Self-compensation of intrinsic defects in the ternary semiconductor CuGaSe2

Temperature-dependent Hall measurements have been performed on thin films of the ternary chalcopyrite CuGaSe2. Unintentionally doped samples and Na-containing samples are compared, as well as epitaxial and polycrystalline ones. Acceptor activation energies and acceptor and donor densities are extracted. Activation energies as well as defect densities vary over a wide range. We demonstrate that all samples are dominated by the same defect with an activation energy of 150 meV in the infinite-dilution limit. It is shown that the degree of compensation increases with increasing acceptor density. Thus direct evidence of self-compensation by intrinsic defects is given. CuGaSe2 containing Na shows the same defects as CuGaSe2 without Na: thus, it can be excluded that the dominant effect of Na is the introduction of a new acceptor. In addition, reduced compensation due to Na is not found; the net doping increases in spite of an increased compensation.