II-VI Semiconductor Materials Research Articles

Optical Characterization of Ferric-Doped ZnO Thin Film Deposited By Chemical Bath Deposition Method

Fe-doped ZnO holds numerous potential uses in devices such as UV light emitters, piezoelectric transducers, transparent electronics in solar cells, and bright windows as an II-VI semiconductor material. This study looked into the band gap, surface characteristics, optical transmittance, and absorbance of ZnO thin films with Fe doping in different pH conditions such as 8, 9, and 10. The films were prepared using the chemical bath deposition (CBD) method at 350 °C on a glass substrate. The samples were characterized using UV-visible spectroscopy and scanning electron microscopy (SEM). The SEM images of the undoped samples exhibited a lack of cracks, but the doped samples displayed visible cracks due to the presence of Fe in the films. ZnO thin-film surface shape is altered by pH and Fe doping variations. There is a tendency for the films' visual transmission to decrease when the pH rises. The absorbance for all samples increases in the UV and declines in the visible. Fe doping causes the optical band gap Eg to drop. The band gap of both doped and undoped samples reduces when pH rises.

Creating metal saturated growth in MOCVD for CdTe solar cells

Determining the thermodynamic conditions in MOCVD growth of II-VI semiconductor materials is not as straightforward as in III-V growth where Group V hydrides are generally used. This paper establishes a technique, using in situ laser reflectometry, to ensure that the thermodynamic equilibrium is under metal saturated growth. This has been applied to the arsenic doping of CdTe solar cells where it was shown that increasing the II/VI precursor ratio resulted in an increase in As dopant incorporation. The growth kinetics were determined by the diisopropyl tellurium (DIPTe) concentration for II/VI precursor ratios above 2. A method is presented where the change in II/VI precursor ratio can be predicted for different positions in a horizontal MOCVD chamber that has, in turn, enabled variation in NA and the solar cell open circuit voltage (Voc) to be determined as a function of the II/VI precursor ratio. This gives new insight to the thermodynamic drivers in MOCVD growth for improved solar cell Voc and is a method that could be applied to MOCVD of other II-VI semiconductors.

Fabrication and properties of non-balance electric bridge gas sensor based on a single Sb doped ZnO microwire

Zinc oxide (ZnO) is a wide direct band gap (3.37 eV) II-VI semiconductor material with a wide range of applications in light emitting devices, solar cells, field emission devices, gas sensors, etc. Over the past decades, metal oxide semiconductors have been investigated extensively for sensing various types of vapors and toxic gases. Among the various metal oxides for gas sensing applications, ZnO is one of the potential materials for high response, stability and sensitivity to volatile organic gases. At present, the ZnO-based gas sensor has a relatively high operating temperature. However, the stability and lifetime of gas sensors operating under high temperature conditions with a long term will be greatly reduced. In addition, the power consumption of gas sensors is also significantly increased. Furthermore, there can exist the potential of explosion when gas sensors are used to detect the flammable gases at high temperature. Therefore, it is necessary to improve the sensing properties and reduce the operating temperature of gas sensors. In this paper, ultra-long, large-sized Sb doped ZnO microwires are successfully prepared by using chemical vapor deposition. The gas sensor is based on the principle of non-balance electric bridge, and a single Sb doped ZnO microwire is used as a bridge arm <i>R</i><sub>4</sub> of non-balance electric bridge to produce a gas sensor that can work at room temperature. The results show that the response-recovery curves of sensors at the acetone and ethanol concentrations of 20 ppm, 50 ppm, 100 ppm and 200 ppm (1 ppm = 10<sup>–6</sup>) are rectangular at room temperature, and have stable current values in air and measured gas, and the response value of the device gradually increases with gas concentration increasing. Furthermore, the detection of acetone and ethanol gas reveal that the device has better selectivity for acetone gas. The response of the gas sensor to 200 ppm acetone is about 243%, with response and recovery time of 0.2 s and 0.3 s, respectively. Compared with the traditional resistive gas sensor, this non-balanced electric bridge sensor has high response, fast response and recovery time. In addition, the sensing mechanism of the device is also studied.

