Carrier-sign reversal in Bi-doped bulk amorphous semiconductors Ge<SUB>2</SUB>Te<SUB>80-x</SUB>Bi<SUB>x</SUB>

A p-n transition in the electronic conduction in Bi-doped bulk amorphous semiconductors Ge<SUB>2</SUB>Te<SUB>80-x</SUB>Bi<SUB>x</SUB> at about x=3.5 has been observed for the first time. n-type conduction has been established by the measurement of thermoelectric power that becomes negative at x~3.5. Measurement of the electrical transport under high quasihydrostatic pressure (p≤ 120 kbar) has also been studied in x=0,2,3,4,6 compositions. Electrical resistivity (ρ ), thermal activation energy (Δ E), and (dlog<SUB>10ρ</SUB>/dp) show a sudden drop in their values in the ρ -n transition region (x=3-4). Results are discussed in the light of Phillip's model of microclusters and constraint theory