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There is a surprising sparsity of experimental information on electron and hole impact ionisation coefficients in I n, , , , Ga, , , , As, and the only available results are in wide disagreement. In this letter, results for electron and hole ionisation coefficients, a and /l, are presented for l n, , , , Ga, , , , As. r and /l have been calculated from photocurrent gain measurements (using both mixed and pure electron injection) made on In,,,,Ga,,,,Asl l nP p-i-n structures fabricated from three separate wafers. The values for a and p are in good agreement with those found by Osaka et a / , whereas Pearsall's results are an order of magnitude higher.Optical communication systems require high-speed, lownoise detectors. Avalanche photodiodes, in which the ratio of electron and hole ionisation coefficients is large (rip > 10 [l]) would be ideal candidates for such detec-

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We report the observation of electric field induced exciton energy shifts and photoluminescence quenching in GaInAs/InP multiple quantum wells. We have measured both the photocurrent and photoluminescence spectra from 100 Å wells contained with p+- and n+-InP layers in a conventional p-i-n structure; reverse bias voltages of up to 12 V were applied. The exciton peaks in the photocurrent spectrum are seen to broaden and shift to lower energy; the photoluminescence peak, which is due to n=1 excitonic and free-carrier recombination, also shifts to lower energy and is completely quenched at high voltages. These results are similar to those reported previously for GaAs quantum wells and ascribed to the quantum-confined Stark effect.