DISPLACEMENT PHOTOCURRENTS AND SCREENING EFFECTS IN NOVEL PIEZOELECTRIC INGAAS GAAS MULTIPLE-QUANTUM-WELL P-I-N-DIODES/

Room-temperature time-resolved photocurrent measurements have been per formed on novel InGaAs/GaAs multiple-quantum-well (MQW) P-I-N diodes o n (111)B GaAs substrates, having an average electric field of opposite sign to the built-in field. Direct evidence for dipole formation, dis placement photocurrents and out-of-well screening by photocarriers is found. In these piezoelectric structures the sign of the internal fiel d can be controlled by an external modulating voltage and the opticall y pumped charges stored at the extremes of the diode MQW active region can be extracted by appropriate pulsed biasing. The generated dipole moment and its time evolution have been determined by an optical pump and electrical probe technique: the spatial separation of electrons an d holes accounts for the observation of slow recombination processes. The piezoelectric constant is evaluated for InxGa1-xAs (x = 17% In) fr om the zero-average-field condition.