جستجوی مقالات مرتبط با کلیدواژه « quantum efficiency » در نشریات گروه « فیزیک »

Detection of weak signals is one of the important issues in spectroscopy. The most important parameters of this field is the signal to noise ratio, which has a significant effect on the accuracy of the final data. In this regard, one of the most successful methods to increase the signal-to-noise ratio is to apply the intensity modulation method. In this method, first, the intensity of the initial signal is modulated, and after entering in the spectrometer, it is demodulated and amplified by a lock-in amplifier and eventually, the desired signal is recovered from various noises. The simulation allows the user to examine and optimize the related parameters for different initial conditions. The present article is dedicated to designing a lock-in amplifier by applying a LabVIEW graphical programming language.

In the present study, we introduce a concept to generate the spin-polarized current in armchair transition metal dichalcogenide nanoribbons (TMDNs) by  using light irradiation. For simulating the opto-spin current, we use electron-photon interaction in non-equilibrium Green's function methods. Because of the intrinsic spin-orbit coupling, light irradiation produces spin-photocurrent in TMDNs without applying any external magnetic element. Moreover, transverse electric field modifies the magnitude and position of optical absorption peaks, as well as the magnitude of the spin-photocurrent. Finally, the fully spin-polarized photocurrent, the high quantum efficiency with a maximum of approximately 50%, the wide-wavelength-range operation from ultraviolet to infrared and optical spin-filtering effects are tunable with transverse electric field indicate the high performance of this spin-photodetector based on armchair TMDNs, thereby paving the way  toward the improved design and performance of this photodetector in spin-optoelectronics.

In this study, CdS films prepared using the technique of pyrolysis spray at the glass and Si wafer with a thickness of 300 nm using Cadmium Acetate Cd (CH3COO)2·2H2O with purity of 99.6% and Thiourea (CS(NH2)2) with purity 99.6%. These compounds are used as the sourced materials of Cd+2 and S-2 ions, respectively for the CdS films formation. The films were annealed at different temperatures (400, 500, and 600 0C), then the effect of annealing on its properties was studied. The high-quality films were obtained as evident using XRD analysis. X-ray diffraction analysis for all CdS films was polycrystalline with cubic and hexagonal wurtzite structure with preferential orientation in the H (002) and C (111) direction. It is difficult to distinguish between them, after high-temperature process from 400 0C to 6000C, new peaks of the hexagonal structure appeared. This phenomenon was thought to be the phase change of CdS thin film by heat treatment as well as the increasing of intensity of H (002) and decreases in full width at half maxima (FWHM) the grains size with annealing. The CdS photodetector and the spectral response of CdS/Si junction was studied. The maximum value of responsivity occurred at a wavelength of 500 nm to 560 nm. The maximum values of D* and η at Ta equal to 500 0C. Whereas, they increase and shift to higher wavelength with the increase of Ta. It has been observed that the best spectral response occurs when the annealing temperature equal to 500 0C, therefore, is essential to say that this value of Ta was the optimum condition for prepared CdS photoconductive detector.

In this work, oscillator strength and quantum efficiency of new spherical GaN/AlGaN quantum dot was investigated. In order to obtain these parameters, at first, Schrödinger equation is solved in GaN/AlGaN spherical coordinate system in effective mass approximation, and energy level, wave function and transition matrix element of the parameter are obtained. The results show that oscillator strength decreases with increase of mol fraction and dot size. This effect is more obvious for high mol fractions. With increasing mol fraction of defect, the peak of quantum efficiency shows blue shift. Increasing the radius of core and shell causes the red shift of quantum efficiency peak. The red and blue shifts can be very useful in tunning and controling the detector wavelenght range

In this article, the operations of heterojunction silicon solar cells were investigated theoretically. The studied structure is TCO/ a-SiC (P)/ GaP (i)/ a-Si (n)/ a-Si (n)/ metal. In this study instead of using conventional structure, which uses an amorphous intrinsic layer, a GaP (Gallium Phosphate) layer is used as intrinsic buffer layer. Different models of this solar cell structure were simulated. The effect of various parameters such as work functions of front and back contacts, emitter and n-type amorous silicon layer carrier densities, emitter band gap, GaP buffer layer thickness, current- voltage curves and quantum efficiency has been studied. The optimum values for above mentioned quantities are presented based on the study results. Moreover the band structure of different cases is plotted. The results show that using a GaP intrinsic layer with 2.26 ev band gap and 1 micrometer thick, leads to the highest efficiency around 21.13% with Voc=1.52 V, Jsc=16.58 mA.cm-2 and FF= 84 %.