• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.4 no.2
• /
• pp.131-133
• /
• 1994

Deposition of silicon on pretreated sapphire substrates has been investigated by the liquid phase epitaxy method at low temperatures. An average 14 $\mu\textrm{m}$ thickness of silicon was grown over a large area on sapphire substrate originally coated with a much thinner silicon layer $[0.5 \mu\textrm{m} (100) Si/(1102) sapphire]$ at low temperatures from $(380^{\circ}C to 460^{\circ}C)$.

• Korean Journal of Metals and Materials
• /
• v.50 no.8
• /
• pp.605-611
• /
• 2012

ZnO nanostructures were grown on R-plane sapphire substrates with seed layers annealed at different temperatures ranging from 600 to $800^{\circ}C$. The properties of the ZnO nanostructures were investigated by scanning electron microscopy, high-resolution X-ray diffraction, UV-visible spectrophotometer, and photoluminescence. For the as-prepared seed layers, ZnO nanorods and ZnO nanosheets were observed. However, only ZnO nanorods were grown when the annealing temperature was above $700^{\circ}C$. The crystal qualities of the ZnO nanostructures were enhanced when the seed layers were annealed at $700^{\circ}C$. In addition, the full width at half maximum (FWHM) of near-band-edge emission (NBE) peak was decreased from 139 to 129 meV by increasing the annealing temperature to $700^{\circ}C$. However, the FWHM was slightly increased again by a further increase in the annealing temperature. Optical transmittance in the UV region was almost zero, while that in the visible region was gradually increased as the annealing temperature increased to $700^{\circ}C$. The optical band gap of the ZnO nanostructures was increased as the annealing temperature increased to $700^{\circ}C$. It is found that the optical properties as well as the structural properties of the rod-shaped ZnO nanostructures grown on R-plane sapphire substrates by hydrothermal method are improved when the seed layers are annealed at $700^{\circ}C$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 1998.06a
• /
• pp.67-70
• /
• 1998

In this work, the freestanding GaN single crystalline substrates without cracks were grown by hydride vapor phase epitaxy (HVPE). The GaN substrates, having a current maximum size of 350 $\mu\textrm{m}$-thickness and 10${\times}$10 $\textrm{mm}^2$ area, were obtained by HVPE growth GaN on sapphire substrate and subsequent mechanical removal of the sapphire substrate. A lattice constant of c$\_$0/=5.18486 ${\AA}$ and a FWHM of DCXRD was 650 arcsec for the single crystalline freestanding GaN substrate. The low temperature PL spectrum consist of excitonic emission and deep donor to acceptor pair recombination at 1.8 eV. The Raman E$_2$ (high) mode frequency was 567 cm$\^$-1/ which was the same as that of strain free bulk single crystals. The Hall mobility and carrier concentration was 283 $\textrm{cm}^2$/V$.$sec and 1.1${\times}$10$\^$18/ cm$\^$-3/, respectively. The freestanding and crack-free GaN single crystalline substrate suitable for the homoepitaxial growth of GaN, and the HVPE method are promising approaches for the preparation of large area, crack-free GaN substrates.

• Proceedings of the Korea Association of Crystal Growth Conference
• /
• 1998.06a
• /
• pp.157-159
• /
• 1998

Sapphire crystals were grown by Horizontal Bridgman method. The effects of sliding rate (growth rate) of Molybdenum container, growth atmosphere, temperature gradient and orientation of see on crystal qualities were investigated. The size of the crystals grown was up to 150-200 mm in length, 90 mm in width and 25-35 mm in thickness. Crystals grown under the optimum conditions were colorless, transparent and could not be observed and macroscopic defects, such as bubbles, cracks, twins and mosaic structure. With the grown crystals, prototypes of sapphire substrate for blue wafers were characterized. As a result, we can get hight quality of sapphire wafers with c-axis, 1.5 inches in diameters and 0.33 mm in thickess.

• KIEE International Transactions on Electrophysics and Applications
• /
• v.3C no.6
• /
• pp.241-245
• /
• 2003

ZnO thin films on (l00) p-type Si and sapphire substrates have been deposited by a pulsed laser deposition technique using an Nd:YAG laser with a wavelength of 266 nm. The influence of the deposition parameters such as oxygen pressure, substrate temperature and laser energy density on the properties of the grown films was studied. The experiments were performed for substrate temperatures in the range of 200∼50$0^{\circ}C$ and oxygen pressure in the range of 100∼700 sccm. All of the films grown in this experiment show strong c-axis orientation with (002) textured ZnO peak. With increasing substrate temperature, the FWHM (full width at half maximum) and surface roughness were decreased. In the case of using sapphire substrate, the intensity of PL spectra increased with increasing ambient oxygen flow rate. We investigated the structural and morphological properties of ZnO thin films using X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2007.06a
• /
• pp.106-107
• /
• 2007

We fabricated anodic aluminium oxides (AAO) on Si and sapphire substrates from the electrochemical reactions of thin AI films in an aqueous solution of oxalic acid. The thin AI films have deposited on Si and Sapphire substructure by using E-beam evaporation and thermal evaporation, respectively. The formation of AAO structures has investigated from FE-SEM measurement image and showed randomly distributed phase of nanoholes instead of the periodic lattice of photonic crystals. The AAO structure on sapphire shows the double layers of nanoholes.

