Carbon tetrachloride doped Al_xGa_1-xAs grown by metalorganic chemical vapor deposition

A dilute mixture of CCl₄ in H₂ has recently been shown to be a suitable carbon doping source for obtaining p-type GaAs grown by metalorganic chemical vapor deposition (MOCVD) with carbon acceptor concentrations in excess of 1×10¹⁹ cm^-3. To understand the effect of growth parameters on carbon incorporation in CCl ₄-doped Al_xGa_1-xAs, carbon acceptor concentration was studied as a function of Al composition, growth temperature, growth rate, and CCl₄ flow rate using electrochemical capacitance-voltage profiling. The carbon incorporation as a function of Al composition, growth temperature, and CCl₄ flow rate was also measured by secondary-ion mass spectroscopy. All layers were grown by low-pressure MOCVD using TMGa and TMAl as column III precursors, and 100% AsH₃ as the column V source. Increased Al composition reduced the dependence of carbon concentration on the growth temperature. Reduced growth rate, which resulted in substantially decreased carbon acceptor concentrations in GaAs, had an insignificant effect on the carrier concentration of Al_0.4Ga _0.6As. A linear relationship between hole concentration and CCl ₄ flow rate in Al_xGa_1-xAs for 0.0≤x≤0.8 was observed. These results are interpreted to indicate that adsorption and desorption of CCl_y (y≤3) on the Al_xGa_1-xAs surface during crystal growth plays an important role in the carbon incorporation mechanism.