Development of molecular beam epitaxy (MBE) of two-dimensional (2D) layered materials is an inevitable step in realizing novel devices based on 2D materials and heterostructures. However, due to existence of numerous polytypes and occurrence of additional phases, the synthesis of 2D films remains a difficult task. This paper reports on MBE growth of GaSe, InSe, and GaTe layers and related heterostructures on GaAs(001) substrates by using a Se valve cracking cell and group III metal effusion cells. The sophisticated self-consistent analysis of X-ray diffraction, transmission electron microscopy, and Raman spectroscopy data was used to establish the correlation between growth conditions, formed polytypes and additional phases, surface morphology and crystalline structure of the III–VI 2D layers. The photoluminescence and Raman spectra of the grown films are discussed in detail to confirm or correct the structural findings. The requirement of a high growth temperature for the fabrication of optically active 2D layers was confirmed for all materials. However, this also facilitated the strong diffusion of group III metals in III–VI and III–VI/II–VI heterostructures. In particular, the strong In diffusion into the underlying ZnSe layers was observed in ZnSe/InSe/ZnSe quantum well structures, and the Ga diffusion into the top InSe layer grown at ~450 °C was confirmed by the Raman data in the InSe/GaSe heterostructures. The results on fabrication of the GaSe/GaTe quantum well structures are presented as well, although the choice of optimum growth temperatures to make them optically active is still a challenge.
The paper reports on molecular beam epitaxy of ZnSe/InSe/ZnSe quantum well (QW) heterostructures grown on GaAs(001) substrates as well as studies of their structural properties. The structures were characterized by reflection high energy electron diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy techniques. The evolution of surface morphology of QW heterostructures as a function of the InSe thickness has been studied. The quasi van der Waals growth of ZnSe on the InSe(0001) surface has been demonstrated, with the ZnSe(111) plane being oriented parallel to the (0001) plane of InSe because of a small lattice mismatch between InSe and ZnSe(111).
This paper reports on molecular beam epitaxy of GaSe 2D-layers on GaAs(001) substrates at growth temperatures of TS ≈ 400-540 • C as well as studies of their structural and optical properties. Transmission electron microscopy and the Raman spectroscopy techniques have established a correlation between the molecular beam epitaxy growth conditions and the GaSe polytypes being formed. It has been shown that GaSe layers grown at TS ≈ 400 • C can be characterized as a γ-GaSe polytype with a rhombohedral crystal lattice structure, whereas the layers grown at TS ≈ 500 • C have a hexagonal structure and possess a ε-GaSe polytype. The latter also exhibit strong near band-edge photoluminescence at T = 300 K. The strong anisotropy of the photoluminescence intensity in an array of GaSe nanoplatelets has been revealed.
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