Kyung Ah Jeon

Effect of rapid thermal annealing on electrical and optical properties of Ga doped ZnO thin films prepared at room temperature

Ga doped ZnO (GZO) thin films were prepared by pulsed laser deposition on glass substrate at room temperature. Structural, optical, and electrical properties of these films were analyzed in order to investigate their dependence on oxygen pressure and rapid thermal annealing (RTA) temperature. High quality GZO films with a low resistivity of 2.92×10−4Ωcm and a transparency above 94% were able to be formed at an oxygen pressure of 3×10−2Torr and a RTA temperature of 400°C. A four point probe method, x-ray diffraction, atomic force microscopy, and ultraviolet–near-infrared grating spectrometer are used to investigate the properties of GZO films.

Laser wavelength effect on the light emission properties of nanocrystalline Si on Si substrate fabricated by pulsed laser deposition

Abstract Nanocrystalline Si (nc-Si) on p-type Si substrate has been fabricated by pulsed laser deposition (PLD) technique using a Nd:YAG laser with different wavelengths of 355, 532, and 1064 nm. Basal pressure was maintained at 1×10 −5 Torr. Si nanocrystalline thin films are fabricated in 1–3 Torr He ambient. After deposition, nc-Si has been annealed in N 2 gas. Strong violet-indigo luminescence from Si nanocrystallites has been observed at room temperature by photoluminescence (PL). Its peak energies shift to green when the wavelength of pulsed laser is increased from 355 to 1064 nm. As increasing environmental gas pressure, weak green and red emissions from annealed nc-Si was also observed by PL.

Evidence for carrier-induced ferromagnetic ordering in Zn1−xMnxO thin films: Anomalous Hall effect

The intrinsic origin of the ferromagnetic ordering in Zn1−xMnxO thin films grown by pulsed-laser deposition was investigated. The ferromagnetic behaviors for a Zn1−xMnxO (x=0.26) film grown at 700 °C under oxygen pressures of 10−1 Torr were observed at 4 and 300 K. The anomalous Hall effect (AHE) was found at temperatures of up to 210 K for the Zn0.74Mn0.26O thin film. The anomalous Hall coefficients (RA) were determined to be approximately proportional to the square of resistivity in the low field region, indicating the side-jump process for the AHE. Our results provide direct experimental evidence that a carrier-mediated mechanism is responsible for the ferromagnetic ordering in Zn1−xMnxO thin films grown by pulsed-laser deposition.

Formation mechanism and optical properties of nanocrystalline silicon in silicon oxide

Silicon nanocrystals with diameters ranging from 1.5 to 3 nm were formed on silicon substrates by using a pulsed laser deposition (PLD) followed by annealing and oxidation. The optical and structural properties of the films have been investigated as a function of deposition temperature, annealing, and oxidation process. When the deposition temperature increased, photoluminescence intensity abruptly decreased and peaks showed redshift. Annealing process can reduce the number of defect centers. Oxidation has considerable effect upon the formation and isolation of the nanocrystals. These results suggest that the formation mechanism of Si nanocrystals by using PLD could be explained by three steps of growth, passivating defect centers, and isolation, sequentially.

Biosensor with Oxide Nanowires

ZnO nanowires (NWs) were fabricated on p-Si (100) substrates by simple physical vapor deposition in vacuum furnace. Scanning electron microscopy (SEM) images indicate that the diameters of ZnO NWs were from 20 to 50 nm and the average length was longer than 2 mum. Room-temperature photoluminescence spectra of the NWs show the near band-edge emissions and the deep-level green light emissions. Such result indicates that the nanowires have good structural quality. We have fabricated electrical biosensors based on ZnO NW field effect transistors and report the chemical sensitivity of ZnO NWs. The ZnO nanosensor functionalized with biotin can easily detect streptavidin binding. The ZnO NWs for sensitive, label-free, real time detection of a wide range of biological species could be exploited in vivo diagnostics.

Blue photoluminescence of Si nanocrystallites embedded in silicon oxide

Luminescent characteristics of Si nanocrystallites have been reported depending on deposition condition. Si nanocrystalline thin films on p-type (100) silicon substrate have been prepared by pulsed laser deposition technique using a Nd:YAG laser. Strong blue photoluminescence has been observed at room temperature. The optical properties of thin films have been investigated as functions of laser energy densities, annealing gases, and target-substrate distances. These results indicate that the blue photoluminescence of Si nanocrystallites is related to the quantum size effect of Si nanocrystallites.

Synthesis of ZnO Nanowires by Pulsed Laser Deposition in Furnace

ZnO nanowires (NWs) were fabricated on Au coated sapphire (0001) substrates by using a pulsed laser deposition (PLD) system in vacuum furnace with a Q-switched Nd:YAG laser. ZnO NWs have various size and shape with a substrate position inside a furnace, and their morphologic construction is reproducible. Scanning electron microscopy (SEM) images indicate that the diameters of ZnO NWs ranged from 100 to 150 nm and the average length was greater than 3 μm. Room-temperature photoluminescence spectra of the NWs show the near band-edge emissions and the deep-level green light emissions. The formation mechanism of the NWs is discussed.