CARBON-TETRACHLORIDE DOPED ALXGA1-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 AlxGa1-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 Al0.4Ga 0.6As. A linear relationship between hole concentration and CCl 4 flow rate in AlxGa1-xAs for 0.0≤x≤0.8 was observed. These results are interpreted to indicate that adsorption and desorption of CCly (y≤3) on the AlxGa1-xAs surface during crystal growth plays an important role in the carbon incorporation mechanism.