(11 IOTA)-Oriented Heterostructures and Devices: The Effects of Strain and Orientation

Abstract

Abstract : The broad objective on this project is to investigate the unique optical and optoelectronic properties of 110, 111 and 112-oriented multiple quantum wells (MQW's) and to study the ways in which strain and external optical fields can introduce crystallographic dependences to the optical properties of otherwise isotropic materials. Toward this end, we have demonstrated that dual-channel spectral interferometric techniques can be used to measure the amplitude, phase and polarization state of extremely weak ultrafast coherent emission from MQW's. The vectorial dynamics of the coherent four-wave mixing emission are found to exhibit systematic variations with excitation fluence, time delay between incident pulses, the tuning of the laser wavelength, and the orientation of the input polarizations. This time-dependent polarization state indicates that the pump pulses have induced dynamic anisotropies in the sample. From these anisotropies, a self consistent picture of the excitonic and carrier dynamics is obtained that delineates the roles of the various many body effects. These studies demonstrate that time-resolved polarimetry is an extremely sensitive way to study many body effects and that the vectorial dyanmics contain essential information about quantum interference and optical anisotropies that would be difficult to obtain in any other way. This should make these techniques extremely useful in probing strained MQW's and semiconductors grown in unconventional directions, such as quantum dots. In addition, we are now using the coherent anisotropies and many body vectorial dynamics studied here to make high-speed high-contrast polarization sensitive modulators.