Study on Surface Treatments on CdSe Wafers

The surface treatments on CdSe wafers were studied by means of SEM, XPS and micro-current test instrument. The relations between electrical properties of CdSe wafers and surface topography, composition and structure were analyzed. The results show that the change of surface composition by etching is beneficial to decrease leakage current. Meanwhile, the increase of oxygen on surface caused by passivation can largely decrease leakage current. When passivating time is 40 min, the wafers surface appears smooth and compact, which will decrease the density of surface state, the optimal electrical property of the wafer is therefore obtained.     

Influence of capping layer thickness on the polarization of photoluminescence of CdSe/ZnSe quantum dots grown by metalorganic chemical vapor phase deposition

The polarization of the photoluminescence (PL) of self-assembled CdSe quantum dots (QDs), grown by metalorganic chemical vapor phase deposition, was measured. From the (001) surface, the PL was found preferentially polarized in the direction, while from the cleaved surface in the [001] direction. The polarization of PL depends strongly on the ZnSe capping layer thickness and the PL energy. With an increase in ZnSe coverage, the intensity ratio was found to increase first, then decrease after the coverage is thicker than a critical value. Moreover, such a critical thickness is smaller for larger QDs (lower PL energies). Possible origins of the PL polarization are discussed. We suggest that besides the quantum confinement effects, the strain field in the QDs also plays an essential role in the observed polarization of PL.     

聚3-甲基噻吩修饰CdSe纳米棒复合膜电极光电化学性能研究

采用水热法制备了具有闪锌矿和纤维锌矿结构的CdSe纳米棒,纳米棒直径约100 nm,长度约300nm。当电极电势为-0.7 V时聚3-甲基噻吩(PMeT)修饰CdSe纳米棒有最大光电流。CdSe纳米棒/PMeT中存在p-n异质结,p-n异质结存在使得CdSe纳米棒/PMeT复合膜电极在长波区光电流高于CdSe纳米棒薄膜电极光电流。     

CdSe量子点的制备及荧光性能改善

主要讨论了CdSe量子点的制备及荧光性能的改善.采用水相合成方法制备了CdSe量子点,并用X射线粉末衍射仪对所合成的量子点进行表征,用荧光分光光度计研究了量子点的荧光性质.结果表明,采用样品处理温度的调节和ZnS壳层的包覆能在一定程度上改善CdSe量子点的荧光性能.     

Enhanced hydrogen production over CdSe QD/ZTP composite under visible light irradiation without using co-catalyst

A series of CdSe quantum dot (QD)/zirconium titanium phosphate (ZTP) was synthesized by solvothermal method using ethylene diamine by varying Cd to Se ratio from 1:1 to 1:4 and examined as robust catalysts for hydrogen evolution under visible light irradiation without using any co-catalyst. Extensively, the structural, optical, morphological, elemental and photoresponse spectra measurement of the composite system was studied. The catalytic activity of the materials was correlated with photoluminescence spectra, band gap energy and the photosensitization effect of CdSe quantum dot. Though neat CdSe quantum dot and zirconium titanium phosphate (ZTP) exhibited photocatalytic hydrogen evolution, the composite material showed remarkable high activity. Among these, 1CdSe quantum dot/zirconium titanium phosphate (ZTP) composite showed the highest hydrogen production (905.4 μmol) within 3 h which is consistent with low photoluminescence (PL) intensity, wide band gap energy and the photosensitization effect of CdSe quantum dot.     

Potential-triggered adsorption of CdSe nanoparticles on glassy carbon electrode for generation of electrochemiluminescence

In this work we discovered the potential-triggered adsorption of the thioglycerol stabilized CdSe nanoparticles on the glassy carbon electrode (GCE), which induced the electrochemiluminescence (ECL) of the nanoparticles coreacted with triethylamine. The increasing ECL emission was controlled by the applied potential of the electric field, with an optimized potential of +1.0 V. The adsorption event of the nanoparticles on the GCE was quantitatively identified by the stripping voltammetric analysis of Cd²⁺ ions, etc. The ECL emission was also found to be notably enhanced after the removal of the interference from the dissolved oxygen. These results would be helpful to make the full understanding of the ECL processes by the CdSe nanoparticles-tertiary amines system and promote the design of the high-sensitive bioelectronic sensors.     

CdSe band-splitting on thermal annealed films

Semiconducting polycrystalline CdSe thin films were prepared on glass substrates by chemical bath at 65 °C. As-deposited films grew in the metastable cubic sphalerite (S) crystalline structure with good stoichiometry. Upon thermal annealing (TA) in Ar+Se₂ atmosphere at different temperatures in the range 200–500 °C, the gradual phase transformation from cubic modification to hexagonal wurtzite (W) stable phase could be observed. From optical absorption measurements the fundamental energy band gap (E_g) and the second electronic transition (E_g+ΔE_g) were calculated for as-deposited and thermal annealed films. For TA350 °C, S-phase dominates the crystalline structure and only the spin orbit (ΔE_so) contribution to ΔE_g is present. Above 350 °C, the W-phase dominates and the energy splitting (ΔE_cf), owed to crystal field contribution and originated by the loss of lattice symmetry, should be added to ΔE_so in order to complete ΔE_g in the W-phase. The values ΔE_so=0.389±0.011 eV and ΔE_cf=0.048±0.018 eV were found from our analysis, and T_c=350 °C was here defined as the critical point of the phase transformation.     

Surface Oxidation as a Cause of High Open‐Circuit Voltage in CdSe ETA Solar Cells

TiO₂/CdSe/CuSCN extremely thin absorber (ETA) solar cells are found to give relatively high values of open‐circuit voltage (>0.8 V) but low currents upon annealing the cadmium selenide (CdSe) in air (500 ºC). Annealing in N₂ produces much lower photovoltages and slightly lower photocurrents. Band structure measurements show differences between the two annealing regimes that, however, appear to favor the N₂‐annealed CdSe. On the other hand, chemically resolved electrical measurements (CREM) of the cells reveal marked differences in photo‐induced charge trapping, in particular at absorber grain boundaries of the air versus N₂‐annealed systems, correlated with the formation of Cd–O species at the CdSe surface. Using transient absorption and photovoltage decay, pronounced lifetime differences are also observed, in agreement with the strong suppression of charge recombination. The results point to a multiple role of grain surface‐oxidation, which both impedes electron injection from the CdSe to the TiO_2, but, much more significantly, enhances hole injection to the CuSCN via passivation of hole traps that act as efficient recombination centers.     

半导体纳米晶体在薄膜晶体管中的应用

以非晶硅薄膜为核心的薄膜晶体管技术目前已经相当成熟,在该技术投入使用并且得以很好地优化之后,要想进一步提高薄膜晶体管的性能,就有必要开发新型的薄膜材料。近年来,由半导体纳米晶体构成的新型薄膜材料在晶体管中的应用越来越受到人们关注。利用半导体纳米晶体制备的薄膜晶体管有着较高的载流子迁移率和开关电流比,同时在其制备过程中可以在较低温度下大面积成膜,能够使用塑料等柔性衬底,因而具有明显的成本优势,发展前景广阔。着重介绍了几种颇具潜力的半导体(如硒化镉、碲化汞、硒化铅、锗、硅)纳米晶体在制备薄膜晶体管方面的应用。