of Raman Scattering On Zno-based Semiconductors

As a fast, effective, nondestructive and contactless technique, Raman Scattering has been proved to be playing the key role in diagnosing the internal structure of molecules and crystals of condensed matter physics. We have studied the basic physical properties such as the phonon, electron, and the interaction between them based on the Raman and luminescence spectroscopy.It is well known that semiconductor lighting has obtained much attention due to the international energy shortage issue. The key technique of semiconductors lighting is to develop novel blue to UV light emitting diodes (LEDs). Recently, ZnO is promising in blue and UV LED. However, due to the self-compensation effect from native defects and the low solubility of the acceptor dopants in ZnO, high acceptor doping seemly becomes necessary to obtain p-ZnO, which will result in the low hole mobility. So its application is always limited by the p-type bottleneck. A further understanding of p-type ZnO thin films is essential for overcoming the p-type difficulty.In this dissertation, we have presented a comprehensive investigation of temperature dependence of Raman scattering of the CPPM in N-In codoped p-type ZnO films with different hole densities grown on Si substrates by USP in the temperature range from 83 to 578 K. The frequencies and linewiths of the CPPM can be well described by a theoretical model. The downshift of frequencies and broadening of linewidth are mainly due to the anharmonic effect. Through detailed theoretical modeling, we have determined the decay process of the CPPM. The anharmonic constants increase with hole density and the lifetime reduces with increasing anharmonicity. Furthermore, it is found that the contribution of four-phonon process increases while that of three-phonon precess reduces with increasing hole density, which can be attributed to the increase of LPDOS.On the other hand, new type high performance and low cost UV detector is under intensive investigation for its extensive application in many area such as micro-electronics, environmental monitoring, fire warming, biology, space research and missile warning systems. Compared with GaN-based materials, ZnO-based is more suitable for the fabrication of a UV detector, due to low-growth temperature, simpler crystal-growth technology, low-growth cost, absence of toxicity, and abundance in nature, etc. However, unlike the mature Si/Ge materials and compounds, the ZnO-based materials are still in their initial stages, and many physical properties or parameters of them remain ambiguous. In this dissertation, we have modulated the bandgap of ZnO films by substituting Mg for Zn to grow ZnMgO, and grown wurtzite structure of ZnMgO thin films with bandgap from 3.26 to 3.99 eV. Furthermore, we have also studied Raman Scattering of ZnMgO.We have presented a detailed micro-Raman investigation of temperature dependence Raman spectra of A1(LO) and E1(LO) modes in hexagonal ZnMgO films with different Mg compositions (x≤0.323) in the temperature range from 83 to 578 K. In combination with the same theoretical modellings for the frequencies downshift and linewidths broadening, we have clearly illustrated the temperature effect on the phonon frequency and linewidth. The work demonstrates that the micro-Raman technique is very useful in monitoring the local temperature during the ZnMgO-based device operation with submicrometer spatial resolution.As a potential candidate for future generation of semiconductor device, Nickel silicide (NiSi) has attracted much attention in the past decade. Depite of well-orcognized advantange of NiSi, there are still some challenges to overcome. On the one hand, the agglomeration and compatibility with germano silicides and transformation of NiSi to high-resistivity NiSi2 phase at high annealing temperatures seriously limit the silicidation process window. The prominent work of Mangelinck et al. that the addition of only 5% of Pt significantly enhances the thermal stability of NiSi has emerged a fertile ground for investigation of the third element addition to NiSi films. By X-ray diffraction measurements and calucation in the frames of the classical nucleation theory, the addition of high-cost Pt, Pd, and Rh seems to suit perfectly the aims of the stability improvement up to 900 oC up to now. Very recently, a number of reports of have also suggested the addition of cheaper metals such as Mo, Zr, and Co to NiSi, showing the retardation of NiSi2 formation, although not as effective as the former alloys, only up to the temperature of 800 oC. Since there is no unambiguous decision on which additive to use, engineers still have to employ the"expensive"ones to satisfy the shrinking dimension demand of microelectronics. Pd is preferable as it costs four times less than that of Pt while it exhibirs comparative properties. On the other hand, thermal degradation issues of microelectronic materials are a dominating concer today and precise knowledge of the actual surface temperature of silicides especially during device operation is critical for device reliability.In this dissertation, we report on a systematic Raman study on NiPdSi film and a solid comparison with pure NiSi film under different annealing