2015, Vol.25, No.4

Journal of the Korean Crystal Growth and Crystal Technology 2023 KCI Impact Factor : 0.19

pISSN : 1225-1429 / eISSN : 2234-5078
https://journal.kci.go.kr/jkcgct

Aluminum nitride (AlN) single crystals have attracted much attention for a next-generation semiconductor application because of wide bandgap (6.2 eV), high thermal conductivity (285W/m · K), high electrical resistivity (≥ 10 14 Ω · cm), and high mechanical strength. The bulk AlN single crystals or thin film templates have been mainly grown by PVT (sublimation) method, flux method, solution growth method, and hydride vapor phase epitaxy (HVPE) method. Since AlN suffers difficulty in commercialization due to the defects that occur during single crystal growth, crystalline quality improvement via defects analyses is necessary. Etch pit density (EPD) analysis showed that the growth misorientations and the defects in the AlN surface exist. Transmission electron microscopy (TEM) and electron back-scattered diffraction (EBSD) analyses were employed to investigate the overall crystalline quality and various kinds of defects. TEM studies show that the morphology of the AlN is clearly influenced by stacking fault, dislocation, second phase, etc. In addition EBSD analysis also showed that the zinc blende polymorph of AlN exists as a growth defects resulting in dislocation initiator.

Bi2Te3-Bi2Se3 alloy which is typical n-type thermoelectric material were grown by traveling heater method (THM) technique. We investigate the effect of the composition of 100-x(Bi2Te3) - x(Bi2Se3) and doping of n-type dopants such as SbI3 and CdCl2. Maximum figure of merit of Bi2Te3-Bi2Se3 alloy was observed with CdCl2 0.1 wt% (Z: 2.73 × 10−3 / K) and SbI3 0.05 wt% (Z: 2.29 × 10−3 /K). Deviation along the length of Bi2Te3-Bi2Se3 ingot grown by THM method is low, which indicates that the ingot is very homogenized. Also we observed the close relationship of between anisotropy ratio and dopant in the 90(Bi2Te3) - 10(Bi2Se3) alloys. And we confirmed the fact that anisotropy ratio exerts thermoelectric performance in Bi2Te3 based n-type thermoelectric material.

Effects of the shape, the size and the material of head mass on performances of tonpilz transducer were studied with a finite element method. The shape of head mass was changed with an angle between symmetric axis and side of head mass of transducer from 0 to 60 degree. As a result of the simulations, the bandwidth leached to 86.4 % at 35.5 degree in case of Al head mass. The size of head mass showed a decrease in the power of transducer with little change of bandwidth. For the Ti head mass, the transmitted power showed 100 % increase with a bandwidth of 88.1 % even though the weight of the head mass increased to 167 % of Al. This can be attributed to the mechanical properties like elastic modulus of Ti relative to Al.