Electrical inhomogeneity in 1" diameter partially dislocation-free undoped LEC GaAs

Abstract

The influence of dislocations on the electrical properties of 1" partially dislocation-free LEC GaAs has been studied as a function of the fraction of melt solidified (g). Microscopic electrical characterisation was performed using spreading resistance and anodisation imaging techniques, and Hall measurements at 294-400 K were employed for macroscopic characterisation. The zero-dislocation-density seed end regions are microscopically uniform with consistently high mobility, resistivity and thermal activation energy. However, dislocated regions are microscopically non-uniform with lower mobilities and activation energies. At g>0.4, carrier concentrations increase due to the presence of a shallow donor, possibly at Ec-0.42 eV, at the dislocations, and this causes large microscopic fluctuations in resistivity. Radial dependences of the electrical parameters vary with dislocation distribution and sub-structure along the crystals, with the mobility having an 'M' shaped radial variation at g=0.5 where dislocations lie in slip bands and a 'W' shape at g approximately 0.97 where the resistivity is low and dislocations form cellular networks. Good correlation of electrical inhomogeneity with slip bands, cell structure and lineage on a microscopic scale is obtained.