• Journal of the Korean Vacuum Society
• /
• v.7 no.4
• /
• pp.341-347
• /
• 1998

We analyzed photoreflectance (PR) characterization of the $Al_xGa_{1-x}As$ epilayer grown by molecular beam epitaxy (MBE) method. The band-gap energy $(E_0)$ satisfying low power Franx-Keldysh (LPFK) due to GaAs buffer layer is 1.415 eV, interface electricall field $(E_i)$ is 1.05$\times$$10^4$V/cm, carrier concentration (N) is $1.3{\times}10^{15}\textrm{cm}^{-3}$. In PR spectrum intensity analysis at 300 K the $A^*$ peak below $(E_0)$ signal is low and distorted because of residual impurity in sample growth. The trap characteristic time ${\tau}_i$ of GaAs buffer layer is about 0.086 ms, and two superposed PR signal near 1.42eV consist of the third derivative signal of chemically eteched GaAs substrate and Franz-Keldysh oscillation (FKO) signal due to GaAs buffer layer.

• Korean Journal of Materials Research
• /
• v.8 no.3
• /
• pp.229-237
• /
• 1998

We grew the hexagonal GaN films on (100) Si and (00.1) sapphire substrates in the temperature range of $300~730^{\circ}C$ by the direct reaction between thermally ionized N-source and thermally evaporated Ga-source. The GaN growth rates are increased at the initial stage of GaN formation and it was saturated to some values by the coalescence of each crystallites. The oxygen signal was observed in XPS spectra for all the GaN films grown in this work, especially low- temperature grown GaN film may due to incorporation of the residual oxygen in the growth chamber. The surface of low-temperature and shorter time grown films covered only Ga-droplets. however, with increasing the both substrate temperature and the growth time GaN is growth to crystallites. and coalescence to ring-type crystallites. With sufficient supply of N-source, they were changed to platelets. In the PL spectrum measured at 20 K, we observed the impurity related emission at 3.32eV and 3.38eV.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.02a
• /
• pp.642-642
• /
• 2013

Graphene, two dimensional single layer of carbon atoms, has tremendous attention due to its superior property such as high electron mobility, high thermal conductivity and optical transparency. Especially, chemical vapor deposition (CVD) grown graphene has been used as a promising material for high quality and large-scale graphene film. Unfortunately, although CVD-grown graphene has strong advantages, application of the CVD-grown graphene is limited due to ineffective transfer process that delivers the graphene onto a desired substrate by using polymer support layer such as PMMA(polymethyl methacrylate). The transferred CVD-grown graphene has serious drawback due to remaining polymeric residues generated during transfer process, which induces the poor physical and electrical characteristics by a p-doping effect and impurity scattering. To solve such issue incurred during polymer transfer process of CVD-grown graphene, various approaches including thermal annealing, chemical cleaning, mechanical cleaning have been tried but were not successful in getting rid of polymeric residues. On the other hand, lithographical patterning of graphene is an essential step in any form of microelectronic processing and most of conventional lithographic techniques employ photoresist for the definition of graphene patterns on substrates. But, application of photoresist is undesirable because of the presence of residual polymers that contaminate the graphene surface consistent with the effects generated during transfer process. Therefore, in order to fully utilize the excellent properties of CVD-grown graphene, new approach of transfer and patterning techniques which can avoid polymeric residue problem needs to be developed. In this work, we carried out transfer and patterning process simultaneously with no polymeric residue by using a metal etch mask. The patterned thin gold layer was deposited on CVD-grown graphene instead of photoresists in order to make much cleaner and smoother surface and then transferred onto a desired substrate with PMMA, which does not directly contact with graphene surface. We compare the surface properties and patterning morphology of graphene by scanning electron microscopy (SEM), atomic force microscopy(AFM) and Raman spectroscopy. Comparison with the effect of residual polymer and metal on performance of graphene FET will be discussed.

• Journal of the Mineralogical Society of Korea
• /
• v.21 no.4
• /
• pp.397-413
• /
• 2008

In Gaya area, the Boseong kaolin deposits exhibit locally unusual occurrences such as downward enrichment of kaoin minerals, characteristic hydrothermal alterations (illite and stilbite), and phase relations among kaolin minerals in addition to the extensive weathering of anorthositic country rocks. This indicates that the kaolin deposits seem to be genetically formed as a mixed hydrothermal and residual model. The kaolin ores can be divided into five types on the basis of differences in occurrence, mineral composition and characters. These consist of two types of high-grade ores ranging above 80% in grade and low-grade ores as low as less than 80% including feldspar residuals or the peculiar impurity phase of illite-vermiculite-stilbite. Halloysite and kaolinite are mostly coexisted in the Boseong kaolin, and these kaolin minerals exhibit diverse appearances in crystallinity and morphology. Such a diversity in mineral phase and crystallinity seems to be originated from the complexity in genesis. In addition to these diverse characters of the kaolin, its applied-mineralogical characteristics such as chemical composition, thermal properties, whiteness, viscosity, and etc. made it disadvantageous in terms of ore quality.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.11a
• /
• pp.363-363
• /
• 2008

The development of dry etching process for sapphire wafer with plasma has been key issues for the opto-electric devices. The challenges are increasing control and obtaining low plasma induced-damage because an unwanted scattering of radiation is caused by the spatial disorder of pattern and variation of surface roughness. The plasma-induced damages during plasma etching process can be classified as impurity contamination of residual etch products or bonding disruption in lattice due to charged particle bombardment. Therefor, fine pattern technology with low damaged etching process and high etch rate are urgently needed. Until now, there are a lot of reports on the etching of sapphire wafer with using $Cl_2$/Ar, $BCl_3$/Ar, HBr/Ar and so on [1]. However, the etch behavior of sapphire wafer have investigated with variation of only one parameter while other parameters are fixed. In this study, we investigated the effect of pressure and other parameters on the etch rate and the selectivity. We selected $BCl_3$ as an etch ant because $BCl_3$ plasmas are widely used in etching process of oxide materials. In plasma, the $BCl_3$ molecule can be dissociated into B radical, $B^+$ ion, Cl radical and $Cl^+$ ion. However, the $BCl_3$ molecule can be dissociated into B radical or $B^+$ ion easier than Cl radical or $Cl^+$ ion. First, we evaluated the etch behaviors of sapphire wafer in $BCl_3$/additive gases (Ar, $N_2,Cl_2$) gases. The behavior of etch rate of sapphire substrate was monitored as a function of additive gas ratio to $BCl_3$ based plasma, total flow rate, r.f. power, d.c. bias under different pressures of 5 mTorr, 10 mTorr, 20 mTorr and 30 mTorr. The etch rates of sapphire wafer, $SiO_2$ and PR were measured with using alpha step surface profiler. In order to understand the changes of radicals, volume density of Cl, B radical and BCl molecule were investigated with optical emission spectroscopy (OES). The chemical states of $Al_2O_3$ thin films were studied with energy dispersive X-ray (EDX) and depth profile anlysis of auger electron spectroscopy (AES). The enhancement of sapphire substrate can be explained by the reactive ion etching mechanism with the competition of the formation of volatile $AlCl_3$, $Al_2Cl_6$ or $BOCl_3$ and the sputter effect by energetic ions.