INFLUENCE OF CLUSTER STRUCTURE ON THE THERMAL-STABILITY OF AMORPHOUS CDGEAS2[NI] FILMS AND DOPING EFFECTIVENESS

High-temperature electrical conductivity measurements were used to cha racterize the cluster structure and thermal stability of amorphous CdG eAs2(Ni) films. At Ni contents below 2 wt %, the electrical behavior o f the amorphous CdGeAs2 films is dominated by hopping conduction throu gh impurity centers forming in the disordered glass matrix. The concen tration of these centers depends on the concentration of intrinsic def ects and constitutes less than 1% of the total impurity concentration. More than 99% of the number of Ni atoms are accommodated by impurity clusters. Our results provide evidence for nonuniform distribution of Ni impurity. The reduction in sigma at low Ni concentrations is associ ated with the decrease of Ni solubility in the disordered glass matrix , in which separate impurity centers responsible for hopping conductio n are formed. At high Ni concentrations, conductivity is of a percolat ion nature owing to the overlap of impurity clusters and the formation of a continuous conducting path through metallic regions. As a result , conductivity rises during heat treatment.