Quantum Size Effect in Optically Active Indium Selenide Crystal Phase Heterostructures Grown by Molecular Beam Epitaxy
Indium selenide attracts the interest due to its outstanding electronic and optical properties which are potentially prospective in view of applications in electronic and photonic devices. Most of the polymorphic crystal phases of this semiconductor belong to the family of two-dimensional van der Waals semiconductors. In this study optically active indium selenide crystal phase heterostructures are fabricated by molecular beam epitaxy in a well-controlled manner. It is demonstrated that by changing the growth conditions one may obtain either {\gamma}-InSe, or {\gamma}-In2Se3, or \b{eta}-yIn2Se3 crystal phases. The most promising crystal phase heterostructures from the point of view of photonic applications is found to be the {\gamma}-InSe/{\gamma}-In2Se3 heterostructure. An intense optical emission from this heterostructure appears in the near infrared spectral range. The emission energy can be tuned over 250 meV by changing {\gamma}-InSe layer thickness which is explained by the quantum size effect. The optically active indium selenide crystal phase heterostructures represent, therefore, an interesting platform for the design of light sources and detectors in the near infra-red. The use of molecular beam epitaxy for this purpose ensures that the structures are fabricated on large surfaces opening the possibility for the design of device prototypes by using lithography methods