2007, Vol.17, No.5

Journal of the Korean Crystal Growth and Crystal Technology 2023 KCI Impact Factor : 0.19

pISSN : 1225-1429 / eISSN : 2234-5078
https://journal.kci.go.kr/jkcgct

Single crystal CdGa2Se4 layers were grown on a thoroughly etched semi-insulating GaAs (100) substrate at 420oC with the hot wall epitaxy (HWE) system by evaporating the polycrystal source of CdGa2Se4 at 630oC. The crystalline structure of the single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). The carrier density and mobility of single crystal CdGa2Se4 thin films measured with Hall effect by van der Pauw method are 8.27 × 1017 cm.3, 345 cm2/V·s at 293 K, respectively. The photocurrent and the absorption spectra of CdGa2Se4/SI (Semi-Insulated) GaAs (100) are measured ranging from 293 K to 10 K. The temperature dependence of the energy band gap of the CdGa2Se4 obtained from the absorption spectra was well described by the Varshni’s relation, Eg(T) = 2.6400 eV . (7.721 × 10.4 eV/K)T2/(T + 399 K). Using the photocurrent spectra and the Hopfield quasicubic model, the crystal field energy (Δcr) and the spin-orbit splitting energy (Δso) for the valence band of the CdGa2Se4 have been estimated to be 106.5 meV and 418.9 meV at 10 K, respectively. The three photocurrent peaks observed at 10 K are ascribed to the A1-, B1-, and C11-exciton peaks.Iat

The device performance of ZnO-thin film transistors (ZnO-TFTs) with gate dielectrics of SiO2, SiNx and Polyvinylphenol (PVP) having a bottom gate configuration were investigated. ZnO-TFTs can induce high device performance with low intrinsic carrier concentration of ZnO only by controlling gas flow rates without additional doping or annealing processes. The field effect mobility and on/off ratio of ZnO-TFTs with SiNx were 20.2 cm 2 V.1 s.1 and 5 × 10 6 , respectively, which is higher than those previously reported. The device adoptable values of the mobility of 1.37 cm 2 V.1 s.1 and the on/ off ratio of 6 × 10 3 were evaluated from the device with organic PVP dielectric.

We synthesized a series of CaS1 xSex: Eu red-emitting phosphors for application in phosphor-converted three-band white light emiting diode (LED). The photoluminescence and structural properties of CaS1 xSex : Eu were examined.The CaS1 xSex: Eu phosphors have a strong absorption at 455 nm, which is the emission wavelength of a blue LED.CaS : Eu has a red emission peak at 651 nm due to the 4f65d1 (T2g)→ 4f7 (8S7/2) transition of the Eu2+. The emission peakof CaS1 xSex:Eu is shifted from 651 to 598 nm with increasing Se content. CaS1 xSex: Eu can be used as wavelength-tunable red-emitting phosphors pumped by a blue LED. We also fabricated a three-band white LED by doping SrGa2S4:Euand CaS0.50Se0.50: Eu phosphors onto a blue LED chip.Key words CaS1 xSex: Eu, Red-emitting phosphor, White LEDCaS1xSex:Eu .... .. ....... ...†..... ... , .. , 448-701(2007. 8. 28. .. )(2007. 9. 20. .... ). . ... -.. 3.. .. .. .... (LED). ... ... ... CaS1 xSex:Eu .... ..... .CaS1 xSex:Eu. ... .. ... ..... . CaS1 xSex:Eu .... .. .. ..... .. ... 455 nm.... ... .. . Eu2+. 4f65d1 (T2g) → 4f7 (8S7/2) .. ... CaS : Eu. 651 nm.. .. .. .... ... .. .CaS1 xSex:Eu. .. .... Se. .... ... 651 nm.. 598 nm.. ... .. . CaS1 xSex:Eu .... ..LED. .... .. ... .. ... .. .... ... . .. . SrGa2S4:Eu. CaS0.50Se0.50:Eu .... .. .