Excitons and band structure of highly anisotropic GaTe single crystals

Abstract

Exciton characteristics of GaTe single crystals grown by vapor-phase transport were studied by optical measurements. A hydrogenlike exciton series up to nϭ4 was clearly observed in the absorption spectra at 2 K. In the nϭ1 exciton energy region three types of exciton lines were found. By analyzing microphotoluminescence and micro-Raman-scattering spectra on the basis of group theory, it was clarified that these exciton lines are not due to different polytypes but to intrinsic exciton states. Furthermore, optical-absorption spectra in a magnetic field at 4.2 K were measured. In the Voigt configuration, one and two components for Eʈb and EЌb polarizations, respectively, were observed in the nϭ1 and 2 exciton lines. These magnetic-field dependencies cannot be interpreted on the basis of the previously proposed L-S coupling regime. The electronic band structure of GaTe was studied by the ab initio tight-binding linear muffin-tin orbitals method. It was found that GaTe is a direct-gap semiconductor and that the band edge is located at an M point of the Brillouin zone. From a comparison of exciton absorption spectra and the calculated band structure, the existence of the three types of excitons was interpreted from the viewpoint of j-j coupling. Our model calculation was also able to explain the Zeeman splitting and the diamagnetic shift of the exciton peak energies.

Angle-resolved photoemission study and first-principles calculation of the electronic structure of GaTe

“…16 Some differences can be appreciated in the unoccupied side of the DOS. By both methods, the behavior of the conduction band edge seems to be established as a mixture of s and p orbitals.…”

“…8 of Ref. 16, the path crosses out of the first BZ to neighboring ones, giving rise to the quasi-symmetrical band dispersion observed along these directions.…”

“…Also the contribution of Ga and Te d -orbitals of polarization to the conduction band edge, as well as to deeper states of the conduction band, seem to be underestimated in those calculations (mostly the Ga 4d ). As regards the band dispersion, authors seem to have used a standard six-face monoclinic BZ, 16 which does not correspond to the GaTe BZ. The band dispersion calculated along some directions in Ref.…”

“…15 Recently, these results were explained by the existence of three types of exciton 1 states due to j-j coupling, whose optical transitions are allowed under the group symmetry of this material. 16 There is still a lack of both theoretical and experimental studies on the electronic band structure of GaTe. One of the reasons for this lacuna lies on the complexity of the primitive unit cell, that contains 6 GaTe units (54 valence electrons), which has made band structure calculations hardly available up to now.…”

Lattice Vibration of Layered GaTe Single Crystals

“…The quality of GaTe crystals depends on the stoichiometry concentration deviation controlled by vapor pressures of elements Ga and Te during crystal growth, and other process parameters. This possibility has been explained by Yamamoto et al [21], based on a simple theoretical analysis.…”