Magnetotransmission spectroscopy, the optical absorption measurement using circularly polarized light in the range
from far infrared to near ultraviolet, is a direct method to study the energy structure of diluted magnetic semiconductors.
In this paper, the magnetotransmission measurement is performed on the ferromagnetic Mn-doped ZnO films. The
splitting between two circularly polarized light absorption edge is up to 10 meV under external magnetic field of 0.8 T at
room temperature. The splitting is closely follows the magnetization of the films, as measured using Vibrating Sample
Magnetometer. The observed ferromagnetic-type splitting of absorption edge is explained by antiferromagnetic p-d
exchange interaction.
Effect of Al-N codoping ratio on the conducting and optical properties of ZnO films deposited by helicon wave plasma
assisted radio frequency magnetron sputtering under various N2 gas flow is investigated. Hall measurements show that p-type
ZnO thin films have been achieved with proper N2 flow rate. X-ray diffraction patterns indicate that all the films are
highly c-axis oriented. Room temperature photoluminescence spectra show a strong near-band-edge emission. With
increasing N doping, the intensity of the emission behaves an increased and then decreased trend while the full width at
half maximum is narrowed and then widened. In addition, photoluminescence spectrum at 77 K in the p-type ZnO film
with the highest hole concentration show a much stronger peak near 3.32 eV (due to N related neutral acceptor bound
excitons), than at 3.36 eV (neutral donor bound excitons), and the acceptor energy level is estimated to be 186 meV.
Thermal annealing of amorphous SiC films deposited by pulsed laser ablation is performed at different temperature of 900-1050°C in vacuum condition. The structural and optical properties of the obtained films have been investigated by Micro-Raman scattering, UV- VIS transmission, and atomic force microscopy (AFM). It has been observed that the Raman bands related to SiC TO and LO modes appear and gradually shift to higher energy with increasing the annealing
temperature, indicating that the crystallization of SiC occurs in the post-annealed films and their crystallinity increases. AFM results show that the post-annealed film is composed of compact nanoparticles and presents a rougher surface with respect to the as-deposited film. Optical band gaps deduced from UV-VIS transmission spectra are continuously increased from 1.90 eV for as deposited films to 2.45 eV of the annealed films at temperature of 1050°C. The formation of SiC nanocrystallines and the improvement of crystallinity can account for this blue-shift effect of the optical band gap.
Hydrogenated amorphous silicon nitride (a-SiNx:H) thin films are deposited by helicon wave plasma chemical vapor deposition technique. The structural and photoluminescence properties of these films have been characterized by X-ray photoelectron spectroscopy (XPS), Photoluminescence (PL) and ultraviolet-visible (UV-VIS) spectroscopy. It is shown that the silicon atom bonds exist in the Si-Si and Si-N configurations and the amorphous silicon regions appear separately in the Si-rich a-SiNx films. All the PL spectra of the deposited films manifest itself as several interference peaks superposed on an energy-dependent Gaussian distributed band. The PL and absorption results of the deposited films with different nitrogen content support that the luminescence of the Si-rich a-SiNx:H films is related to the photo-excited carriers radiation process in the separated amorphous silicon potential well region, while the blue shift of PL main peaks and the enlargement of PL intensity with increase nitrogen content are ascribed to the size reduction of amorphous silicon separated regions and the enhancement of confinement effect.
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