Photoreflectance study of the fundamental optical properties of (Ga,Mn)As epitaxial films

Abstract

Fundamental optical properties of thin films of (Ga,Mn)As diluted ferromagnetic semiconductor with a low (1%) and high (6%) Mn content and of a reference GaAs film, grown by low-temperature molecular-beam epitaxy, have been investigated by photoreflectance (PR) spectroscopy. In addition, the films were subjected to complementary characterization by means of superconducting quantum interference device (SQUID) magnetometry, Raman spectroscopy, and high resolution X-ray diffractometry. Thorough full-line-shape analysis of the PR spectra, which enabled determination of the E 0 electronic transition in (Ga,Mn)As, revealed significant differences between the energy band structures in vicinity of the Γ point of the Brillouin zone for the two (Ga,Mn)As films. In view of the obtained experimental results the evolution of the valence band structure in (Ga,Mn)As with increasing Mn content is discussed, pointing to a merging the Mn-related impurity band with the host GaAs valence band for high Mn content.

GaMnAs: Position of Mn-d levels and majority spin band gap predicted from GGA-1/2 calculations

“…4, we plot these results and compare them with other theoretical calculations and also with some experimental measurements available for small Mn composition. The values of Dietl et al 34 and Tsuruoka et al, 35 37 respectively, a very good agreement is seen between the theoretical and experimental results. Our GGA-1/2 findings are also endorsed by the theoretical calculations of Turek et al, 33 performed in a tight-binding framework.…”

Electronic- and band-structure evolution in low-doped (Ga,Mn)As

“…These results are in agreement with the results of our earlier PR spectroscopy measurements for (Ga,Mn)As layers with Mn content of 1% and 2%. 15 On the other hand, in (Ga,Mn)As layers with much higher Mn content, of 4% and 6%, we revealed significant decrease in the bandgap-transition energy. 15 We interpreted those results in terms of a disordered valence band, formed as a result of merging the Mn Ga -related impurity band with the host GaAs valence band, which extended within the band gap with increasing Mn content in (Ga,Mn)As layer.…”

“…30 In our previous investigations, with (Ga,Mn)As layers of higher (up to 6%) Mn content and thicknesses up to 300 nm, we observed the below-band-gap feature in the PR spectra of all the layers. 15 The full-line-shape analysis of experimental PR spectra shown in Fig. 3, performed by using complex Airy functions and their derivatives, 31 …”

“…15 Calculations were done using the Levenberg-Marquardt algorithm with the Matlab 8.1 computer code. The functional form of the Seraphin coefficient α was applied.…”

“…15 From analysis of the PR spectra we obtained the interband transition energies in (Ga,Mn)As layers with various Mn contents. In (Ga,Mn)As with a low (up to 2%) Mn content this energy was slightly increased with respect to that in the reference GaAs layer, which was interpreted as a result of the Moss-Burstein shift of the absorption edge due to the Fermi level location below the top of the GaAs valence band, 16 in agreement with the Zener model.…”