​Main lattice features of sapphire crystals

Main lattice features of sapphire crystals

The main lattice characteristic constants of sapphire are shown in Table 2.39.

The electronic energy structure of sapphire is a typical ionic crystal electronic type. Its valence band is mainly formed by the 2p state of oxygen and has a width of 13 eV. The bottom of the conduction band is formed by the 2s state of aluminum. According to the experimental data, the forbidden band width is 9.5 eV. The (0001) plane has been shown to have two unoccupied surface regions in the forbidden band located at 2 and 8 eV below the conduction band [14].

In addition, considering the nature of lattice constants and atomic bonds, the crystal plane electronic structure determined by the type of ions occupying the crystal surface must be considered during the epitaxial growth of sapphire. Even parallel sections can end with different ions (Fig. 2.13a). )[14].

The cross-section A plane ends with Al and O layers, while the cross-section C plane ends with two equivalent Al layers, etc. The charge densities and their distributions in the different intersections have been calculated [14]. The distribution of charge density around the ion, with the minimum and maximum values of 0.005 and 0.050e/a3, respectively, see Figure 2.13b. By studying the surface bonds of the last layer and the last few layers, the surface bonds at different intersections were estimated. The cutting energy in part. The electronic structure of sapphire is responsible for the existence of electron-hole pairs with maximum absorption in the energy range of 9.0-9.25 eV at 300 K.

The cleavage of sapphire occurs at the intersection of a pair of parallel grids composed of anions. Grids with similar charges reduce the gravitational force. The greater the distance between the grids, the more pronounced cleavage is demonstrated This is achieved. In a perfect crystal, the cutting face must pass through the middle of these grids. On the bottom face with alternating layers of O-Al-Al-O-Al-O, there is no cleavage condition, while on the bottom face with O-Al-Al-O-Al-O alternating layers On the (1011) plane of the O-O-Al-O-Al-O-O-O-Al-O alternating layers, the bonding force between the O-O layers at a distance of 1.06 Å is weakened.

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