EXTERNAL BIAS VOLTAGE AND INCIDENT LIGHT-INTENSITY DEPENDENT EFFECTS OF QUANTUM-CONFINED EXCITONIC TRANSITIONS ON BULK BACKGROUND PHOTOCURRENT SPECTRA

An experimental investigation of the unique photocurrent spectra of p- i-n photodiode with a GaAs/AlAs/AlGaAs quantum well and bulk GaAs abso rption regions at 77 K is presented. The results showed that the excit onic absorption transitions in the quantum wells create sharp dips in the featureless bulk background spectra for low reverse bias voltages, while the spectra at high reverse biases show normally expected featu res with sharp quantum-confined excitonic absorption peaks superimpose d on the background absorption. Furthermore, we found that the spectra l features are very sensitive to the incident light intensity. These r emarkable results are explained in terms of competition between the ca rrier escape rate from the quantum well region and the carrier generat ion rate in the bulk GaAs region, as well as by partial screening indu ced by carriers accumulated in the quantum well region.