Carbon doping of III–V compounds grown by MOMBE

Abstract

Recent advances in heterostructure bipolar transistor (HBT) technology have created a need for p-type doping at levels ≥10 20 cm -3. We have achieved p-type doping levels as high as 5×10 20 cm -3 using C, which is introduced through the use of trimethylgallium (TMG) during metalorganic molecular beam epitaxy (MOMBE) growth of GaAs. By utilizing the atomic planar doping method, we have also been able to grow C-doped spikes with hole concentrations as high as 7×10 19 cm -3, with a full width at half maximum of ∼50 Å at 300 K. This level is among the highest reported for planar doping. By switching out the TMG, and switching in the triethylgallium (TEG) to continue to growth of C-free GaAs, we have grown sandwich-type structures with C levels of 10 20 cm -3, which fall off within 210 Å to C levels of <10 17 cm -3. High temperature annealing of such structures reveals a C diffusion coefficient of <10 -16 cm 2 s -1 at 950°C, in agreement with other reports. The electrical properties of layers annealed at high temperatures appear to be influenced by the presence of strain arising from the high C concentration. X-ray diffraction patterns of 3 μm layers doped in excess of 10 20 cm -3 show a lattice constant which corresponds roughly to that calculated by assuming a Vegard law mixture of GaAs and 0.7% GaC. Preliminary results of C-doping of InGaAs will also be discussed. Finally, the usefulness of carbon doping has been demonstrated in ohmic contact formation, Schottky barrier height enhancement in MESFETs and as the base layer in HBTs.