ZnSe epitaxial growth on zinc- and selenium-treated GaAs(001) surfaces observed by STM

The structures of both selenium and zinc treated GaAs(001) surfaces and the early stages of ZnSe growth on those surfaces have been studied using reflection high energy electron diffraction (RHEED) and in-situ scanning tunneling microscopy (STM). Upon exposure of Se, both Ga- and As-stabilized GaAs surfaces form (2 × 1) structures which were observed by RHEED at a temperature range of 250–500°C. The STM image revealed that the Se-terminated surface is well ordered and has dimer rows along the [110] direction in higher treatment temperatures. During the ZnSe growth on the Se-terminated surface, the RHEED pattern immediately became spotty (only 1–2 ML of growth). STM images of this surface showed a disordered rough surface. Thus, it was confirmed that epitaxy of ZnSe film on Se-terminated GaAs proceeded by predominantly three dimensional island growth. In the case of Zn exposure on As-stabilized (2 × 4) surfaces, there were no obvious changes in the STM image and RHEED patterns. Only a slight change was observed in the 2 × reconstruction pattern. The streaks were weaker and the spots at the Laue zone became brighter. This implies that Zn did not react with the GaAs surface but merely stuck to it. At ∼ 0.5 ML of ZnSe growth on the Zn-treated surface, streaks along the 4 × direction became weaker and the STM showed a very uniform distribution of ZnSe. The (2 × 4) stripes were still observed. This is in good agreement with a two dimensional growth mode.