Interface Raman Modes to Study Compositional Intermixing in GaAs/AlAs Superlattice

摘要

Quantum-well intermixing (QWI) technologies have become a strong contender for the realization of photonic integrated circuits. These technologies are now widely applied in devices such as laser diodes integrated with passive sections and in all optical switch matrices. It has been demonstrated that QWI enables the tailoring of the bandgap and hence the linear and nonlinear optical coefficients of these structures with sufficient accuracy for the realization of functional devices. In novel applications, QWI can be used to modulate the third order susceptibility coefficient χ{sup}(3) for all optical switching devices, or the second order susceptibility coefficient χ{sup}(2) to achieve quasi-phase-matching (QPM) for efficient optical frequency conversion in compound semiconductors. However, to enable efficient QPM devices, further optimization of the QWI process parameters such as implantation dose, and energy as well as annealing conditions is needed. To this end, we aim to develop micro-Raman for non-destructive characterization of semiconductor heterostructures, with a particular focus on intermixing in GaAs/AlAs SL structures. Raman offers improved spatial resolution over PL because it is not influenced by carrier diffusion. It also provides considerable structural information, potentially detecting variations in lattice order, stress, and composition. Further, unique modes appear in the Raman spectra of short SL which may reveal SL structure. These include interface (IF) modes which arise due to coupling between the standing electric potential in the SL and the optic phonons. IF modes depend sensitively on the layer thickness and the interface quality between the superlattice layers. For QWI materials we can use these unique Raman peaks to characterize the material and relate the results to the degree of intermixing along the grating.