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JaehyeongLee,JunsinYi,KeajoonYang,D.Mangalaraj 한국물리학회 2002 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.40 No.5
Vacuum evaporated cadmium sulphide (CdS) thin lms were implanted with Ar+ at dierent doses. The X-ray diffraction (XRD) pattern of the as-deposited film showed a hexagonal structure with a preferred orientation along the (002) plane. Formation of Cd metallic clusters was observed in ion-implanted lms from the XRD patterns. The band gap of the Ar+-implanted lms decreased from 2.385 eV for the as-deposited lm to 2.28 eV for maximum implantation whereas the absorption coecient increased with increasing implantation dose. Raman scattering due to the Al(LO) phonon was observed at 299 cm
이재형,JunsinYi,D.Mangalaraj 한국물리학회 2002 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.41 No.1
Amorphous Sb$_{2-x}$Bi$_x$Te$_3$ ($x$=0.0, 0.5 and 1.0) thin films were formed by using vacuum evaporation. In the Hall studies, a p- to n-type conduction change was observed at higher Bi concentrations, and that change was attributed to the unpinning of the Fermi level. The ac conductivity data of the Sb$_{2-x}$Bi$_x$Te$_3$ ($x$=0.0, 0.5 and 1.0) thin films were obtained using a capacitor structure with aluminium as electrodes. The temperature dependence of the ac conductivity was explained on the basis of polaronic-type conduction by comparing the numerical ac conductivity data of bipolarons and single polarons. From the comparison, it was found that the numerical bipolaron conductivity behaved similarly to that of the experimental conductivity whereas the numerical single polaron conductivity differed, thus confirming the bipolaronic nature of conduction in Sb-Bi-Te thin film systems. Higher Bi concentrations were observed to produce more dangling-bond defect states. The ac activation energy values indicated that the conductivity was of an electronic (electrons or holes) hopping type.
Influence of Nitrogen Implantation on the Structural and Optical Properties of CdS Thin Films
이재형,DonggunLim,JunsinYi,KeajoonYang,D.Mangalaraj 한국물리학회 2002 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.40 No.5
The effects of nitrogen-ion implantation on vacuum-evaporated cadmium sulphide (CdS) thin films were investigated using X-ray diffraction (XRD), optical transmittance spectra, and Raman scattering studies. X-ray diffraction studies revealed that the as-deposited CdS films had a hexagonal structure with a preferential (002) orientation. The XRD patterns revealed formation of Cd metallic clusters in the ion-implanted films. The band gap of the N$^+$-implanted films decreased from 2.385 eV for the as-deposited film to 2.301 eV for maximum implantation whereas the optical absorption coefficient values increased with increasing implantation dose. Raman scattering due to the A$_l$(LO) phonon was observed at 299 cm$^{-1}$ in the as-deposited CdS film with a large full width at half maximum (FWHM). The Raman peak position did not change much whereas the FWHM increased with the ion dose. These are attributed to the effect of implantation induced lattice damage. A decrease in the area of the Raman peak of the CdS A$_l$(LO) mode is seen on implantation.
Structural and Electrical Properties of a Y2O3 Bu er Layer by the Two Step Process
Dong-GunLim,Jae-HyeongLee,JunsinYi 한국물리학회 2002 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.40 No.1
We investigated the structural and the electrical properties of yttrium oxide (Y$_2$O$_3$) as a buffer layer for a single transistor ferroelectric random access memory (FRAM). The Y$_2$O$_3$ films were prepared by using the rf reactive magnetron sputtering method in the presence of oxygen (O$_2$) gas. The Y$_2$O$_3$ buffer layers were deposited at a low substrate temperature below 400 $^\circ$C and were treated by rapid thermal annealing (RTA). Investigated parameters were the substrate temperature, the O$_2$ partial pressure, the post-annealing temperature, and the suppression of the interfacial SiO$_2$ layer generation. The microstructure of the Y$_2$O$_3$ films was found to depend highly on the annealing temperature and on the amount of O$_2$ gas used during the deposition process. X-ray diffraction (XRD) analysis showed the Y$_2$O$_3$ films transformed from an amorphous to a polycrystalline form when the annealing temperature was increased to 800 $^\circ$C. Also, O$_2$ partial pressures of less than 10 \% were present for the peak of monoclinic yttrium oxide. For a well-fabricated sample, we achieved a leakage current density ($J_{leak}$) on the order of 10$^{-7}$ A/cm$^2$ and a breakdown electric field ($E_{br}$) of about 2 MV/cm for the Y$_2$O$_3$ film. A capacitance versus voltage analysis yielded a dielectric constant of 8.1. We successfully achieved an interface state density of Y$_2$O$_3$/Si as low as 8.72$\times$10$^{10}$ cm$^{-2}$ eV$^{-1}$. Low interface states were obtained from the very low lattice mismatch of less than 1.75 \%.
Optimum Ge Pro le for the High Cut-O Frequency and the DC Current Gain of an SiGe HBT for MMIC
김경해,JinheeHeo,SunghoonKim,D.Mangalaraj,JunsinYi,HoongjooLee,ByungryulRyum 한국물리학회 2002 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.40 No.4
This paper reports the effects of the Ge proles shape on the cut off frequency and the DC current gain of SiGe heterojunction bipolar transistors (HBT's). Device simulations using ATLAS/BLAZE for a SiGe HBT with a trapezoidal or a triangular Ge prole are carried out to optimize the device performance. A HBT with a 15 % triangular Ge profile shows a higher cut-o frequency and DC current gain than that with a 19 % trapezoidal Ge prole. It was observed that the cut-off frequency and DC current gain as 84 GHz and 600 respectively for the case of 15 % triangular Ge prole instead of 42 GHz and 200 which was observed for 19 % trapezoidal Ge profile.