超音波マイクロスペクトロスコピー技術を用いたSiC 単結晶の基礎音響特性評価

摘要

Evaluation of basic acoustic properties of 6H-SiC single crystals and determination of their acoustical physical constants were conducted using the ultrasonic microspectroscopy technology. First of all, we theoretically investigated a method of determining the acoustical physical constants of a hexagonal SiC single crystal using only bulk wave velocities. As a result, a procedure determining all the elastic and piezoelectric constants were proposed through measurements of four longitudinal wave velocities and four shear wave velocities using Y-cut, Z-cut and two rotated Y-cut specimens. Next, we prepared y-cut, Z-cut, (104)-plane, and (105)-plane specimens from 6H-SiC single crystals grown by the physical vapor transport (PVT) method. The leaky surface acoustic wave (LSAW) velocities measured at 225 MHz for each specimen were larger than those calculated using published constants by 61 to 99 m/s for all propagation directions. The velocities of longitudinal waves and shear waves measured for the range from 50 to 300 MHz were larger than those calculated by 118 to 165 m/s for longitudinal velocities and by 75 to 148 m/s for shear velocities exhibiting no velocity dispersions. Density was measured by the Archimedes principle resulting in 0.05% higher value than the published one. All independent elastic constants and piezoelectric constants were determined from the results obtained above and the published dielectric constants, resulting in the great differences from the published constants by 5% for elastic constant c_(13)~E at the maximum and by 370% for piezoelectric constant e_(33).%超音波マイクロスペクトロスコピー技術を用いて、6H-SiC 単結晶の基礎音響特性の評価と音響関連物理定数の決定を行った。まず、バルク波音速のみを用いて六方晶系のSiC 単結晶の音響関連物理定数の決定法にっいて理論的に検討した。その結果、Y-cut，Z-cut，および2枚の回転Y板を用いて、4つの縦波音速、4つの横波音速の測定から全ての弾性定数および圧電定数を決定する手順を示した。次に、物理気相輸送（PVT）法により育成した6H-SiC 単結晶からY-cut，Z-cut，（104）面，（105）面の試料を準備した。各試料に対して225MHz で漏洩弾性表面波（LSAW）速度の測定を行なった結果、文献の定数を用いた計算値に比べ、全ての伝搬方向で61～99 m/s大きかった。50～300 MHz の範囲で縦波音速および横波音速を測定した結果、速度分散は見られず、縦波音速で118～165m/s、横波音速で75～148m/s だけ計算値よりも測定値が大きかった。密度はアルキメデスの原理に基づいて測定したところ、文献値よりも0.05％大きい値を得た。これらの結果と文献値の誘電率を用いて音響関連物理定数を決定した結果、最大で弾性定数c_(13)~E で5％、圧電定数e_(33) で370％の文献値との差を示した。