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Abstract

The PL spectrum of In-doped CdTe is known to exhibit, in many cases, a characteristic feature (the 'W line') at about 12780 cm^-1 ( approximately=1.584 eV), for which there are contradictory assignments in the literature. Using bulk CdTe:In crystals we have found that this feature appears after heat treatment in a Te atmosphere, accompanied by a decrease in the D⁰X emission. We have measured the Zeeman effect on the W line, including its dependence on the directions of magnetic field and polarization. These data show that this line originates from the annihilation of a two-particle bound exciton localized at trigonal complexes with symmetry axes parallel to the (111) directions. By analysing level splittings and relative transition probabilities on the basis of a standard spin Hamiltonian it is found that the trigonal impurity potential is due to a 'tensional' lattice deformation and the Zeeman spectra can be described quantitatively by the parameters g_e=-1.7, K=1.08, L=-0.1 and a=0. Together with the magnitude of the diamagnetic shift, these values show that in the bound excitons the electron orbitals are rather extended and the hole orbitals are rather localized. In_i-V_Cd, In_i-A_Cd, or In_i-3A_Cd complexes (A being small-size acceptor impurities such as Li or Na) are considered to be the most probable candidates for the centres giving rise to the W line.