Гидрохимический синтез халькогенидов металлов. Часть 41. Гидрохимическое осаждение тонких пленок селенида кадмия селеносульфатом натрия

The group II-VI semiconductor materials including Cadmium Selenide (CdSe) thin films are widely used in many fields of science and technology, in particular in optoelectronics, nanoelectronics and solar energy. Chemical bath deposition (CBD) represents the simplest and the most available technique for deposition of semiconducting layers. CBD is characterized by deletion of toxic gaseous precursors, operation at low temperature and using of inexpensive equipment. The ionic equilibriums in reaction mixture «CdCl2 – L − Na2SeSO3» (L− NH4OH or Na3C6H5¬O7 or mixture of NH4OH and Na3C6H5¬O7 ) were calculated in present work. The prevailing cadmium complex compounds were determined in appropriate for CBD of cadmium selenide films pH range. The main complex compounds inhibiting fast formation of cadmium selenide are Cd(OH)Cit^(2-) complex (in citrat- and ammonia-citrat mixtures) and 〖Cd(NH_3)〗_5^(2+) complex (in ammonia mixture). Also the boundary conditions of forming CdSe and Cd(OH)2 in reaction mixture were determined by thermodynamic calculation based on crystallization factor to estimate the formation conditions of main (CdSe) and impurity (Cd(OH)2) phases. The results of the calculations show that the solid phase of cadmium selenide is possible to form in pH range from 10 to 14. CdSe films were grown by chemical bath deposition on glass substrates at a temperature of 353 K. The thickness of films ranges from 100 to 220 nm. The grain size of films is about 30 nm which was determined by electron microscopic investigations. The elemental composition of cadmium selenide was defined by energy dispersive analysis; the ratio of cadmium and selenium is 1.03 : 1.16. The conductivity of n-type was determined by the sign of thermoelectromotive force.

Maskless Photoelectrochemical Fabrication of Anisotropic Three-Dimensional Nanostructured Semiconductors

Binary and ternary IV-VI and II-VI semiconductor materials were photoelectrochemically deposited from aqueous precursors, yielding highly periodic nanostructured films over macroscopic square centimeter areas despite the absence of any templating agents or lithographic steps. Electro-/chemical modification was performed following deposition to tune the elemental stoichiometry of the deposits without a concomitant loss in structure fidelity nor crystallinity. The morphology of these features was controlled by the optical inputs to the deposition: extremely anisotropic lamellar-type features formed spontaneously under the presence of linearly polarized light and the periodicity of the features scaled with illumination wavelength. The deposition process was simulated using a two-step iterative model which included a finite-difference time domain method to model light absorption and a Monte Carlo method to model mass addition; these simulations matched the experimentally observed morphologies. This approach offers a method by which highly nanostructured materials that are of interest for photon-harvesting applications can be deposited in a manner that allows for self-optimization in order to maximize light absorption. This work demonstrates that photoelectrochemical deposition can be utilized to provide rapid, template-free fabrication of 3D semiconductor nanopatterns over macroscale areas for a variety of material systems. Extension of this technique to group IV materials is underway.

Size-dependent bandgap and particle size distribution of colloidal semiconductor nanocrystals.

A new analytical expression for the size-dependent bandgap of colloidal semiconductor nanocrystals is proposed within the framework of the finite-depth square-well effective mass approximation in order to provide a quantitative description of the quantum confinement effect. This allows one to convert optical spectroscopic data (photoluminescence spectrum and absorbance edge) into accurate estimates for the particle size distributions of colloidal systems even if the traditional effective mass model is expected to fail, which occurs typically for very small particles belonging to the so-called strong confinement limit. By applying the reported theoretical methodologies to CdTe nanocrystals synthesized through wet chemical routes, size distributions are inferred and compared directly to those obtained from atomic force microscopy and transmission electron microscopy. This analysis can be used as a complementary tool for the characterization of nanocrystal samples of many other systems such as the II-VI and III-V semiconductor materials.

