2015, Vol.25, 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

A stoichiometric mixture of evaporating materials for BaIn2S4 single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, BaIn2S4 mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The source and substrate temperatures were 620oC and 420oC, respectively. The crystalline structure of the single crystal thin films was investigated by double crystal X-ray diffraction (DCXD). The carrier density and mobility of BaIn2S4 single crystal thin films measured from Hall effect by van der Pauw method are 6.13 × 1017 cm−3 and 222 cm2/v · s at 293 K, respectively. The temperature dependence of the energy band gap of the BaIn2S4 obtained from the absorption spectra was well described by the Varshni's relation, Eg(T) = 3.0581 eV − (3.9511 × 10−3 eV/K)T2/(T + 536 K). The crystal field and the spin-orbit splitting energies for the valence band of the BaIn2S4 have been estimated to be 182.7 meV and 42.6 meV, respectively, by means of the photocurrent spectra and the Hopfield quasicubic model. These results indicate that the splitting of the Δso definitely exists in the Γ 5 states of the valence band of the BaIn2S4/GaAs epilayer. The three photocurrent peaks observed at 10 K are ascribed to the A1-, B1-exciton for n = 1 and C24-exciton peaks for n = 24.

The growth and characterization of micro sized AlGaN array structures selectively grown by metal organic chemical vapor deposition (MOCVD) on GaN stripes are reported. The shape of the AlGaN array structures depends on the size of exposed area for selective growth. The AlGaN array structures grown selectively on relatively large exposed area have regular shapes resembling those of the GaN stripes on the substrate, while samples selectively grown on relatively small exposed area have irregular shapes. The phonon frequency of the AlGaN array structures increases with increasing Al composition in the AlGaN structure. However, at relatively high Al composition (x = 0.28 in this research), the phonon frequency decreases slightly from the expected value not only because of large tensile strain associated with large differences between the lattice constants of the AlGaN structure and underlying GaN stripes but also changes of crystal facet direction during the selective growth.

Gemological and spectroscopic properties of HPHT synthetic diamonds from New Diamond Technology (NDT) company in St. Petersburg (Russia) were examined. Their color (colorless, near-colorless with some boron and Fancy blue with high boron content) and clarity (VVS-SI1) grades were comparable to those of top natural diamonds. NDT synthetic diamonds fluoresced and phosphoresced blue or orange under SWUV light. Photoluminescence spectra revealed H3 center with very small intensity and NV centers. The intensity of H3 in NDT synthetic diamond has very weak in comparison with natural one. Using a combination of gemological and spectroscopic tests, gem-quality synthetic diamonds from NDT can be distinguished from natural diamonds of similar quality.