Combined local and carrier transport optical nonlinearities in a hetero n-i-p-i structure

Nonlinear optical effects have been measured in a novel hetero n-i-p-i structure with strained InAs/GaAs superlattices as the quantum wells. For intensities below 6 W/cm², changes in transmission are observed due to the screening of built-in fields in conjunction with the quantum-confined Stark effect. For intensities greater than 30 W/cm², a further increase in transmission is observed due to state filling and exciton screening in the wells. It is demonstrated that a n-i-p-i structure, because of its lengthened carrier lifetime, can be used to reduce the intensity necessary for exciton saturation and state filling in quantum wells when the wells are placed in the i regions. Total changes in transmission greater than 25% have been seen, with no sign that the nonlinearity is saturating at 1 kW/cm² (the highest excitation used here).