Application of Electron Microscopy for the detection of point defects in MBE GaAs layers grown at low temperature

Integration of GaAs devices is a challenging problem due to the lack of stable natural oxides which could isolate devices from one another. This problem is commonly solved by ion implantation, introducing point defects which can compensate impurity-related shallow donors or acceptors to make this material highly resistive. Recently, another approach was found: growing GaAs buffer layers at low temperature (∽ 200°C) removes all sidegating effects and so achieves effective device isolation. Such layers exhibit high resistivity, which is sustained even after annealing at 600°C. Own investigations by analytical electron microscopy showed these as-grown layers to be very As rich. Electron paramagnetic resonance and optical absorption studies detected AsGa antisite defects in the low-temperature buffer layers, in concentrations up to 1020 cm-3. X-ray diffraction revealed an 0.1 % increase in the lattice parameter of the epitaxial layers. After annealing at 600°C, the lattice parameter of the layers decreases to the substrate value?Transmission electron microscopy of these layers shows that their perfection is very sensitive to growth temperature and layer thickness. The layers grown below 200°C show specific defects with noncrystalline core surrounded by dislocations, stacking faults and microtwins.