The extended wavelength InGaAs material (2.3 μm) was prepared by introducing compositionally undulating step-graded InAs_yP_1−y buffers with unequal layer thickness grown by solid-source molecular beam epitaxy (MBE). The properties of the extended wavelength InGaAs layer were investigated. The surface showed ordered crosshatch morphology and a low roughness of 1.38 nm. Full relaxation, steep interface and less than one threading dislocation in the InGaAs layer were demonstrated by taking advantage of the strain compensation mechanism. Room temperature photoluminescence (PL) exhibited remarkable intensity attributed to the lower density of deep non-radiative centers. The emission peak energy with varied temperatures was in good agreement with Varshni’s empirical equation, implying high crystal quality without inhomogeneity-induced localized states. Therefore, our work shows that compositionally undulating step-graded InAsP buffers with a thinner bottom modulation layer, grown by molecular beam epitaxy, is an effective approach to prepare InGaAs materials with wavelengths longer than 2.0 μm and to break the lattice limitation on the materials with even larger mismatch.

The low-temperature-grown InGaAs (LT-InGaAs) photoconductive antenna has received great attention for the development of highly compact and integrated cheap THz sources. However, the performance of the LT-InGaAs photoconductive antenna is limited by its low resistivity and mobility. The generated radiated power is much weaker compared to the low-temperature-grown GaAs-based photoconductive antennas. This is mainly caused by the low abundance of excess As in LT-InGaAs with the conventional growth mode, which inevitably gives rise to the formation of As precipitate and alloy scattering after annealing. In this paper, the migration-enhanced molecular beam epitaxy technique is developed to grow high-quality (InAs)_m/(GaAs)_n short-period superlattices with a sharp interface instead of InGaAs on InP substrate. The improved electron mobility and resistivity at room temperature (RT) are found to be 843 cm²/(V·s) and 1648 ohm/sq, respectively, for the (InAs)_m/(GaAs)_n short-period superlattice. The band-edge photo-excited carrier lifetime is determined to be ~1.2 ps at RT. The calculated photocurrent intensity, obtained by solving the Maxwell wave equation and the coupled drift–diffusion/Poisson equation using the finite element method, is in good agreement with previously reported results. This work may provide a new approach for the material growth towards high-performance THz photoconductive antennas with high radiation power.

The atomic structure and surface chemistry of GaP/Si(100) heterostructure with different pre-layers grown by molecular beam epitaxy are studied. It is found that GaP epilayer with Ga-riched pre-layers on Si(100) substrate has regular surface morphology and stoichiometric abrupt heterointerfaces from atomic force microscopes (AFMs) and spherical aberration-corrected transmission electron microscopes (ACTEMs). The interfacial dynamics of GaP/Si(100) heterostructure is investigated by X-ray photoelectron spectroscopy (XPS) equipped with an Ar gas cluster ion beam, indicating that Ga pre-layers can lower the interface formation energy and the bond that is formed is more stable. These results suggest that Ga-riched pre-layers are more conducive to the GaP nucleation as well as the epitaxial growth of GaP material on Si(100) substrate.