Polarized Micro-Raman Study of GaAs/GaAs(631) Self Assembled Wire...
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= - - = - - = 0 6 3 6 0 3 0 46 1 0 5 9 5 0 3 9 3 0 115 1 0 0 0 0 3 3 0 10 1 ' ' ' d d d d d d R d d d d d d R d d d d R y y x x’= [0,1,-3] y’= [-5,9,3] Scattering geometry Selection rule TO X TO Y TO phonon LO phonon z’(x’,x’)-z’ 0 8|d TO | 2 8 |d TO | 2 28 |d LO | 2 z’(y’,y’)-z’ 5700|d TO | 2 5700|d TO | 2 11400 |d TO | 2 450 |d LO | 2 z’(x’,y’)-z’ z’(y’,x’)-z’ 90|d TO | 2 500|d TO | 2 590 |d TO | 2 235 |d LO | 2 Polarized Micro-Raman Study of GaAs/GaAs(631) Self Assembled Wire-like Arrays Grown by MBE E. Cruz-Hernández 1 , J.S. Rojas-Ramírez 1 , J. Hernández-Rosas 1,3 , M. Ramírez-López 1 , S. Gallardo-Hernández 2 , I. Martínez-Velis 1 y M. López-López 1 1 Physics Department, Centro de Investigación y de Estudios Avanzados del IPN, Apartado Postal 14-740, México, D. F. 07000. 2 AEES, Electrical Engineering Department, Centro de Investigación y de Estudios Avanzados del IPN, Apartado Postal 14-740, México, D. F. 07000. 3 Physics Department, Universidad Autónoma Metropolitana-Iztapalapa, Apartado Postal 55-534, México, D. F. 09340. Introduction In this work, Polarized Micro-Raman (PMR) technique is used to study semiconductor GaAs(631) samples. On the surface of one of the samples we have induced the self-assembling of Wire-like (WR) structures in the growth process by Molecular Beam Epitaxy (MBE) [1]. The other two samples are a GaAs(631) substrate and a GaAs(631) substrate with the oxide desorption process in the MBE chamber with no material deposition. We are looking for the effect of the WRs on the surface of the first sample as compared with the other planar-anisotropic surfaces. Tensor Raman and Selection Rules For a proper interpretation of our results on the (631) plane, we have calculated the Raman tensors (R j ) describing the dipole-allowed scattering by the optical modes in the bulk crystal [2]. From these R j we have obtained the polarization selection rules for backscattering of the perfect planar GaAs(631) crystal. The scattering geometry nomenclature is: Direction of Incident Light (Incident Polarization, Detected Polarization) Direction of Detected Light. Expressed in the x’=[0,1,-3], y’=[5,-9,-3], z’=[6,3,1] coordinate system, we have Polarized Micro-Raman PMR measurements were carried out with a Raman Research System Jobin-Yvon T64000 using the 514.5 nm line of an Ar+ Lexel Laser. This system has an integrated triple spectrometer for optical stability and ultra high resolution to the very accurately study of the position of Raman bands. Using filters, we can control the polarization of the incident light and the detected signal. Results and Discussion The Raman spectra for each sample in all the different configurations are shown in the following graphics. We also show, from these graphics, (a) the dependence between the intensities of the transversal and longitudinal optical phonons (TO and LO), (b) the Raman shift of the TO and LO peaks and, (c) the relative position between the TO and LO peaks. Conclusions We show the PMR spectra obtained under different configurations of the incident and detected light polarization. We have found TO and LO peak shifts caused by the formation of nanostructures on the samples surface. We have shown the phonon confinement in the transversal direction of the superficial WRs. PMR spectra. In the spectra we show the TO and LO peaks position and the configuration of the incident and detected polarization. Also is shown a no polarized Raman spectrum of each sample. The distance between experimental points in the spectra is 0.653 cm-1. We can notice the strong dependence of the LO peak intensity, respect to the TO peak, with the polarization geometry. TO and LO peaks dependence. In the graphic of the I TO /I LO ratios, we can see the desorbed and WR samples follow the predicted behavior from the calculated selection rules. On the other hand, the GaAs(631) substrate do not follows it. We think this behavior is caused by the imperfections in the substrate surface and by the GaAs native oxide layer on it [3]. The graphic of the peaks shift shows a clear shift of both TO and LO peaks with the polarization geometry for the desorbed and WR samples. References [1] E. Cruz-Hernández et al. Journal of Crystal Growth 301-302 (2007) 884-888 [2] Fundamentals of Semiconductors, Peter Y. Yu, M. Cardona, Springer, 1999. [3] A. Guillén-Cervantes, et al. Thin Solid Films 373 (2000) 159. [4] E. Cruz-Hernández et al. Jpn. J. Appl. Phys., Vol 44, No. 51 (2005) L1556-L1559 Acknowledgments This work was partially supported by CONACyT-Mexico. The substrate peaks shift is within the measurement error, there is no clear shift. However, for the grooved (WR) sample, we can see a clear change in the LO frequency for the X’X’ and Y’X’ configurations. As X’, the detected polarization, is in the perpendicular direction of the superficial WRs, we consider this shift is an effect of the phonon confinement in the WRs. For the desorbed sample we have also a peak shift but it does not have a relationship with some specific orientation. We believe this is by the formation of superficial structures in the oxide desorption process [4]. Wired
Transcript of Polarized Micro-Raman Study of GaAs/GaAs(631) Self Assembled Wire...
