High-resolution X-ray diffraction and electron microscopy study of porous GaAs substrates

We investigated structural perfection of porous gallium arsenide layers formed in GaAs (001). Different modes of electrochemical etching of n-type GaAs(001) substrates in fluoride-iodide aqueous electrolytes were used to form porous layers. Their structural properties were investigated by high resolution X-ray and synchrotron radiation diffraction and electron microscopy (SEM, TEM) techniques. It was shown that a single current pulse with a high magnitude forms a discontinuous porous layer with a smooth surface. Subsequent etching with a relatively low current density forms a homogeneous porous structure in the depth with approximately 30% porosity. The porous layer thickness can be varied from a few microns to several tens of microns depending on the etching time. The lattice parameter of porous GaAs layers along the surface normal is decreased by a factor of 1.5×10 -4 compared to the GaAs substrate. This contraction is related to the formation of vacancy type structural defects as revealed by the measurement of x-ray diffuse scattering.