Electrical activation of carbon δ-doped (Al,Ga)As grown by metalorganic vapour-phase epitaxy

Abstract

Carbon δ-doped (Al,Ga)As was grown by metalorganic vapour-phase epitaxy using trimethylaluminium (TMAl) or trimethylgallium (TMGa) as a doping precursor. The best C δ-doped Al0.3Ga0.7As has a peak hole density of 1.6 × 1019 (1.4 × 1019 for GaAs) cm−3 with a full hole profile width at half maximum of 85Å(84Åfor GaAs). For C δ-doped Al0.3Ga0.7 As grown at 630°C, the use of TMGa as a doping precursor leads to both the sheet C atom density and the free hole density increasing with an increase in the total TMGa moles introduced during a δ-doping step. As a result, the electrical activation remains almost constant with the change of TMGa moles supplied. The sheet C atom density always increases with increasing supply of TMAl, but approaches its maximum value at an amount of TMAl of 6.4 × 10−7mol. The electrical activation reduces from > 90% to < 10% when the supply of TMAl increases from 2.1 × 10−7 to 8 × 10−7mol. Regardless of the doping precursors, the hole density weakly decreases and the C atom density significantly increases with increasing growth temperature. Low growth temperatures are required for high electrical activation. Using optimised growth conditions, C δ-doped pipi doping superlattices with different average hole densities are fabricated to obtain C bulk-doped-like layers.