采用物理气相传输法生长了Al掺杂和非掺杂的6H-SiC晶体, 测量了从室温到400℃的拉曼光谱. 由于晶体的热膨胀作用及光声子散射过程中的衰减, 导致两种样品的拉曼谱峰均向低波数移动, 并且发生展宽. 随着温度升高, Al掺杂样品中的等离子体激元增加, 使得样品中自由载流子浓度增大, 由于纵向声子与等离子体激元和自由载流子之间存在很强的耦合交互作用, 导致Al掺杂样品的A1模强度显著降低而非掺杂样品几乎不变. 通过拉曼光谱与霍耳效应测量, 从理论和实验上分析了Al在高温下的激活行为及对自由载流子的贡献.
Al-doped and un-doped 6H-SiC crystals were grown by physical vapor transport (PVT) method. Raman spectra were measured from room temperature to 400℃. The Raman requencies were shifted to lower wavenumber and Raman peaks were broadened with increasing temperature for both samples due to thermal expansion and optical phonons decay. Free carrier concentration in Al-doped sample was increased with increasing temperature due to increasing of the plasma concentration, which correspondingly enhanced more strong coupling interactions among LO phonons, plasma, and free carriers. Therefore, the intensity of A1 (LO) mode for Al-doped sample decreased obviously and maintained unchangeable for un-doped sample. The Al activation behavior and its contribution to free carriers in high temperatures were analyzed theoretically and demonstrated experimentally.
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