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The effect of high polaron concentration on the polaron transport in NbO 2.5-x : optical and electrical properties

1988; IOP Publishing; Volume: 21; Issue: 20 Linguagem: Inglês

10.1088/0022-3719/21/20/009

1747-3802

Claus H. Rüscher, Ekhard K. H. Salje, Altaf Hussain,

Semiconductor materials and devices

The electrical conductivity and optical absorption of NbO2.5-x (0.005<x<0.08) are described by polaron ground states. Correlated hopping and polaronic absorption of weakly disordered systems are observed in the regime of low carrier concentration (x<0.05). Bipolarons and single polarons are both stable in this regime. At higher carrier concentrations, quasi-metallic conductivity and saturated polaron concentrations are described as being due to the superposition of polaron groundstates and quasi-free electrons. The saturation concentration yields a critical distance of about 10 AA between polarons. The threshold value of x=0.05 is related to the geometrical properties of the NbO2.5-x structures.