Optical and electrical properties of alkaline-doped and As-alloyed amorphous selenium films

Electrical and optical properties Cs-doped a-Se_0.95As_0.05 (stabilized a-Se that has been alloyed with As) have been investigated. As expected there was no electron paramagnetic resonance signal on Cs-doped films or bulk samples, which put the spin-active defect concentrations below 10¹⁵ cm⁻³. The Cs-addition to a-Se_0.95As_0.05, leads to the n-type doping of a-Se_0.95As_0.05 in the sense that the undoped material has μ_hτ_h>> μ_eτ_e whereas the alkaline doped material has μ_eτ_e>> μ_hτ_h. The Cs addition also leads to a reduction of the refractive index n and a reduction of the glass transition temperature T_g, and affects the temporal relaxation behavior of a-Se film thickness after annealing and sequential quenching. We have measured the refractive index dispersion, n(λ) versus λ, bandgap (E_g) and Urbach width (ΔE) for undoped and Cs-doped films at room temperature and at a temperature just below the glass transition temperature. The photoluminescence (PL) experiments confirm earlier experiments that the PL emission is a broad emission spectrum with a significant Stoke’s shift following roughly the ~ E_g/2 empirical rule. The present work confirms that Cs-doped and As-stabilized a-Se is n-type.