|1.Research Institution||Tohoku University|
|161st Committee on Science and Technology of Crystal Growth|
|3.Term of Project||FY 1997 〜 FY 2001|
|5.Title of Project||Growth and Characterization of Single Crystals for Active Elements|
|Name||Institution,Department||Title of Position|
|Tsuguo Fukuda||Tohoku University, Institute for Materials Research||Professor|
|Names||Institution,Department||Title of Position|
|Takatomo Sasaki||Osaka University, Graduate School of Engineering||Professor|
|Kiyoshi Shimamura||Tohoku University, Institute for Materials Research||Research Associate|
8.Summary of Research Results
1. Crystal growth for ultraviolet coherent light source
a) 3-4 inch Ce:LiCaAlF6(LiCAF) and Ce:LiLuF4(LLF) single crystals could be grown in this year and could get 98mJ laser output at 290nm.
b) 2 inch GdxY1-xCa4O(BO3)3, which is the promising crystals for UV light source using their highest nonlinear constant, could be grown using solution mixing method.Consequently, the laser thresholdimproved up to 25.4GW/cm2, which is twice higher than that of previous one.
c) Oriented LaF3 thin films were successfully grown by laser abrasion method.
2. Piezoelectric crystals for digital mobile communication
a) Sr3NbGa3Si2O14(SNGS), Ca3NbGa3Si2O14(CNGS) crystals, which have smaller dependence of piezo-electric constant(d12)v.s. temperature were successfully grown by μ-PD and Cz method. They can be candidate materials for SAW filter device of digital mobile communication.
b) Stability at high temperature of SNGS and CNGS were improved by substituting Ga site with Al, so that they can also be used as torque sensor at high temperature
3. Shaped crystal growth technology and segregation control using micro-pulling-down (μ-PD) method
Modified μ-PD method was developed by precise design of the crucible shape. With modified μ-PD method, diameter and shape of crystals could be controlled.
4. Machining and crystallinity characterization of developed new functional crystals and their device application
a) We found out XPS signal of O(1s) from mixed perovskitestemmed from O ion polarization.
b) Light Scattering Tomography (LST) method allows to investigate dislocation density easily with high accuracy.
5. Design and development of new functional synthetic crystal for crystal growth engineering
a) Tb3Al5O12(TAG) has highverdet constant and promising material for faraday rotator, but because of it’s incongruency,bulk crystal growthwas regarded to be impossible. Butusing our design concept, 1-inch size TAG crystals were successfully grownby substituting Al site by Sc.
b) Tm,Ho:LiLuF4, Tm,Ho:LiYF4, Tm,Ho:Lu3Al5O12 single crystals for eye-safe laser could be grown and succeeded to obtain 2mm cw at room temperature.
c) (Nd, Sr)(Al, Nb)O3(NSAN), (La, Sr)(Ga, Nb)O3(LSGN) single crystals for GaN epitaxial wafer were developed. NSAN and LSGN have much smaller lattice mismatch with GaN of 1.04%(NSAN) and 0.62％(LSGN). We succeeded to grow GaN thick film using these crystals.
d) Ca8La1-xYbx(PO4)6O2, which has higher crystal field than other oxide were successfully grown and emission cross-section about s=2.8× 10-20cm2 was obtained. This is the best result among the oxide laser crystals.
e) Ti:b-Ga2O3 single crystal for solar cell and liquid crystal display application was developed and carrier concentration and mobility of this crystal was characterized quantitatively.
f) 1-inch size ZnO single crystals, which are candidate material for blue light emitter and GaN epitaxial wafer, were grown by the hydrothermal method.
g) Succeeded to grow SiGe bulk crystal with uniform composition and multicrystalline SiGe with large compositional distribution for new solar cell applications by directly controlling the growth temperature at the crystal-melt interface using in-situ monitoring system.
6. Control of thermal convection, spiral growth problem andheat transportation
a) Relation between rotation rate and behavior of melt was investigated when during the growth of LiCAF crystal with Cz Method.
b) Band calculation of ABF3-type fluoride perovskite materials was carried out and it revealed imaginary materials LiBeF3, NaBeF3, KBeF3, RbMgF3 and SrLiF3 must have wide band gap.
(1)Single Crystal、(2)Czochralski Method、(3)m-PD Method
(4)Fluoride Crystal、(5)Fiber Crystal、(6)Functional Material
(7)Oxide Crystal、(8)Semiconductor、(9)Crystal technology