Solution CBr4: an improved MOVPE dopant source

Carbon has been widely used as a p-type dopant in AlGaAs and InGaAs alloys due to its lower diffusion rate, higher solubility and lower memory effect than beryllium, magnesium and zinc. Carbon tetrabromide (CBr₄) has become increasing favoured out of all the halocarbons identified as useful source materials for providing the high doping levels required for HBT´s. However consistent transport of this relatively involatile compound has been highlighted as problematic under normal operating conditions due to its solid nature. The optimum approach to improve dosimetry control of the other major solid MOVPE source, Trimethylindium (TMI), has been to dissolve it up in an extremely involatile solvent, resulting in solution TMI^TM. A similar methodology has been applied here in the case of CBr₄. An investigation of the transport characteristics of solution CBr₄ has been performed using an ultrasonic analyser to monitor the pick up of CBr₄ vapours, and a comparison has been made with data for solid CBr₄. Solution CBr₄ has been used to dope a number of structures and improved reproducibility and control using this precursor has been demonstrated