The appearance of superconductivity in GaP and GaAs samples highly doped with Cr

Bulk GaAs and GaP samples, highly doped with Cr, were grown by the liquid encapsulated Czochralski (LEC) method. Magnetic measurements revealed type I superconductivity with T(c) approximate to 6.2 K and H(c) similar to 600 Oe, identical for both compounds. The presence of amorphous inclusions of gallium, due to specific cellular structures of the defects in the crystals grown by the LEC method, may explain existing superconductivity as a result of a phase transition leading to beta-Ga during cooling down of the sample. Since the observed parameters are also close to the parameters characteristic for superconducting Ga II we are not ruling out this possibility.