• Journal of the Korean Vacuum Society
• /
• v.8 no.4B
• /
• pp.514-518
• /
• 1999

Gold (Au) is not supposed to react with sapphire(single crystalline ) under thermodynamic equillibrium, therefore, a strong adhesion between these two dissimilar materials is not expected. However, pull test showed that the gold film sputter-deposited onto annealed and pre-sputtered sapphire exhibited very strong adhesion even without post-deposition annealing. Strongly and weakly adhered samples as a result of the pull testing were selected to investigate the adhesion mechanisms with Auger electron spectroscopy. The Au/ interfaces were analyzed using a new technique that probes the interface on the film using Auger electron escape depth. It revealed that one or two monolayers of Au-Al-O compound formed at the Au/Sapphire interface when AES in the UHV chamber. It showed that metallic aluminum was detected on the surface of sapphire substrates after irradiating for 3 min. with 7keV Ar+ -ions. These results agree with TRIM calculations that yield preferential ion-beam etching. It is concluded that the formation of Au-Al-O compound, which is responsible for the strong metal-ceramic bonding, is due to ion-induced cleaning and reduction of the sapphire surface, and the kinetic energy of depositing gold atoms, molecules, and micro-particles as a driving force for the inter-facial reaction.

• Proceedings of the KIEE Conference
• /
• 2009.07a
• /
• pp.1279_1280
• /
• 2009

Vanadium dioxide(VO2) has been reported to be the most attractive material for thermochromic windows due to its semiconductor-metal phase transition at around $68^{\circ}C$. However, our previous experiment showed it is difficult to grow VO2 thin films directly on glass substrate, whereas thermochromic VO2 thin films were successfully grown on R-cut sapphire substrate. Properties of VO2 thin films on different orientations of sapphire substrates were already reported. Furthermore, VO2 thin films were successfully grown heteroepitaxially on (001) preferred oriented ZnO coated glass. We deposited VO2 thin films using V2O5 targets on substrates with various lattice parameters with same orientation(SrTiO3, MgO, and Sapphire substrate of (001) orientation) by pulsed laser deposition. In this work, we will discuss the effects of lattice misfit, substrate-induced stress and grain size on the properties of VO2 thin films deposited on various substrate materials.

• 한국초전도학회:학술대회논문집
• /
• v.10
• /
• pp.155-159
• /
• 2000

YBCO step-edge dc SQUID magnetometers on sapphire substrates have been fabricated. CeO2 buffer layer and YBCO films were deposited in situ on the low angle (${\sim}$35$^{\circ}$) steps formed on the sapphire substrates. Typical 5-${\mu}$m-wide junction has R$_n$ of 5 ${\omega}$ and I$_c$ of 50 ${\mu}$A with large I$_c$R$_n$ product of 250 ${\mu}$V at 77K. According to applied bias current, depth of voltage modulation was changed and maximum voltage was measured 16 ${\mu}$V. Field noise of do SQUID was measured 100${\sim}$300 fT/${\surd}^{Hz}$ in the 1 $^{kHz}$, and about 1.5 pT/${\surd}^{Hz}$ in the 1/f region. For ac bias reversal method, field noise was decreased in the 1/f region. The QRS peak of magnetocardiogram was measured 50 pT in the magnetically shielded room.

• Progress in Superconductivity
• /
• v.1 no.2
• /
• pp.146-150
• /
• 2000

Step edge Josephson junctions in c-axis oriented $YBa_2Cu_3O_7$ films were fabricated on $CeO_2$ buffered sapphire substrates. The step angle was controlled in the wide range of $20^{\circ}\sim75^{\circ}$ by the Ar ion milling technique. I-V curves of junction fabricated on the thickness ratio of $\sim$0.8 and the step angle of $35^{\circ}$ were exhibited RSJ-like behavior with $I_CR_N$ product of $\sim250{\mu}A$ and critical current density of $\sim2\times10^4A/cm^2$ at 77 K. Critical current of step edge junction was increased linearly with decreasing temperature but the normal resistance was almost constant. Total samples of step edge Josephson junction was satisfied a scaling behavior of $I_CR_N{\propto}(J_C)^{0.5}$.