Growth of CuGaSe₂ layers on closely lattice-matched GaAs substrates by migration-enhanced epitaxy

CuGaSe₂ single-crystal films are grown on the As-stabilized (2 × 4) surface of (001) GaAs by migration-enhanced epitaxy (MEE), where Cu+Ga and Se are alternately deposited. The growth process is monitored by refraction high-energy electron diffraction (RHEED) in the [110] azimuth. Under the Cu-enriched growth condition, a deformed 4-fold pattern is observed in both Cu+Ga and Se deposition periods. The deformed 4-fold pattern is found to be related to the segregation of Cu₂Se on the CuGaSe₂ surface as confirmed by the results of X-ray diffraction (XRD) measurement. By reducing the beam equivalent pressure of Cu (Cu-BEP), clear 4-fold patterns appear in both Cu+Ga and Se deposition periods instead of deformed 4-fold patterns. Further reduction of Cu-BEP results in clear 4- and 2-fold patterns for Cu+Ga and Se deposition periods. Under these growth conditions, Cu₂Se- segregation-free CGS growth is achieved. Thus, the CuGaSe₂ single-crystal layers without Cu₂Sesegregation are successfully grown on GaAs(001) substrates by optimizing the Cu-BEP.