Optical transitions from core $d$ levels of gallium arsenide

An improved parameter-free method of joint Argand diagrams was used to expand the permittivity spectrum of gallium arsenide in a region of 19–26 eV into 12 bands of optical transitions with determining their maximum and half-width energies, as well as the oscillator strengths. The values of oscillator strengths of the obtained bands lie within an interval from 0.0009 to 0.06. In the regions of 19.2–21.3 and 24–26 eV, the permittivity spectrum was preliminarily calculated on the basis of experimental reflectance spectra with the use of the Kramers–Kronig integral relation method. The nature of the obtained transition bands is suggested in terms of the band-to-band and exciton transitions.