The use of CBr 4 and SiBr 4 doping in MOMBE and application to InP-based heterojunction bipolar transistor structures

Abstract

The use of silicon tetrabromide and carbon tetrabromide for n- and p-type doping respectively of In 0.53Ga 0.47As and InP materials grown by metalorganic molecular beam epitaxy (MOMBE) has been investigated. Controllable n-type doping concentrations from 1 × 10 16cm −3 to 6 × 10 19cm −3 have been obtained in InP using SiBr 4 and tertiarybutylphosphine (TBP). Silicon doping concentrations from n = 1 × 10 16cm −3 to 1 × 10 19cm −3 have been obtained in InGaAs grown using tertiarybutylarsine (TBA). Slightly lower concentrations were obtained when using tris-dimethylaminoarsenic (DMAAs) as the arsenic source. A memory effect has been observed when transitioning from heavily to lightly doped layers, and is attributed to accumulated SiBr 4 evaporating from uncooled surfaces in the growth chamber. Carbon doping of InGaAs to carrier concentrations of 8 × 10 19cm −3 have been obtained with CBr 4 and TBA; however, significantly lower p-type doping levels are obtained when DMAAs is used as the arsenic source. We attribute this behavior to the DMAAs decomposition products reacting with carbon on the wafer surface. Secondary ion mass spectroscopy (SIMS) profiling of heavily Si- and C-doped materials indicates that bromine incorporation is below the detection level of our instrument (< 10 15cm −3). These dopant sources have been used for the growth of InP-based heterojunction bipolar transistor (HBT) structures. Both single- and double-heterojunction device structures have been produced with f t of 69–91 GHz and f max of 163–166 GHz, which are comparable to the same structures grown using conventional dopant sources.