Transient photoconductivity in Ge:Be due toBe+formation

The effect of the formation of the overcharged Be acceptor center, ${\mathrm{Be}}^{+}$, on transient photoconductive response has been studied in Ge:Be. The response of the photocurrent to step-function changes in photon backgrounds (λ=40 μm) is dominated by a slow transient with time constants on the order of 0.1–1.0 s at temperatures of 2–3 K. The activation energy of the hole-trapping phenomenon has been measured to be 4.3 meV. Application of 9.8×${10}^8$ dyn/${\mathrm{cm}}^2$ uniaxial stress, sufficient to eliminate ${\mathrm{Be}}^{+}$ formation, also eliminates the slow-transient response. Modeling of the transient response, in a unipolar system where the trapping mechanism is assumed to be hole trapping by ${\mathrm{Be}}^0$, results in good agreement with the experimental results.