Wide-dynamic-range, fast-response CBr4 doping system for molecular beam epitaxy

The authors report the design and performance of a versatile carbon doping system for solid-source molecular beam epitaxy using carbon tetrabromide (CBr4). This system is capable to achieve three orders of magnitude in doping by changing the CBr4 temperature along with varying the CBr4 leak rate into the growth chamber. The CBr4 temperature is controlled using thermoelectric coolers and thus can be adjusted easily and quickly. The CBr4 vapor pressure increases more than 1 decade when its temperature increases from −5 to 20 °C. The CBr4 leak rate is controlled using six different diameter orifices connected in parallel, and the flow to each orifice can be switched on and off independently using a pneumatic valve. The fast response time of these pneumatic valves enables us to change the doping abruptly. This system is suitable for growing sophisticated structures, which require wide doping range and fast changes in doping.