Structural characterization of antimonide-based metamorphic buffer layers on (001) silicon substrate

The aim of the present study was the growth of antimony-based buffer layers with the lattice constant of InP on a GaP/Si pseudosubstrate by metal organic vapor phase epitaxy (MOVPE) and their structural investigation by atomic force microscopy (AFM), X-ray diffraction (XRD), and (scanning) transmission electron microscopy ((S)TEM). The purpose of these buffer layers was to overcome the lattice mismatch between Si and InP and to provide a smooth surface for the growth of n-doped (GaIn)As channel layers with a lattice constant of InP on a Si substrate. The growth of Sb-based buffer layers on GaP/Si pseudosubstrate is very challenging. The main problem was the island-like nucleation that occurs for Ga(PSb), Ga(AsSb) as well as GaSb on GaP/Si. The islands had different degrees of relaxation. The atomic resolution HAADF investigations have shown that the islands not only have Lomer but also 60° dislocations and 60° dislocation pairs at the interface. Additionally, they were relaxed by plastic relaxation due to the free surface as well as by the formation of stacking faults. It has been shown that the interface roughness increases for the ternary material system Ga(PSb)/GaP compared to the binary GaSb/GaP and is most severe for the Ga(AsSb)/GaP, where the group V atoms are completely exchanged from P to (AsSb). With increasing growth time, the sizes of the islands increased until they coalesced. The degree of relaxation increased with an increasing degree of coalescence. The density of stacking fault as well as threading dislocation densities were in the order of 10^10/cm^2. In addition, a low Sb-content layer that grew pseudomorphically onto GaP was observed for Ga(PSb) layers. The island-like nucleation of Ga(PSb) could neither be overcome by introducing a pseudomorphically grown Ga(PSb) interlayer with a low Sb-content between the metamorphic Ga(PSb) and the GaP layer nor by utilizing a flow rate modulated epitaxy. The most promising approach had been the introduction of an InP layer that showed a 2D-nucleation on the GaP/Si pseudosubstrate. If the growth conditions are optimized so that the relaxation of the layer will take place without the formation of lattice defects such as stacking faults or threading dislocations, the InP/GaP/Si pseudosubstrate will be a very promising growth template for the (GaIn)As channel layers