Growth of the BaF2/CaF2/A12O3 Structures for the Radiation-Resistant Photodetectors for Infrared Range

A study of the surface morphology of epitaxial layers in «BaF
2
/CaF
2
/Al
2
O
3
system» grown by molecular beam epitaxy technique on sapphire substrates was carried out by atomic force microscopy. The growth was performed in a closed technological cycle on the sapphire substrates with (0112) orientation and was controlled by reflection high-energy electron diffraction technique. Analysis of the diffraction pattern showed that the initial stage of growth of the calcium fluoride layer is observed layer-by-layer growth. With an increase in the thickness of the film, the rods in the diffraction pattern are transformed into spots, indicating that the two- dimensional growth mechanism is replaced by a three- dimensional growth mechanism. The average height of microroughnesses of the calcium fluoride surface was about 33 nm. In order to improve the surface morphology of the heterostructures of calcium fluoride on sapphire, annealing was used. Then, a barium fluoride layer was deposited on the surface of this heterostructure. Analysis of the surface morphology by atomic force microscopy showed that there was an improvement in a surface morphology. These buffer layers can be used to overcome a mismatch on the lattice constant between the sapphire substrate and the photosensitive semiconductor layer of the IV-VI type and solid solutions on their basis. The buffer layers will reduce the mechanical stresses that arise in the heterostructure due to the mismatch between the thermal expansion coefficient of the photodetector film and sapphire substrate.