Effects of ordering on the optical properties of GaInP2

GaInP2 lattice-matched to GaAs or Ge plays an important role in state-of-the-art III-V multijunction solar cells. The fundamental band gap of constant-composition GaInP2 can be varied by as much as 100meV in metal-organic chemical vapor deposition (MOCVD) grown material by adjusting growth parameters that affect the degree of Cu-Pt ordering. These changes in the band gap of GaInP2 due to ordering can be exploited in the design of III-V solar cell devices. In order to accurately model the performance of these devices, accurate values of the optical constants of all layers are required. Previous literature reports of the optical properties of GaInP2 have primarily focused on highly disordered material or higher energy transitions in ordered material. While it has been noted that ordered GaInP2 material results in anisotropic optical properties, the bulk optical properties of GaInP2 as a function of ordering have not been sufficiently recorded in the literature for good optical modeling of III-V solar cell devices. In this paper, we present the dielectric functions for a range of ordered/disordered GaInP2 measured over the range 0.7-5.0 eV using spectroscopic ellipsometry. Data analysis of generalized ellipsometry data utilizing anisotropic multilayer models allows us to report accurate dielectric functions for both the ordinary and extraordinary optical axes.