The preparation of anisotropic hybrid nanostructures based on CdSe and CdS by the ligand combination method.

CdSe and CdS nanoparticles (NPs) are type I II-VI semiconductor materials with excellent optical properties. Usually various shapes of these NPs show a strong emission only from a CdSe or CdS single domain, while the emission from a CdSe core combined with a CdS shell is effectively suppressed due to the ultrafast hole relaxation from the CdS shell into the CdSe core. Therefore, the design and synthesis of heteronanostructures based on CdSe or CdS is of paramount importance in designing the ways of integrating these useful semiconductor materials into complex hybrid structures. Here we demonstrate the ligand-combination inducing growth method to prepare anisotropic core-shell (semiconductor-semiconductor) heteronanostructures, as well as anisotropic Au-semiconductor heteronanostructures. The NPs' anisotropic shape was confirmed by tilting a grid in TEM and their elemental composition was ascertained using EDX mapping in STEM mode. Furthermore, the photoluminescence excitation spectra were studied showing potential applications based on their unique optical properties. We believe that the mechanism investigation, the synthetic control, the obtained novel hybrid nanostructures and their optical properties will open doors to future studies on heterostructures based on semiconductors.

Mid-Infrared Intersubband Absorption from p-Ge Quantum Wells Grown on Si Substrates

There are many applications in the mid-infrared part of the electromagnetic spectrum which include thermal imaging [1] and the unique identification of molecules through absorption spectroscopy [2]. For all these applications, sources of mid-infrared light and photodetectors are key to enable any application. III-V and II-VI semiconductor materials have dominated over the last decades with both interband and intersubband emission and/or absorption devices [1-3] but there is now significant interest in developing technology on silicon substrates to enable far cheaper systems for mass market applications in environmental sensing, personalised healthcare and security. SiGe quantum well (QW) intersubband photodetectors (QWIPs) have previously been demonstrated [4] but the number of QWs was limited by the SiGe critical thickness thereby limiting performance. Now Ge QWs have the potential to improve this performance significantly in the mid-infrared and the number of QWs can be increased using strain symmetrisation of the QWs and barriers to allow improved absorption in the longer wavelength mid-infrared. Here we demonstrate strain symmetrized growth of 500 periods of Ge QWs with Si0.5Ge0.5 barriers on Si0.2Ge0.8 virtual substrates grown on top of (001) Si. The samples were grown by low energy plasma enhanced chemical vapour deposition. Transmission electron microscopy, Raman spectroscopy and x-ray diffraction were used to characterize the heterolayer thicknesses, Ge contents, strain and defects. The layers demonstrate excellent quality with low defect densities. Three samples with QW thicknesses (barrier thicknesses) of 5.4 ± 0.4 nm (3.5 ± 0.4 nm), 8.1 ± 0.5 nm (5.2 ± 0.6 nm) and 9.2 ± 0.6 nm (6.1 ± 0.6 nm) have been fully characterized by Fourier transform infrared spectroscopy (FTIR) to understand the potential for mid-infrared QWIPs. An 8-band k.p modelling tool has been used to understand the results. For the lowest QW width, only z-polarised absorption is observed at ~ 7 µm wavelength from the light hole 1 (LH1) to LH2 transition. Despite surface-normal illumination, the z-polarized transition is observed since the heterolayers and substrate will scatter some of the light into the z-polarized mode. For the thicker QWs, only xy-polarized (surface normal) absorption is measured with absorption peaks centred at 7.5 µm and 7.8 µm corresponding to the heavy hole 1 (HH1) to LH2 transition. Temperature dependent FTIR measurements demonstrate virtually no shift in the wavelength of absorption with temperature as is typical for intersubband transitions. Photoluminescence (PL) demonstrates a completely different behavior to the absorption due to the population of states being different through the heating of the samples by the 532 nm PL laser. We will demonstrate how to design QWIPs using a HH1 to LH bound-to-continuum transitions that will enable surface-normal QWIPs to be designed with large pixel numbers and produced cheaply on a silicon substrate using any silicon foundry with SiGe growth capability. The research leading to these results has received funding from the European Unions Seventh Framework Programme under grant agreement no. 613055 and U.K. EPSRC (Project no. EP/N003225/1). [1] A. Rogalski, J. Appl. Phys. 93, 4355 (2003) [2] L. Baldassarre, E. Sakat, J. Frigerio, A. Samarelli, K. Gallacher, E. Calandrini, G. Isella, D. J. Paul, M. Ortolani, and P. Biagioni, Nano Lett. 15, 7225 (2015) [3] A. Rogalski, Infrared Phys. Technol. 38, 295 (1997). [4] R. P. G. Karunasiri, J. S. Park, Y. J. Mii, and K. L. Wang, Appl. Phys. Lett. 57, 2585 (1990) Figure 1

