Electrical conductivity of disordered layers in GaAs crystal produced by ion implantation

Abstract

The electrical conductivity of disordered layers in GaAs produced by ion implantation has been studied as a function of ion species, dose level, energy of implanted ions, and anneal temperature. The resistivity of the implanted layer, ρ, at room temperature can be expressed by a single relation, ρ=const×NDD−3, even for different masses and energies of implanted ions, where NDD is the total number of displacements of host atoms per unit volume due to nuclear collisions with implanted ions. At a temperature above 180 K the resistivity is proportional to exp(B/T) and below 180 K it changes as exp(B/T1/4). The conduction mechanism of the implanted layers is discussed based upon the hopping conduction in disordered or amorphous semiconductors. The annealing behavior of the implanted layers was also studied. The activation energy for recovery of the resistivity ρ was about 0.35 eV, which is quite small compared with the migration energies of stray atoms in ordered crystals. These results indicate that the implanted layer is in a disordered state rather than in a crystalline state containing the point defects.