Diamagnetic shift of the A free exciton in CuGaSe2 single crystals

Abstract

Single crystals of CuGaSe 2 were studied using magnetophotoluminescence in magnetic fields up to 20 T at 4.2 K. The rate of the diamagnetic shift in the A free exciton peak was determined to be 9.82ϫ 10 −6 eV/ T 2 . This rate was used to calculate the reduced mass as 0.115m 0 , the binding energy as 12.9 meV, the Bohr radius as 5.1 nm and an effective hole mass of 0.64m 0 ͑m 0 is the free electron mass͒ of the free A exciton using a low-field perturbation approach and the hydrogenic model.

A Magneto‐Reflectivity Study of CuGaSe2 Single Crystals

“…The determined A hole mass has the same value as the one determined earlier using weak field MPL measurements . Our experimental hole masses are significantly greater than the density of state hole masses of 0.32 m 0 and 0.29 m 0 theoretically determined for the A and B holes, respectively .…”

“…The charge carrier effective masses affect the transport properties of semiconductor devices determining the mobility which is of a direct importance for solar cell technology development. Such masses can be measured experimentally from magneto‐optical spectra of free excitons, comprising electrons from the conduction band, and holes from the valence band, under the influence of magnetic fields . Increasing magnetic fields blue shift the energy level of these excitons.…”

“…Magneto‐optical measurements have been used to determine exciton reduced masses and Bohr radii separately for the A, B, and C excitons in CuInSe 2 as well as the A and BC excitons in CuInS 2 providing an opportunity to determine hole masses corresponding to these sub‐bands. For CuGaSe 2 only the A exciton shifts in magnetic fields have been examined by magneto‐photoluminescence (MPL) whereas shifts of both the A and B excitons can be examined simultaneously analyzing magneto‐reflectivity spectra which provides a chance to determine the A and B‐hole masses. The B‐hole mass in CuGaSe 2 has been determined only theoretically .…”

“…The orientation of the lattice structure of the measured crystals with respect to the magnetic field direction was not examined. More details about the experimental set up can be found elsewhere …”

Anisotropy of effective masses in CuInSe2

“…Recently 28 In conclusion, the diamagnetic shifts of the A and B free exciton lines in the photoluminescence spectra of CuInSe 2 single crystals reveal a considerable difference for magnetic fields applied perpendicular and parallel to the tetragonal direction z of the chalcopyrite lattice, providing an experimental demonstration of valence band anisotropy in CuInSe 2 . The exciton reduced masses are calculated within the low field approximation assuming theoretical anisotropic dielectric constants and using a first order perturbation model for non-degenerate independent excitons.…”