| Summary: | 碩士 === 義守大學 === 電子工程學系碩士班 === 94 === Carbon doping in GaAs epilayers grown by metalorganic chemical vapor deposition (MOCVD) using CBr4 was successfully obtained . The growth rate decreased as CBr4 increased due to the etching effect of HBr caused by Br radicals. The growth rate increased while V/III ratio and TMGa flow rate increased. In addition, the growth rate increased with increasing the growth pressure and eventually saturated above 100 mbar. In the growth temperature rage of 500 to 650 °C, the growth rate decreased with increasing growth temperature.
Carbon incorporation efficiency dependence on growth parameters was also investigated. The hole concentration was increasing with increasing CBr4 flow rate and eventually saturated at high flow rate. The hole concentration was also increasing with decreasing V/Ш ratio. This is because more carbon atoms can occupy As site on the growth surface under lower AsH3 flow rate. In addition, low growth temperature and high growth pressure can increase the carbon incorporation efficiency. Finally, we found the hole mobility decreased with increasing hole concentration due to the increasing of impurity scattering.
The lattice mismatch of carbon-doped GaAs epilayers dependence on hole concentration was also described in detail. With increasing the hole concentration, the lattice mismatch of carbon-doped GaAs layers became large and all samples had the negative values. This is probably due to the covalent radius of C atoms is smaller than As atoms. While carbon atoms incorporate in the GaAs, the As sites will be occupied by carbon atoms on the growth surface and results in the decrease of the lattice constant.
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