We observed lattice distortions in liquid encapsulated Czochralski (LEC)-grown GaAs crystals by double crystal reflection topography. A large variation of lattice orientation due to dislocations was observed in undoped GaAs crystals and at slippage from the wafer periphery in In-doped GaAs crystals, while a large variation of lattice spacing was observed in In-doped GaAs crystals.
We have developed a wafer-scale layer-transfer technique for transferring GaAs and Ge onto Si wafers of up to 300 mm in diameter. Lattice-matched GaAs or Ge layers were epitaxially grown on GaAs wafers using an AlAs release layer, which can subsequently be transferred onto a Si handle wafer via direct wafer bonding and patterned epitaxial lift-off (ELO). The crystal properties of the transferred GaAs layers were characterized by X-ray diffraction (XRD), photoluminescence, and the quality of the transferred Ge layers was characterized using Raman spectroscopy. We find that, after bonding and the wet ELO processes, the quality of the transferred GaAs and Ge layers remained the same compared to that of the as-grown epitaxial layers. Furthermore, we realized Ge-on-insulator and GaAs-on-insulator wafers by wafer-scale pattern ELO technique.
Control of the crystal phases of GaAs nanowires (NWs) is essential to eliminate the formation of stacking faults which deteriorate the optical and electronic properties of the NWs. In addition, the ability to control the crystal phase of NWs provides an opportunity to engineer the band gap without changing the crystal material. We show that the crystal phase of GaAs NWs grown on GaAs(111)B substrates by molecular beam epitaxy using the Au-assisted vapor–liquid–solid growth mechanism can be tuned between wurtzite (WZ) and zinc blende (ZB) by changing the V/III flux ratio. As an example we demonstrate the realization of WZ GaAs NWs with a ZB GaAs insert that has been grown without changing the substrate temperature.
The n-type doping of (Al)GaAs grown on GaAs using silicon (Si) was studied in metal-organic vapour-phase epitaxy using reflectance anisotropy spectroscopy. The reflectance anisotropy (RA) of GaAs was measured on undoped layers and on layers with increasing Si n-type doping concentrations up to 1 × 1020 cm−3. It was found that the RA still changes even though the carrier concentration stays constant and only the Si concentration in the crystal lattice is increasing at values above 5 × 1018 cm−3. The doping dependence of the RA of AlxGa1−xAs layers up to aluminium concentrations of x = 0.7 is similar to the GaAs case with an increasing amplitude while for highly doped AlAs it is slightly different. While the broad peak in the RA spectra around 3.9 eV of Si-doped GaAs and AlxGa1−xAs up to x = 0.7 shows a steady decrease with increasing doping concentration the RA of AlAs in this spectral region shows a shift of the peak towards lower photon energies and an increase in amplitude for doping concentrations above 2 × 1018 cm−3. Finally, the temperature dependence was studied for Al0.5Ga0.5As showing that the influence of the doping on the RA spectra is decreasing with increasing temperature..