Keywords : semiconductor

Tunneling Effect Of Photon-assisted AZO/SiOx/n-Si Heterojunction Device At Reverse Bias

H. W. Du; J. Yang; F. Xu; L. Zhao; Z. Q. Ma

Advanced Materials Letters, 2016, Volume 7, Issue 5, Pages 349-352
DOI: 10.5185/amlett.2016.6169

Physical asymmetrical Metal / AZO / SiOx / n-Si / Metal devices in semiconductor-insulator-semiconductor (A-SIS) framework were investigated for their anormaly current-voltage characteristics under light irradiation. The devices showed a normal rectifying character in dark but manifested a peculiar current-voltage feature at reverse bias under illumination. Considering the change of energy band structure at the reverse electric field, it was found that the transport of electrons was mainly dominated by the thermionic emission and quantum tunneling at low voltage. With the increase of the reverse bias, the electrons were able to tunnel through the reduced barrier of ultra-thin SiOx layer (<1nm) and an effective triangle-like barrier of silicon. An appropriate simulation of the J-V relationship demonstrated that the photons acting as the assisted part magnified the reverse current density, and the thickness of SiOx layer managed the amount of the reverse saturation current. 

Effect Of Diffusion Parameters On The Efficiency Of C-Si Solar Cell

Vineet Kumar Singh; Jampana Nagaraju

Advanced Materials Letters, 2015, Volume 6, Issue 7, Pages 600-606
DOI: 10.5185/amlett.2015.5616

This paper presents the effect of emitter thickness and post-annealing process on the conversion efficiency of crystalline silicon (c-Si) solar cells. Diffusion parameters like pre-deposition temperature, drive-in temperature, and process duration assist to control the emitter thickness and inturn improves the conversion efficiency of the solar cells. It is observed that shallower emitter cells have higher conversion efficiency of 10.81% than deeper emitter cells of 7.62%. Post-annealing process at 700 °C for 60 minutes boosts the efficiency of shallower emitter cell from 10.81% to 12.06%. Dark current-voltage characteristics authenticate the formation of p-n junction and also elucidate the presence of recombination saturation current along with diffusion saturation current. Illuminated and dark current-voltage characteristics further provide the evidence that post-annealing process during phosphorus diffusion reduces the trap density and thus the recombination saturation current, which helps to improve the efficiency. The combination of a shallower emitter with post-annealing process provides an excellent approach to enhance the solar cell efficiency.

Spectroscopy And Structural Study On CdSe Thin Films Deposited By Chemical Bath Deposition

M. P. Deshpande; Nitya Garg; Sandip V. Bhatt; Pallavi Sakariya; S. H. Chaki

Advanced Materials Letters, 2013, Volume 4, Issue 11, Pages 869-874
DOI: 10.5185/amlett.2013.4467

Cadmium selenide (CdSe) thin films were prepared by chemical bath deposition technique on glass substrates using cadmium acetate dihydrate as a source of Cd 2+ ions, and sodium selenosulphate as a source of Se 2- ions respectively. Triethanolamine and ammonia were used as complexing and pH controlling agent. Films were deposited at different bath temperatures ranging from room temperature to 80 o C while the pH value was kept constant around 10.50 ±0.10. We determined elemental composition of deposited film by X-ray photoelectron spectroscopy. Optical properties of films deposited at different bath temperatures are studied by absorption spectra and parameters like thickness, band gap and absorption coefficient were calculated from the optical transmission spectra. The optical spectra showed a small blue shift and the band gap was found to be greater than the bulk phase. Raman measurements performed at room temperature using Helium-neon laser and Argon laser confirmed the presence of longitudinal optical phonon modes. The selected area electron diffraction pattern for CdSe thin films indicated that they are having mixed nature i.e. both single crystalline and polycrystalline nature with planes of diffraction rings corresponding to cubic structure of CdSe respectively.

Facile Fabrication Of Uniform Silica Films With Highly Luminescent Hydrophobic QDs Through Direct Phase Transfer

Zhongsen Yang; Guangjun Zhou

Advanced Materials Letters, 2012, Volume 3, Issue 1, Pages 2-7
DOI: 10.5185/amlett.2011.6273

Hydrophobic CdSe/ZnS quantum dots (QDs) were embedded in a transparent functional silica film with thickness of 10-15 µm using a sol-gel method. Namely, the QDs were prepared through an organic synthesis using hexadecylamine as a capping agent. When partially hydrolyzed 3-aminopropyltrimethoxysilane (APS) sol was mixed with a toluene solution of the QDs, the ligand exchange occurred. With subsequent addition of pure H2O, the QDs were transferred into APS sol accompanied with a phase separation. The APS sol with the QDs was condensed to adjust its’ viscosity by the evaporation of solvents at room temperature. After that, functional SiO2 films with tunable QD concentrations and high photoluminescence (PL) efficiency were fabricated by a spin-coating strategy using the condensed APS sol with the QDs. The absorbance at first absorption peak of the QDs revealed a liner increase against the QD concentrations in these films. The PL peak wavelength and full width at half maximum of PL spectra of the QDs in these films remained unchange compared with their initial values in toluene. The QDs were mono-dispersed in these films according to transmission electron microscopy observation. Due to unique properties, these films are utilizable for further applications in optical and electronic devices.

Solid State Thermochromic Materials

Pragna Kiria; Geoff Hyett; Russell Binions

Advanced Materials Letters, 2010, Volume 1, Issue 2, Pages 86-105
DOI: 10.5185/amlett.2010.8147

Solid-state thermochromic materials undergo semiconductor to metal transitions at a ‘critical temperature’, Tc. This review begins by describing the phenomenon of thermochromism, whereby the optical properties of a material change reversibly as a result of a change in temperature. The various different types of thermochromism will be introduced with a focus on the thermochromism exhibited by solid-state materials. The fundamental chemical principles that describe the electronic structure and properties of solids, and the chronological developments in the theory behind the thermochromic transitions (such as, the effects of electron-electron interactions and structural phase changes due to lattice distortions) that led to the discovery of the semiconductor-to-metal transition, are presented. An extensive discussion of vanadium and titanium oxides is presented with a particular focus on vanadium (IV) oxide since its transition temperature is closest to room temperature. Observations and current understanding of the nature of the semiconductor-to-metal transition exhibited by these materials is detailed. The possibility of fine-tuning the transition temperature by introducing various dopants into the vanadium (IV) oxide lattice is examined and the effects of dopant charge and size is examined. Solid-state thermochromic materials may be exploited in areas such as microelectronics, data storage, or intelligent architectural glazing, thus are required to be synthesised as thin films for use in such applications. The numerous synthetic techniques (PVD, sol-gel method, PLD, CVD, APCVD and AACVD), for making metal oxide thermochromic thin films are described in reference to the production of vanadium (IV) oxide and compared. Finally rare earth nickelates exhibiting thermochromism are described.