ocalized doping enhancement by photon-assisted chemical beam epitaxy

摘要

Doping results from Ar~+-laser-assisted chemical beam epitaxy with triethylgallium, tris(dimethylamino) arsenic and silicon tetrabromide as group-III, group-V and dopant precursors respectively are reported. Enhancements in the n-type doping concentration are observed with laser irradiation in the investigated substrate-temperature range 390 deg C - 500 deg C. With a 300 W/cm~2 irradiation power density, an increase in the carrier oncentration by 70 times is obtained at 390 deg C substrate temperature. A numerical model developed by us for epitaxial growth and doping with the aove precursors is used to assess the contribution of laser-induced thermal heating to the observed doping increase. A reaction scheme for photo-induced decomposition of physisorbed silicon tetrabromide is proposed. A kinetic rate equation for the photolysis is derived and used to estimate the absorption cross section required to reproduce the observed concentration enhancements resulted from laser irradiation. The possibility is established that dramatic increases in carrier concentration at low growth temperatures are due to photolysis of physisorbed silicon tetrabromide.