Investigation of proton damage in III-V semiconductors by optical spectroscopy

We studied the damage produced by 2MeV proton radiation on epitaxially grown InGaP/GaAs structure by means of spatially resolved Raman and photoluminescence (PL) spectroscopy. The irradiation was performed parallel to the sample surface in order to determine the proton penetration range in both compounds. An increase in the intensity of longitudinal optical phonons and a decrease in the luminescence were observed. We associate these changes with the creation of defects in the damaged region, also responsible for the observed change of the carrier concentration in the GaAs layer, determined by the shift of the phonon-plasmon coupled mode frequency. From the spatially resolved profile of the PL and phonon intensities, we obtained the proton range in both materials and we compared them with stopping and range of ions in matter simulations. The comparison between the experimentally obtained proton range and simulations shows a very good agreement for GaAs but a discrepancy of 20% for InGaP. This discrepancy can be explained in terms of limitations of the model to simulate the electronic orbitals and bonding structure of the simulated compound. In order to overcome this limitation, we propose an increase in 40% in the electronic stopping power for InGaP.This work was supported by BEC.AR FUNDACION YPF-CONICET 2013 (Argentina) and DFG within Grant No. SFB 787. ARG thanks the Spanish Ministry of Economy and Competitiveness (MINECO) for its support through Grant No. SEV-2015-0496 in the framework of the Spanish Severo Ochoa Centre of Excellence program.Peer reviewe

Molecular nitrogen acceptors in ZnO nanowires induced by nitrogen plasma annealing

©2015 American Physical Society. X-ray absorption near-edge spectroscopy, photoluminescence, cathodoluminescence, and Raman spectroscopy have been used to investigate the chemical states of nitrogen dopants in ZnO nanowires. It is found that nitrogen exists in multiple states: NO,NZn, and loosely bound N2 molecule. The results establish a direct link between a donor-acceptor pair emission at 3.232 eV and the concentration of loosely bound N2. This work confirms that N2 at Zn site is a potential candidate for producing a shallow acceptor state in N-doped ZnO as theoretically predicted by Lambrecht and Boonchun [Phys. Rev. B 87, 195207 (2013)10.1103/PhysRevB.87.195207]. Additionally, shallow acceptor states arising from NO complexes have been ruled out in this paper

Elastic properties of crystalline-amorphous core-shell silicon nanowires

The pressure behavior of Raman frequencies and line widths of crystalline core-amorphous shell silicon nanowires (SiNWs) with two different core-to-shell ratio thicknesses was studied at pressures up to 8 GPa. The obtained isothermal compressibility (bulk modulus) of SiNWs with a core-to-shell ratio of about 1.8 is ∼20% higher (lower) than reported values for bulk Si. For SiNWs with smaller core-to-shell ratios, a plastic deformation of the shell was observed together with a strain relaxation. A significant increase in the full width at half-maximum of the Raman LTO-peak due to phonon decay was used to determine the critical pressure at which LTO-phonons decay into LO + TA phonons. Our results reveal that this critical pressure in strained core-shell SiNWs (∼4 GPa) is different from the reported value for bulk Si (∼7 GPa), whereas no change is observed for relaxed core-shell SiNWs. © 2013 American Chemical Society

Chemical, vibrational and optical signatures of nitrogen in ZnO nanowires

© 2016 Elsevier Ltd ZnO nanowires with various concentrations of nitrogen molecules have been fabricated by remote plasma annealing. X-ray absorption near-edge spectroscopy (XANES) reveals that nitrogen exists mainly in two chemical states: atomic nitrogen substituting oxygen (NO) and molecular nitrogen (N2) weakly bound to the ZnO lattice; the latter state increases substantially with prolonged plasma time. Cathodoluminescence microanalysis of individual nanowires reveals a broad emission band at 3.24 eV at 10 K, attributable to the recombination of a shallow donor and a N2 acceptor state. The Raman modes at 547 and 580 cm−1 from the N-doped nanowires are found to rise in proportion to the N2 concentration, indicating they are related to N2 molecules or defects caused by the incorporation of N2 in the nanowires

Elastic properties of crystalline-amorphous core-shell silicon nanowires

The pressure behavior of Raman frequencies and line widths of crystalline core-amorphous shell silicon nanowires (SiNWs) with two different core-to-shell ratio thicknesses was studied at pressures up to 8 GPa. The obtained isothermal compressibility (bulk modulus) of SiNWs with a core-to-shell ratio of about 1.8 is ∼20% higher (lower) than reported values for bulk Si. For SiNWs with smaller core-to-shell ratios, a plastic deformation of the shell was observed together with a strain relaxation. A significant increase in the full width at half-maximum of the Raman LTO-peak due to phonon decay was used to determine the critical pressure at which LTO-phonons decay into LO + TA phonons. Our results reveal that this critical pressure in strained core-shell SiNWs (∼4 GPa) is different from the reported value for bulk Si (∼7 GPa), whereas no change is observed for relaxed core-shell SiNWs. © 2013 American Chemical Society

Effects of annealing on optical and structural properties of zinc oxide nanocrystals

& Co. KGaA, Weinheim. The optical and vibrational properties of zinc oxide nanocrystals (ZnO NCs), grown by chemical precipitation method, were investigated following thermal annealing treatments in oxygen, argon, and zinc vapors at temperatures up to 900{ring operator}C. Raman scattering and photoluminescence techniques were utilized to show the effect of temperature annealing in various environments on optical and structural properties of ZnO NCs, referring them to the reduction and increase of certain intrinsic defect concentrations. The experimental results are complemented by density functional theory calculations for understanding the correlation between Raman modes induced with different annealing procedures and certain intrinsic point defects. © 2015 WILEY-VCH Verlag Gmb