MEMORY EFFECTS ON PIEZOELECTRIC INGAAS GAAS MQW PIN DIODES/

Charge accumulation effects in piezoelectric multiple quantum well (MQ W) InGaAs/GaAs PIN diodes grown on (111)B GaAs substrates have been st udied regarding memory applications. Strain-induced piezoelectric fiel ds allow new PIN structures with configurations of negative average el ectric field (NAF) active region. These new devices can store an elect ric dipole with spatially separated electrons and holes that have low recombination probability and thus long lifetimes. This produces a lon g-range screening of the field in the active region and hence a strong blue shift of the absorption band edge (maximum light transmission fo r reading purposes). Both a light pulse and a forward voltage pulse ar e able to create the dipole (data writing or charged device). The stor ed dipole can be removed by a reverse electrical pulse (data erasing o r device discharge), resulting in a minimum light transmission across the device. Capacitance voltage and time resolved capacitance measurem ents, after single optical or electrical charging pulse at low tempera ture (20 K) have been used to determine the stored dipole behaviour. C apacitance transients analysis allowed study of the kinetics of the di scharge process, which shows a non-exponential behaviour with storage times up to 10(3) sec, suggesting very long time refresh cycles. Time resolved photocurrent has been used to check read and write capabiliti es giving on-off ratios up to 30. (C) 1997 Elsevier Science Ltd.