G. S. Horner

Ordered vacancy compound CuIn3Se5 on GaAs (100): Epitaxial growth and characterization

Epitaxial growth of the ordered vacancy compound CuIn3Se5 has been achieved on GaAs (100) by molecular beam epitaxy from Cu2Se and In2Se3 sources. Electron probe microanalysis and x‐ray diffraction have confirmed the composition for the 1‐3‐5 phase and that the films are single‐crystal CuIn3Se5 (100). Transmission electron microscopy characterization of the material also showed it to be single crystalline. Structural defects in the layer consisted mainly of stacking faults. Photoluminescence measurements performed at 7.5 K indicate that the band gap is 1.28 eV. Raman spectra reveal a strong polarized peak at 152 cm−1, which is believed to arise from the totally symmetric vibration of the Se atoms in the lattice.

Effect of faceting on the band gap of ordered GaInP

It has been shown that under certain growth conditions the pseudobinary semiconductor alloy GaInP shows cation site ordering into the Cu‐Pt structure, and that this ordering results in a lowering of the band gap Eg from that of the disordered alloy. The Eg lowering is known to depend on growth conditions, including the orientation of the substrate. We study the dependence of Eg on epilayer thickness for GaInP grown by metal‐organic vapor‐phase epitaxy. For epilayers grown on singular (100) substrates under growth conditions conventionally used to produce ordered material, Eg decreases dramatically with increasing epilayer thickness: Eg for a 10‐μm‐thick epilayer is ∼40 meV lower than for a 1‐μm‐thick epilayer. This dependence of Eg on thickness can be understood in terms of the recently observed faceting of the GaInP growth surface.

The microstructure of spontaneously ordered GaInP2 alloy

Polarized photoluminescence, photoluminescence excitation, piezomodulated reflectivity, and resonance Raman techniques have been employed to probe the electronic structure of GaInP2 alloys exhibiting Cu–Pt ordering. The ordering induced band gap reduction and the crystal field splitting of the valence bands have been studied for samples exhibiting various degrees of ordering. Our studies provide evidence for a distribution of order parameters in spontaneously ordered GaInP2, in contrast to earlier works, which assume that uniformly ordered domains are embedded in a perfectly disordered matrix. Furthermore, the band gap reduction and the crystal field splitting obtained from our experiments are in good agreement with a theoretical model relating these quantities to the long range order parameter in the sample.