Theoretical And Experimental Study On The Fabrication Process Of Bulk Semiconductor Materials

In this thesis, numerical simulation of physical vapor transport method(PVT) process for silicon carbide growth has been carried out theoretically. The experiments of Sulfur(S)-doped bismuth telluride(Bi2Te3)-based thermoelectric materials prepared by mechanical alloying and plasma activated sintering(MA- PAS) have been conducted. Resistance and Seebeck coefficient are further measured.As the representative material of the thirdgeneration semiconductor materials, SiC is widely used in devices working under extreme conditions with high temperature, radiation, voltage or current density due to its wide bandgap, high saturated drift velocity, excellent breakdown electric strength and chemical stability. The PVT method is the most widely used process for the growth of SiC single crystal. There exist complex physical and chemical interactions during the single crystal growth. In the PVT reactor, the device is completely enclosed; hence, it is difficult to in situ measure the thermal and concentration distributions of the growth chamber. The numerical simulation method makes an alternative way to study the process in order to get the actual production process, and to provide insightful guides on process understanding and control. The effects of axial temperature gradient, cavity pressure, seed crystal temperature have been investigated systematically. The results show that increase of axial temperature gradient, the decrease of cavity pressure or increase of the growth temperature, results in larger growth rate of SiC single crystal.Bi2Te3 is widely used in thermoelectric power generation and cooling systems, as one of the most important thermoelectric materials under current industrial applications. Though Bi2Te3-based materials, for example Bi2Te3-xSx, have excellent thermoelectric properties around room temperature. For application at medium temperature dopants of heavy metals such as Pb are usually applied. However, the heavy atoms have a negative impact on the environment during production and application. Bi2Te3-based thermoelectric materials are found to be working at medium temperature range as a replacement of the heavy metal alloys. The work in the current thesis is focused on the synthesis and measurement of this type of material. During the experiment, Bi2Te3-based bulk materials are prepared by MA-PAS,and their properties such as resistance and Seebeck coefficient are further examined. We found that by incorporating element of S, the thermoelectric electrical properties can be improved. Among the investigated materials, Bi2Te2.5S0.5 showed the most excellent potential as a candidate of application at medium temperature range for thermo-electric conversion.