Microbial toxicity of ionic species leached from the II-VI semiconductor materials, cadmium telluride (CdTe) and cadmium selenide (CdSe)

This work investigated the microbial toxicity of soluble species that can potentially be leached from the II-VI semiconductor materials, cadmium telluride and cadmium selenide. The soluble ions tested included: cadmium, selenite, selenate, tellurite, and tellurate. Their toxicity towards the acetoclastic and hydrogen-consuming trophic groups in a methanogenic consortium as well as towards a bioluminescent marine bacterium, Aliivibrio fischeri (Microtox® test), was assessed. The acetoclastic methanogenic activity was the most affected as evidenced by the low 50% inhibiting concentrations (IC50) values obtained of 8.6 mg L−1 for both cadmium and tellurite, 10.2 mg L−1 for tellurate, and 24.1 mg L−1 for selenite. Both tellurium oxyanions caused a strong inhibition of acetoclastic methanogenesis at low concentrations, each additional increment in concentration provided progressively less inhibition increase. In the case of the hydrogenotrophic methanogenesis, cadmium followed by selenite caused the greatest inhibition with IC50 values of 2.9 and 18.0 mg L−1, respectively. Tellurite caused a moderate effect as evidenced by a 36.8% inhibition of the methanogenic activity at the highest concentration tested, and a very mild effect of tellurate was observed. Microtox® analyses showed a noteworthy inhibition of cadmium, selenite, and tellurite with 50% loss in bioluminescence after 30 min of exposure of 5.5, 171.1, and 458.6 mg L−1, respectively. These results suggest that the leaching of cadmium, tellurium and selenium ions from semiconductor materials can potentially cause microbial toxicity.

Density functional theory based tight binding study on theoretical prediction of low-density nanoporous phases ZnO semiconductor materials

Polymorphs or phases - different inorganic solids structures of the same composition usually have widely differing properties and applications, thereby synthesizing or predicting new classes of polymorphs for a certain compound is of great significance and has been gaining considerable interest. Herein, we perform a density functional theory based tight binding (DFTB) study on theoretical prediction of several new phases series of II-VI semiconductor material ZnO nanoporous phases from their bottom-up building blocks. Among these, three phases are reported for the first time, which could greatly expand the family of II- VI compound nanoporous phases. We also show that all these generally can be categorized similarly to the aluminosilicate zeolites inorganic open-framework materials. The hollow cage structure of the corresponding building block ZnkOk (k= 9, 12, 16) is well preserved in all of them, which leads to their low-density nanoporous and high flexibility. Additionally the electronic wide-energy gap of the individual ZnkOk is also retained. Our study reveals that they are all semiconductor materials with a large band gap. Further, this study is likely to be the common for II-VI semiconductor compounds and will be helpful for extending their range of properties and applications.

Organic-inorganic perovskite plasmonic nanowire lasers with a low threshold and a good thermal stability.

