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Agata Jasik,Iwona Sankowska,Andrzej Wawro,Jacek Ratajczak,Dariusz Smoczyński,Krzysztof Czuba 한국물리학회 2019 Current Applied Physics Vol.19 No.4
We report on the growth of fully relaxed and smooth GaSb layers with reduced density of threading dislocations, deposited on GaAs substrate. We prove that three parameters have to be controlled in order to obtain applicable GaSb buffers with atomically smooth surface: interfacial misfit (IMF), the etch pit density (EPD) and the growth mode. The GaSb/GaAs interfacial misfit array and reduced EPD ≤1.0×107 cm−2 were easily obtained using Asflux reduction for 3 min and Sb-soaking surface for 10 s before the GaSb growth initiation. The successive growth of GaSb layer proceeded under the technological conditions described by the wide range of the following parameters: rG ∈ (1.5 ÷ 1.9) Å/s, TG ∈ (400 ÷ 520)°C, V/III ∈ (2.3 ÷ 3.5). Unfortunately, a spiral or 3D growth modes were observed for this material resulting in the surface roughness of 1.1 ÷ 3.0 nm. Two-dimensional growth mode (layer by layer) can only be achieved under the strictly defined conditions. In our case, the best quality 1-μm-thick GaSb buffer layer with atomically smooth surface was obtained for the following set of parameters: rG=1.5 Å/s, TG=530 °C, V/III=2.9. The layer was characterized by the strain relaxation over 99.6%, 90° dislocations array with the average distance of 5.56 nm, EPD ∼8.0×106 cm−2 and 2D undulated terraces on the surface with roughness of about 1 ML. No mounds were observed. We belive that only thin and smooth GaSb layer with reduced EPD may be applied as the buffer layer in complex device heterostructures. Otherwise, it may cause the device parameters deterioration.
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A. Jasik,I. Sankowska,J. Ratajczak,A. Wawro,D. Smoczyński,K. Czuba,M. Wzorek 한국물리학회 2019 Current Applied Physics Vol.19 No.2
In the paper, the comparative analysis of type-II InAs/GaSb SLs deposited on three types of GaSb buffers: homoepitaxial, metamorphic and one grown using the interfacial misfit (IMF) array technique has been presented. The buffer layers as well as superlattices were grown under nominally identical technological conditions. HRXRD investigations proved better crystal quality of the metamorphic material than the IMF-GaSb. FWHMRC were equal to 156 arcsec and 196 arcsec, respectively. The surface roughness of about 1 ML and 4 MLs was obtained using the atomic force microscope for 4.0 μm–metamorphic GaSb and 1.5 μm-IMF-GaSb layers, respectively. The etch pits density for both buffers was similar, 1–2 × 107 cm−2. Superlattice with 500 periods deposited on the homoepitaxial buffer was used as a reference of the best crystal quality. HRTEM images revealed straight InAs/GaSb interfaces with 1 ML thicknesses in this sample. The interfaces in SL deposited on IMFGaSb buffer were undulated and smeared over 3 MLs. The use of the metamorphic buffer resulted in 1–2 ML straight InAs/GaSb interfaces. The main reason for this is the roughness of IMF-GaSb buffer with mounds on the surface. Based on the obtained results we have demonstrated the advantage of metamorphic approach over IMF growth mode in GaSb/GaAs material system. A two times thicker buffer could be the price worth paying for high quality structures, even when working in the production mode.
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