Abstract

GaAsN layers were grown on GaAs(100) substrates by MBE employing a radio frequency (RF) plasma nitrogen source, and solid sources for Ga and As. The growth temperature was varied from 420 to 600 °C, and the GaAsN growth mode was in-situ monitored by reflection high-energy electron diffraction (RHEED). The optical properties of the layers were studied by photoreflectance spectroscopy (PR), phase modulated ellipsometry (PME), and photoluminescence. For the growth temperature of 420 °C the films grew in a three-dimensional (3D) mode as indicated by the appearance of transmission spots in the RHEED patterns. In contrast, GaAsN layers grown at higher temperatures presented a two-dimensional (2D) growth mode. These GaAsN layers are pseudomorphic according to high resolution x- ray diffraction (HRXRD). The PR spectra of all samples exhibited Franz-Keldish oscillations (FKO) above of the GaAs band-gap energy. From these oscillations we obtained the built-in internal electric field intensity (F _int ) at the GaAsN/GaAs interface. In the low energy region of the PR spectra we observed the transitions associated to the fundamental band-gap of the GaAs_1-xN_x layers. The variation of the GaAsN fundamental band -gap obtained by PR as a function of the N content was explained according the band anticrossing model (BAC). On the other hand, the E₁ and E₁+ ∆E₁ critical points were obtained from the analysis of spectra of the imaginary part of the dielectric function obtained by PME. We observed a shift of these critical points to higher energies with the increase of N content, which was explained by a combination of strain and alloying effects.

Keywords: III-V-N semiconductors; MBE; Optical properties; Structural characteristics