Plasmonic nanolasers have ushered in a paradigm of deep sub-wavelength coherent optical sources with ultrafast dynamics that exploit the strong confinement capabilities of metals. Although these devices are usually associated with higher thresholds due to absorption in metals, the high gain inorganic II-VI and III-V semiconductor materials have allowed the realization of plasmonic nanolasers operating under ambient conditions. In this work, we introduce single-crystalline lead halide perovskite (CH3NH3PbI3) nanowires as an organic-inorganic semiconducting gain material to the plasmonic laser community. We demonstrate plasmonic laser action using a hybrid geometry whereby the perovskite nanowires are placed on a silver substrate with an insulating spacer layer. We report relatively low threshold operation under ambient conditions (13.5 μJ cm-2), and the devices work well even at temperatures up to 43.6 °C. The demonstration highlights the high optical gain achievable in perovskite materials and thus provides a solution to high gain materials for plasmonic devices.

A transferable force field for CdS-CdSe-PbS-PbSe solid systems.

A transferable force field for the PbSe-CdSe solid system using the partially charged rigid ion model has been successfully developed and was used to study the cation exchange in PbSe-CdSe heteronanocrystals [A. O. Yalcin et al., "Atomic resolution monitoring of cation exchange in CdSe-PbSe heteronanocrystals during epitaxial solid-solid-vapor growth," Nano Lett. 14, 3661-3667 (2014)]. In this work, we extend this force field by including another two important binary semiconductors, PbS and CdS, and provide detailed information on the validation of this force field. The parameterization combines Bader charge analysis, empirical fitting, and ab initio energy surface fitting. When compared with experimental data and density functional theory calculations, it is shown that a wide range of physical properties of bulk PbS, PbSe, CdS, CdSe, and their mixed phases can be accurately reproduced using this force field. The choice of functional forms and parameterization strategy is demonstrated to be rational and effective. This transferable force field can be used in various studies on II-VI and IV-VI semiconductor materials consisting of CdS, CdSe, PbS, and PbSe. Here, we demonstrate the applicability of the force field model by molecular dynamics simulations whereby transformations are initiated by cation exchange.

Nanocrystals Encapsulated in SiO<SUB>2</SUB> Particles: Silanization and Homogenous Coating for Bio Applications

Sol-gel procedures have been developed to encapsulate inorganic nanocrystals including metallic Au and II-VI semiconductor materials (CdSe/Cd(1-x)Zn(x)S) in SiO2 particles by using tetraethyl orthosilicate. The key strategy was the control of a sol-gel procedure. The anisotropic deposition of SiO2 monomers occurs because well-developed crystal facets having different affinity to SiO2 monomers. SiO2 monomers were not homogeneously deposited on nonspherical Au and CdSe/Cd(1-x)Zn(x)S nanocrystals. A surface silanization process, partly hydrolyzed tetraethyl orthosilicate were attached to the nanocrystals instead of initial ligands, plays an important role for the nanocrystals coated homogeneously with a SiO2 layer. Furthermore, CdSe/Cd(1-x)Zn(x)S nanocrystals were homogeneously coated with a thin SiO2 layer by the surface silanization process and a subsequent reverse micelle route. Colloidal Au nanocrystals were homogeneously coated with a SiO2 shell by the surface silanization process and subsequent Stöber synthesis without using a silane coupling agent or bulk polymer as the surface primer to render the Au surface vitreophilic. These results indicated partly hydrolyzed tetraethyl orthosilicate has an ability to replace the ligand on nanocrystals. After surface modification, the SiO2 particles with nanocrystals were conjugated with antibody for bioapplications.

