A comprehensive investigation of the interfacial misfit (IMF) array formation has been carried out. The studies were based on the static phase diagram for GaAs (001) surface and As 2 dimers on the surface. Prior to the initiation of the GaSb growth two attempts of the temperature decreasing were performed: before and after the GaAs termination. The GaAs was grown in the optimal conditions for GaSb material. The influence of the interruption time on GaSb/GaAs heterostructure parameters was examined. Two cases were investigated: with and without Sb-soaking of the GaAs surface. The periodic array of edge dislocations at GaSb/GaAs interface was confirmed using Burger's circuit theory. Careful examination of misfit surroundings revealed one uncompleted Burger's vector that indicated one dislocation of mixed type among eight of the edge type. The distance between lattice sites of dislocations was 5.51 nm on average. The crystal quality of 5.0 µm GaSb layer was characterized by FWHM 2θ/ω = 42 arcsec, FWHM RC = 125 arcsec. The EPD = 4 × 10 6 cm − 2 was estimated after etching in FeCl 3 :HCl solution. The Δq z /Δq x ratio of 0.60 for 5.0 µm GaSb layer was higher than for 2.5 µm GaSb layer of 0.59. The probable reason was the thickness-dependent 60° dislocation density. The electrical parameters measured for 2.5 µm GaSb were: p = 4.0 × 10 16 cm −3 (2.0 × 10 16 cm −3 ) and µ = 599 cm 2 /V s (3420 cm 2 /V s) at 300 K (77 K).

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The Al 0.45 Ga 0.55 As/In x Ga 1Àx As active regions in quantum cascade laser structures grown on (001) GaAs substrates were investigated using the highresolution X-ray diffraction method. The onset of the strain relaxation process has been studied. Reciprocal-space mapping showed that diffuse scattering is visible in the early stage of relaxation for the structure with x = 2.64% in the In x Ga 1Àx As layers. It has been proved that the diffuse scattering is the result of misfit dislocations generated by partial relaxation of the structures. The integration of the diffuse scattering has enabled determination of the dislocation density.

Doping of the absorption region is one of the most crucial aspects in the narrow-bandgap semiconductor design of a photodiode, especially if it is adjacent to the p-n junction area. It has a significant impact on various dark current mechanisms, and thus the overall performance of these devices. In this work, the influence of Be doping placement in the absorption region of type-II InAs/ GaSb superlattice-based homojunction photodiodes on their performance was investigated. The analysis of diffusion, generation-recombination, shunt and the tunnelling components of the dark current was performed over a wide range of temperatures. Moreover, performance-limiting factors were considered as well as their impact on the most important figures of merit of the photodetectors. The photodiodes with Be-doped InAs layers in the absorption region achieved the best performance.