Li Hung-Wei, Chang Chih-Wei
Center for Condensed Matter Sciences, National Taiwan University, Taipei, 10617, Taiwan.
Center of Atomic Initiative for New Materials (AI-MAT), National Taiwan University, Taipei, 10617, Taiwan.
Sci Rep. 2019 Mar 13;9(1):4362. doi: 10.1038/s41598-019-39786-y.
Based on recent works, the most desirable high-temperature thermoelectric material would be highly-doped SiGe crystals or films with sufficiently high Ge concentrations so that simultaneous enhancing the power factor and wave-engineering of phonons could be possible on the ballistic thermal conductor. However, available thin film deposition methods such as metal organic chemical vapor deposition, electron-beam evaporation, or sputtering are unable to produce highly-doped SiGe single crystals or thick films of high quality. To fabricate the desired material, we here employ liquid phase epitaxy to make highly-doped (up to 2% GaP doping) SiGe crystals with minimized concentration variations on Si (111) and (100) substrates. We find that growing SiGe (x = 0.05~0.25) crystals from Ga solvents at relatively high vacuum pressure (0.1 torr) displays significant deviations from previous calculated phase diagram. Moreover, doping GaP into SiGe is found to affect the solubility of the system but not the resulting Ge concentration. We thus plot a new pressure-dependent phase diagram. We further demonstrate that the new pressure-induced liquid phase epitaxy technique can yield SiGe crystals of much higher Ge concentrations (x > 0.8) than those grown by the conventional method.
基于近期的研究成果，最理想的高温热电材料可能是具有足够高锗浓度的高掺杂硅锗晶体或薄膜，这样在弹道热导体上就有可能同时提高功率因数和声子的波工程。然而，现有的薄膜沉积方法，如金属有机化学气相沉积、电子束蒸发或溅射，无法制备出高质量的高掺杂硅锗单晶或厚膜。为了制备所需材料，我们在此采用液相外延法，在硅（111）和（100）衬底上制备浓度变化最小的高掺杂（高达2% GaP掺杂）硅锗晶体。我们发现，在相对高的真空压力（0.1托）下从镓溶剂中生长硅锗（x = 0.05~0.25）晶体，与先前计算的相图有显著偏差。此外，发现将GaP掺杂到硅锗中会影响体系的溶解度，但不会影响最终的锗浓度。因此，我们绘制了一个新的压力依赖相图。我们进一步证明，新的压力诱导液相外延技术能够制备出锗浓度（x > 0.8）比传统方法生长的锗浓度高得多的硅锗晶体。