Synthesis of a White-Light-Emitting ZnSe:Mn Nanocrystal via Thermal Decomposition Reaction of Organometallic Precursors

Low-dimensional nanosized semiconductor materials, such as quantum dots, have attracted considerable interest in the past decade. Due to their size-dependent physical and optical properties, these nanosized semiconductor materials offer various technological applications in photoelectronic devices. Among the II-VI semiconductor materials, zinc selenide (ZnSe) is of special interest due to its intense UV blue light emission at 460 nm wavelength with a band gap of 2.7 eV, which has not been observed in other well-known semiconductor materials, such as CdS and CdSe. In addition, it has been reported that when the surface of ZnSe is passivated by another semiconductor nanocrystal layer such as ZnS, a ZnSe/ZnS core shell quantum dot can be formed, and the quantum yield of the ZnSe/ZnS quantum dot is much higher (about 20 times) than that of bare ZnSe nanocrystallite. The preparation method of ZnSe or ZnSe/ZnS quantum dot often includes a thermal decomposition reaction of organometallic precursors in a hot coordinating organic solvent such as trioctylphosphineoxide (TOPO), leading to a hydrophobic surface on the resulting nanocrystal. Previously, in this lab, water-dispersible ZnSe and ZnSe/ZnS nanocrystals were also prepared by exchanging the hydrophobic nanocrystal surface with polar organic ligands such as mercaptoacetic acid (MAA) and ethylenediaminetetraacetic acid (EDTA) molecules. Manganese-ion doped ZnSe nanocrystals have been prepared in various media. In most cases, emission wavelengths of the ZnSe:Mn nanocrystals were far shifted from that of the undoped ZnSe nanocrystal. They usually emit orangecolored lights (580-600 nm) due to the dopant Mn ions. In this paper we report on the synthesis of Mn ion-doped ZnSe nanocrystal via thermal decomposition reaction from organometallic precursors, and unexpected white light emission from the prepared ZnSe:Mn nanocrystal. Figure 1 presents an HR-TEM image of ZnSe:Mn nanocrystal. In the picture, the measured and calculated average particle size was 3.5 nm. In addition, the appearance of distinct lattice planes in the fringe image with an approximate spacing of 3.4 A suggests that all the solid samples were made of single crystals rather than poly-crystalline aggregate mixtures. An energy dispersive X-ray spectroscopy diagram (EDXS, in Fig. 2) was also obtained to confirm the elemental compositions of the ZnSe:Mn nanocrystal in the solid state. The obtained doping concentration of manganese(II) ions in the ZnSe:Mn nanocrystal was 2.3 atomic %. To determine the doping concentration of Mn ions more precisely, Inductively Coupled Plasma-Atomic Emission Spectrometry (ICPAES) analysis was performed. Three trials of the sample measurements revealed that the average elemental proportion of the Mn ions relative to ZnSe parent crystal was Figure 1. HR-TEM image of ZnSe:Mn nanocrystal, the scale bar represents 5 nm.

Simulation Study of Optical Transmission Properties of ZnO Thin Film Deposited on Dif-ferent Substrates

ZnO is an important II-VI semiconductor material for devices with possible applications such as piezoelectric transducers, gas sensors, transparent electronic in solar cell, saw devices. Based on known research, ZnO is the most prom-ising in optoelectronic and optical applications, especially in UV region. An understanding of the optical properties of ZnO thin film on different substrates is also needed to obtain the optimal configuration for the best performance. In this work, we start our simulation by made a Matlab code to study the Sellmeier equation. The behavior of light transmission of ZnO/BK7 glass and ZnO/Sapphire is studied. Both the variation of thickness of ZnO film and different parameters of Sellmeier model are studied. This approach helps us to determine the best configuration (thin film / substrate) to made advices for optoelectronic applications.

Transferable pair potentials for CdS and ZnS crystals

A set of interatomic pair potentials is developed for CdS and ZnS crystals. We show that a simple energy function, which has been used to describe the properties of CdSe [E. Rabani, J. Chem. Phys. 116, 258 (2002)], can be parametrized to accurately describe the lattice and elastic constants, and phonon dispersion relations of bulk CdS and ZnS in the wurtzite and rocksalt crystal structures. The predicted coexistence pressure of the wurtzite and rocksalt structures as well as the equation of state are in good agreement with experimental observations. These new pair potentials enable the study of a wide range of processes in bulk and nanocrystalline II-VI semiconductor materials.

