Growth control of GaAs using short-pulse supersonic beam epitaxy

Abstract

We report the growth behavior and doping properties of GaAs short-pulse supersonic beam epitaxy (SSBE). Various GaAs films have been grown by injecting short-pulse supersonic beams of different pulsewidths generated from a pure gas of trimethylgallium (TMG) and a mixed gas of 1% TMG + 99% H 2 maintained respectively at a source pressure of 40 and 400 Torr. A growth rate of 1 10 monolayer per pulse to just one monolayer per pulse (pulse controlled layer-by-layer growth) was readily achieved by adjusting the pulsewidth of the supersonic beam. It is emphasized that the pulse controlled layer-by-layer growth achieved by the SSBE method provides a growth rate of 1 μm/h which is much higher than that obtained by conventional ALE (atomic layer epitaxy). The incorporated carbon concentration and the corresponding hole concentration in the grown films decrease when pure TMG was used from 1.6 × 10 20 to 3.3 × 10 18cm −3 with decreasing TMG pulsewidth from 100 to 5 ms. This indicates that the impurity concentration, and therefore the electrical properties of films grown by SSBE can be easily controlled by simply adjusting the pulsewidth of the supersonic beam of the source materials. Moreover, a dramatically reduced carbon concentration down to 6.5 × 10 17cm −3 (which is two orders of magnitude lower than that obtained by conventional CBE using TMG) and a significantly improved hole mobility were achieved when the TMG molecules were accelerated to a high kinetic energy of 3.9 eV by producing supersonic beams from a mixed gas of 1% TMG + 99% H 2. These results indicate that short-pulse supersonic beam epitaxy is a very promising technique to achieve highly controlled growth properties.