Crystal Substrates

  • Gadolinium Gallium Garnet (GGG) single crystal is material with good optical, mechanical and thermal properties which make it promising for fabrication of various optical components as well as substrate material for magneto - optical films and high - temperature superconductors. It can be used for infrared optical isolator (1.3 and 1.5 um), which is made of YIG or BIG film on the GGG substrate plus birefringence parts. GGG crystal is an important substrate for microwave isolators and can be used as a HTS material, for laser technology, telecommunications, electronic.
  • Because the dielectric constant and loss microwave band of MgO single crystal is very small, and the large size MgO substrate (diameter of 2 inches and larger) can be obtained, it has currently become an important industrial HTS thin monocrystalline substrate. MgO is an excellent single crystal substrate for thin films of Ferro magnetic, Photo-electronic, semiconductor and high Tc superconductor applications. There is also a growing amount of interest in using MgO substrates for the III to V elements, and in research studying the epitaxial effects of substrates on the crystallization of polymers. Other applications include the deposition of ferro electric thin film coatings on magnesium oxide substrates. And there are also growing applications for MgO in the field of plasma display panel (PDP) technology.
  •  SrTiO3 single crystal provides a good lattice match to most materials with Perovskite structure.  It is an excellent substrate for epitaxial growth of HTS and many oxide thin films. Its lattice constant (3.905Å) fits the common high Tc superconductive material YBCO (3.88 Å) very well. It has twin-less crystal structure and very good physical and mechanical properties for film growth. It is suitable for various high Tc films such as YBCO, Bi-system, La-system and others. SrTiO3 is an excellent and wide applied High Tc superconductive single crystalline substrate.
  • Magnesium Aluminate (MgAl2O4 or spinel) single crystals are widely used for bulk acoustic wave and microwave devices and fast IC epitaxial substrates. It is also found that MgAl2O4 is a good substrate for III-V nitrides device. Spinel (MgAl2O4) is one candidate for such GaN LDs substrate. The crystallographic structure of MgAl2O4 is a spinel type (Fd3m), and its lattice constant is 8.083 A. MgAl2O4 is a relatively low-cost substrate material, which has been successfully applied to the growth of high quality GaN films. MgAl2O4 is cleaved on the (100) plane. GaN LD cavities have been obtained by simply cleaving MgAl2O4 substrates along the (100) direction, which will also work well for ZnO. MgAl2O4 crystal is very difficult to grow, due to the difficulty in maintaining a single phase structure. 
  • Lithium Aluminate  or LiAlO2 is a potential substrate for III-V nitride thin films due to its excellent lattice mismatch to GaN (<0.2% at <100> ), chemical stability at high temperature and cost effective. The lattice parameter of Lithium Dioxogallate (LiGaO2) and Lithium Aluminium Oxide (γ) (LiAlO2) crystal can match with the Gallium Nitride film very well. The mismatch coefficients are 0.2% and 1.4% only for LiGaO2 and LiAlO2, much smaller than that of the common used substrates such as <0001> sapphire (14%), <100> MgO (3%), <0001> SiC (3.5%). The Gallium Nitride film is a very important material for blue, violet, UV and white LED. A substrate material that matches the film to be grown well is very important to get a nice GaN epitaxial film.
  •   Lithium Gallate or LiGaO2 represents a promising alternative to conventional substrates for GaN due to its lattice constants, chemical and thermal stability, and potential ease of separation. Since the lattice mismatch between hexagonal GaN and LiGaO2 is only about 0.9%, this substrate is considered to be one of the most promising candidates for hexagonal GaN growth. LiGaO2 is orthorhombic with cell a=5.402 A,b=6.372 A, and c=5.007 A belonging to the space group Pna21. This means that LiGaO2 is polar crystal with respect to the c-axis. From these cell dimensions, the average value of its lattice mismatch to hexagonal GaN is estimated to be about ~1%. LiGaO2 provides a good thermal match and has a high transparency in the visible and ultraviolet regions. Therefore,  LiGaO2 is expected to be a promising substrate material for the growth of high quality hexagonal GaN thin film.  

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