Theory of band gap bowing of disordered substitutional II–VI and III–V semiconductor alloys

For a wide class of technologically relevant compound III-V and II-VI semiconductor materials AC and BC mixed crystals (alloys) of the type A(x)B(1-x)C can be realized. As the electronic properties like the bulk band gap vary continuously with x, any band gap in between that of the pure AC and BC systems can be obtained by choosing the appropriate concentration x, granted that the respective ratio is miscible and thermodynamically stable. In most cases the band gap does not vary linearly with x, but a pronounced bowing behavior as a function of the concentration is observed. In this paper we show that the electronic properties of such A(x)B(1-x)C semiconductors and, in particular, the band gap bowing can well be described and understood starting from empirical tight binding models for the pure AC and BC systems. The electronic properties of the A(x)B(1-x)C system can be described by choosing the tight-binding parameters of the AC or BC system with probabilities x and 1-x, respectively. We demonstrate this by exact diagonalization of finite but large supercells and by means of calculations within the established coherent potential approximation (CPA). We apply this treatment to the II-VI system Cd(x)Zn(1-x)Se, to the III-V system In(x)Ga(1-x)As and to the III-nitride system Ga(x)Al(1-x)N.

Studies on the Preparation and Properties of Sheet Ni-Doped ZnO

ZnO is a direct wide band-gap Ⅱ-Ⅵ semiconductor material. For decades, ZnO has gained more and more attention as a wide band semiconductor. This paper introduced a modified homogeneous precipitation method to prepare sheet Ni-doped ZnO crystal. The preparation process was studied and the mechanism of this method was discussed. The properties of the sheet Ni-doped ZnO crystal and the effects of growth parameters on the quality of sheet Ni-doped ZnO crystal were studied using XTJ30-micro image manipulation system, thermal analysis system, X-ray diffraction. etc.

High sensitivity slow light interferometer based on dispersiveproperty of Ⅲ-Ⅴ and Ⅱ-Ⅵ semiconductor materials

We investigate the optical properties of Ⅲ-Ⅴ and Ⅱ-Ⅵ semiconductors. The results show that the sensitivity of the interferometer can be greatly enhanced by the dispersive property of semiconductor. Furthermore, the analyses show that the semiconductor slow light medium has a more wider working spectral range than gas slow light medium. Moreover, we experimentally demonstrate that the sensitivity of the interferometer based on the semiconductor GaAs is 3.2 times higher than those of traditional interferometers.

Lanthanide Sensitization in II−VI Semiconductor Materials: A Case Study with Terbium(III) and Europium(III) in Zinc Sulfide Nanoparticles

This work explores the sensitization of luminescent lanthanide Tb(3+) and Eu(3+) cations by the electronic structure of zinc sulfide (ZnS) semiconductor nanoparticles. Excitation spectra collected while monitoring the lanthanide emission bands reveal that the ZnS nanoparticles act as an antenna for the sensitization of Tb(3+) and Eu(3+). The mechanism of lanthanide ion luminescence sensitization is rationalized in terms of an energy and charge transfer between trap sites and is based on a semiempirical model, proposed by Dorenbos and co-workers (Dorenbos, P. J. Phys.: Condens. Matter 2003, 15, 8417-8434; J. Lumin. 2004, 108, 301-305; J. Lumin. 2005, 111, 89-104. Dorenbos, P.; van der Kolk, E. Appl. Phys. Lett. 2006, 89, 061122-1-061122-3; Opt. Mater. 2008, 30, 1052-1057. Dorenbos, P. J. Alloys Compd. 2009, 488, 568-573; references 1-6.) to describe the energy level scheme. This model implies that the mechanisms of luminescence sensitization of Tb(3+) and Eu(3+) in ZnS nanoparticles are different; namely, Tb(3+) acts as a hole trap, whereas Eu(3+) acts as an electron trap. Further testing of this model is made by extending the studies from ZnS nanoparticles to other II-VI semiconductor materials; namely, CdSe, CdS, and ZnSe.