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Scattering geometry
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z’(y’,y’)-z’ 5700|dTO|2 5700|dTO|2 11400 |dTO|2 450 |dLO|2
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Polarized Micro-Raman Study of GaAs/GaAs(631) Self Assembled Wire-like Arrays Grown by MBE
E. Cruz-Hernández1, J.S. Rojas-Ramírez1, J. Hernández-Rosas1,3, M. Ramírez-López1, S. Gallardo-Hernández2, I. Martínez-Velis1 y M. López-López1
1Physics Department, Centro de Investigación y de Estudios Avanzados del IPN, Apartado Postal 14-740, México, D. F. 07000.2AEES, Electrical Engineering Department, Centro de Investigación y de Estudios Avanzados del IPN, Apartado Postal 14-740, México, D. F. 07000.3Physics Department, Universidad Autónoma Metropolitana-Iztapalapa, Apartado Postal 55-534, México, D. F. 09340.
IntroductionIn this work, Polarized Micro-Raman (PMR) technique is used to study semiconductor GaAs(631) samples. On the surface of one of the samples we have induced the self-assembling of Wire-like (WR) structures in the growth process by Molecular Beam Epitaxy (MBE) [1]. The other two samples are a GaAs(631) substrate and a GaAs(631) substrate with the oxide desorption process in the MBE chamber with no material deposition. We are looking for the effect of the WRs on the surface of the first sample as compared with the other planar-anisotropic surfaces.
Tensor Raman and Selection RulesFor a proper interpretation of our results on the (631) plane, we have calculated the Raman tensors (Rj) describing the dipole-allowed scattering by the optical modes in the bulk crystal [2]. From these Rj we have obtained the polarization selection rules for backscattering of the perfect planar GaAs(631) crystal. The scattering geometry nomenclature is: Direction of Incident Light (Incident Polarization, Detected Polarization) Direction of Detected Light. Expressed in the x’=[0,1,-3], y’=[5,-9,-3], z’=[6,3,1] coordinate system, we have
Polarized Micro-RamanPMR measurements were carried out with a Raman Research System Jobin-Yvon T64000 using the 514.5 nm line of an Ar+ Lexel Laser. This system has an integrated triple spectrometer for optical stability and ultra high resolution to the very accurately study of the position of Raman bands. Using filters, we can control the polarization of the incident light and the detected signal.
Results and DiscussionThe Raman spectra for each sample in all the different configurations are shown in the following graphics. We also show, from these graphics, (a) the dependence between the intensities of the transversal and longitudinal optical phonons (TO and LO), (b) the Raman shift of the TO and LO peaks and, (c) the relative position between the TO and LO peaks.
ConclusionsWe show the PMR spectra obtained under different configurations of the incident and detected light polarization. We have found TO and LO peak shifts caused by the formation of nanostructures on the samples surface. We have shown the phonon confinement in the transversal direction of the superficial WRs.
PMR spectra. In the spectra we show the TO and LO peaks position and the configuration of the incident and detected polarization. Also is shown a no polarized Raman spectrum of each sample. The distance between experimental points in the spectra is 0.653 cm-1. We can notice the strong dependence of the LO peak intensity, respect to the TO peak, with the polarization geometry.
TO and LO peaks dependence. In the graphic of the ITO/ILO ratios, we can see the desorbed and WR samples follow the predicted behavior from the calculated selection rules. On the other hand, the GaAs(631) substrate do not follows it. We think this behavior is caused by the imperfections in the substrate surface and by the GaAs native oxide layer on it [3]. The graphic of the peaks shift shows a clear shift of both TO and LO peaks with the polarization geometry for the desorbed and WR samples.
References [1] E. Cruz-Hernández et al. Journal of Crystal Growth 301-302 (2007) 884-888 [2] Fundamentals of Semiconductors, Peter Y. Yu, M. Cardona, Springer, 1999. [3] A. Guillén-Cervantes, et al. Thin Solid Films 373 (2000) 159.[4] E. Cruz-Hernández et al. Jpn. J. Appl. Phys., Vol 44, No. 51 (2005) L1556-L1559
AcknowledgmentsThis work was partially supported by CONACyT-Mexico.
The substrate peaks shift is within the measurement error, there is no clear shift. However, for the grooved (WR) sample, we can see a clear change in the LO frequency for the X’X’ and Y’X’ configurations. As X’, the detected polarization, is in the perpendicular direction of the superficial WRs, we consider this shift is an effect of the phonon confinement in the WRs. For the desorbed sample we have also a peak shift but it does not have a relationship with some specific orientation. We believe this is by the formation of superficial structures in the oxide desorption process [4].
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