Wavelength dependence of the photo-electromotive-force effect in CdTe:V crystal with bipolar photoconductivity

We report on detailed investigation of the photo-electromotive-force (photo-EMF) effect in semiconductor with bipolar photoconductivity of impurity type in a spectral region close to the fundamental absorption edge, where both the photoconductivity and the photo-EMF response reach their maxima. The experiments performed with CdTe:V crystal (ΔE ≈ 1.51 eV) in the spectral range of 826–853 nm show that dynamics of the photo-EMF signal formation in this crystal is governed by relaxation of slow majority photocarriers–holes with the life-time which goes down from τ ≈ 9 μs at 850 nm to ≈6.5 μs at 826 nm. The minority photocarriers (electrons), which contribute approximately 10% of the total photoconductivity, also demonstrate significant wavelength dependence of their diffusion length with LD ≈ 8.5 μm at 850 nm and ≈6.3 μm at 830 nm. The reported results show significant improvement in responsivity of the bipolar CdTe:V photo-EMF detector when it is operated at λ = 840 nm (by factor ≈2.5 as compared with that at 852 nm).