Vacancy ordered structure of the III2VI3compound semiconductor (GaxIn1−x)2Se3studied by electron diffraction and microscopy

Abstract

The crystal structure of (Ga_xIn_1−x)₂Se₃ (x equals; 0.08–0.40), as a representative of III₂VI₃ compound semiconductors grown by a vapour transport technique, has been studied by electron diffraction and high-resolution electron microscopy. The crystal structure is a defect wurtzite, in which ¹/₃ of the cation sites are vacant. Such structure vacancies were ordered to form screws along the c-axis. The space group is P6₁ or P6₅ and the lattice constants are a equals; √3a _w equals; 6.92 Å, c equals; 3c_w equals; 18.87 å, Z equals; 6 at the composition x equals; 0.38, where the sufi w denotes the axes referred to the wurtzite structure. This suggests that the lattice mismatch between the c plane and the (111) plane of GaAs becomes zero. The c _w/a _w value is equal to 1.573, being much smaller than 1.633, the ideal value of the wurtzite structure. Systematic displacements of atoms from the atomic positions of the ideal wurtzite structure were simply characterized by the displacements of the 2-coordinated Se atoms around the vacancies: 30° rotation of the 2-coordinated Se atom toward the [001] direction and 9% shrinkage of the bond length between the 2-coordinated Se atom and the two neighbouring group-III atoms.