temperatures. We have demonstrated that this technique is perfectly applicable for both the identification of phase transition temperature and phonon dynamics in NiPdSi. It is verified that the addition of Pd is efficient in retardation in the formation of NiSi2 up to 900°C, which provides a significant extension of the silicide process window. We have further shown that the anharmonic effects of phonon decay dominate the Raman frequency downshift with increasing temperature, and as compared to the pure NiSi case, the presence of Pd in NiSi can reduce the Raman frequency downshift for about 4 cm?1, giving an additional evidence of a favorable use of NiPdSi for microelectronic applications.RRS has the advantage compared to other optical measurements, since it provides information about both the lattice dynamics and electronic structure of materials. This technique is especially important for alloy semiconductors, where the alloy-induced disorder perturbs the interaction between the lattice vibrations and electronic states, and introduces localized excitons in the forbidden gap shown as sharp resonance features in RRS. A key issue in optimizing semiconductor diode lasers concerns the microscopic mechanism responsible for gain and stimulated emission, which can be appropriately examined by the strong localized excitonic effects. Therefore, RRS has been demonstrated to be an important tool in studying the optoelectronic properties of alloy semiconductors, and widly used in it.We have presented an easy and effective way to comparatively investigate the RRS of LO phonons in hexagonal Zn1-xMgxO (x≤0.323) thin films. The resonance effect is achieved by changing the Mg composition and sample temperature to tune the ZnMgO bandgap, rather than varying the photon energy of the excitation laser. The experimental result show that the dependence of LO phonons in Zn1-xMgxO on the Mg composition exhibits one-mode vibration and the buleshift. We have explained the experimental result and known the force in Zn-O bonds. By the detailed theoretical fitting on Loudon's model for the band-to-band transition and a simple atomistic model proposed by Balkanski et al. for the excitonic localization, we demonstrate a pronounced outgoing resonance behavior for the LO phonons. The mechanism of the outgoing resonance can be mainly attributed to the extrinsic Fr?hlich interaction mediated via a localized exciton. We have further found that the localized exciton dominates the outgoing LO phonon resonances in ZnMgO.Finally, through the investigation of temperature dependence of PL spectra, we have clarified that the N-In codoping, compared with the N-doping, leads to the decrement of acceptor binding energy and increment of donor binding energy in ZnO, and also broadens the acceptor level. This result is consistent with the observation of more free hole concentration in the mobility spectra for N-In codoped ZnO. Meanwhile, the introducing of In dopants results in the more free electron concentration in N-In codoped ZnO. In addition we have revealed the different carrier recombination processes in N-In codoped and N-doped p-type ZnO thin films, and confirmed the origin of the deep-level visible emission in undoped ZnO.LEDs based on ZnO p-n homojunciton have been achieved. However, low concentration and mobility of holes in p-type layers greatly limit their light-emitting efficiency. In this dissertation, we will report systematical studies on the structural and optical properties of n-ZnO/MgO/TiN/n+-Si, which was entirely fabricated on Si(111) by PLD. In order to improve the crystal quality and reduce deep-level (DL)defects in the ZnO epi-layer, a low temperature (LT) ZnO buffer layer was employed in the growth process of ZnO epitaxial on the MgO/TiN/Si(111)substrate. Meanwhile we have comparatively investigated the crystal quality and luminescence performance of epitaxial ZnO thin film with or without a LT ZnO buffer layer. It is found that no significant DLEs appear in PL spectroscopy, and the EL output light intensity is enhanced obviously by improving the ZnO crystal quality via employing a LT ZnO buffer layer.This dissertation tightly combines the application of investigation method on semiconductor and the analysis of obtained physical characteristics of these semiconductor materials. On the one hand, we carefully explore how to employ the modern spectroscopy methods to study semiconductor materials; and on the other hand, the obtained physical properties of semiconductors are very important for further studies or applications, which have been deeply analyzed in this dissertation. From the viewpoint of the investigation methodology, we have well combined the theoretical analysis together with the experimental results, that is, the most suitable theories and models are selected to simulate the experimental data, while the experiments are designed based on the requirement and guidance of the theories. Therefore, the experiment data are more reliable and the theoretical analysis is more appropriate. All these achievements have been published in SCI journals.This work is supported in part by the Natural Science Foundation of China under Contract Nos. 10674094 and 10734020, and the National minister of Education Program of IRT0524.