Crystal growth of large sapphire and its optical properties

Abstract

Large sapphire crystals for 200-mm LED wafers were successfully grown by the top seeded melt growth (TSMG) method. The sapphire had excellent crystallinity as LED substrates. However, in the as-grown crystal, there was remarkable absorption in UV region caused by the F-center (V Â O ). To reduce the absorption, we studied several heat treatment methods using oxidized atmospheres. In air or O 2 atmospheres, the absorption was difficult to reduce because oxygen diffusion was slow and new absorption occurred. We found that heat treatment in an H 2 O 2 combustion flame was highly effective in reducing the absorption in the UV region. After the combustion flame heat treatment, the sample had an absorption coefficient less than 0.5 cm 1 at 200 nm, and no photoluminescent emissions were caused by color centers. Consequently, sapphire crystals grown by the TSMG method had good crystallinity and low absorption in the UV region.

Optical transmittance investigation of 1-keV ion-irradiated sapphire crystals as potential VUV to NIR window materials of fusion reactors

“…After annealing, F-type centers are expected to decrease through lattice reordering or oxygen (O) atom recapture. [24][25][26] Figure 3 shows the optical absorption coefficients of the H-ion irradiated sapphire crystal at 210 nm after isochronal annealing. A non-irradiated sample is also similarly investigated for comparison.…”

Magnetic sensitivity of the Microwave Cryogenic Sapphire Oscillator

“…In a second step we added to the model 150 ppb of Cr 3+ ions, and obtained the dashed line shown in the figure 9, which represents well the experimental observations. This procedure has been also applied to a second sapphire crystal coming from another manufacturer and elaborated using the Top Seeded Melt Growth (TSMG) process 28 . This second crystal is designed as SHI-18-01 and presents for the W GH 15,0,0 mode a turnover temperature of 7 K. The table I reports the paramagnetic ion concentrations determined with the above described method.…”