Carbon in semi‐insulating, liquid encapsulated Czochralski GaAs

We have investigated undoped, semi‐insulating GaAs, grown by the liquid encapsulated Czochralski technique in pyrolytic BN crucibles. The concentration of carbon, the principal shallow acceptor, depends on the water content of the B2O3 encapsulant. Dry B2O3 (100–150 ppm H2O) results in carbon concentrations as high as 8×1015 cm−3, while wet B2O3 (500 ppm H2O) results in carbon concentrations below the detection limit of 3–5×1014 cm−3. In samples with carbon below 5×1014 cm−3, the compensation (acceptors minus donors shallower than EL2) is also low, and the room‐temperature carrier concentration can exceed 1011 cm−3. For samples with carbon above 5×1014 cm−3, the room‐temperature carrier concentration is below 5×107 cm−3 for all samples measured. The compensation is less than the carbon concentration in high carbon samples, indicating that donors shallower than EL2 are significant in determining the value of the compensation in these samples.