Carbon doping of GaAs and (In,Ga)As in solid source molecular beam epitaxy using carbon tetrabromide

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Abstract
We have grown C-doped GaAs and (In,Ga)As epitaxial layers of device quality in a standard solid source molecular beam epitaxy system using carbon tetrabromide (CBr4) as the carbon source. Dopant incorporation was relatively efficient for both GaAs and (In,Ga)As, requiring a CBr4 beam pressure of about 1×10−6 Torr to achieve a hole density of 1.5×1020/cm3. For doping in the 1019/cm3 range, hole mobilities were comparable to or slightly higher than those of Be-doped layers with the same carrier concentrations. Modulation-doped structures grown immediately after heavily C-doped GaAs layers exhibited reduced two-dimensional electron gas mobility, but the mobility recovered to previous values within 24 h. (Al,Ga)As/GaAs heterojunction bipolar transistors (emitter size=25 μm×50 μm) with C-doped bases (p=1.2×1019 cm−3) had common emitter small signal current gains averaging 86 at an emitter current density of 970 A/cm2. The relatively low gas load during growth, the lack of long-term memory effect, and the acceptable device performance indicate that CBr4 is an attractive alternative to Be for GaAs and (In,Ga)As devices grown by solid source molecular beam epitaxy.