Optical Second-Harmonic Generation from Unbiased Single Ga1-xAlxAs Quantum Wells with Symmetric Structures

Nonlinear optical susceptibilities of various quantum-well Ga1-xAlxAs compounds grown by molecular beam epitaxy are measured by pumping with a Q-switched and mode-locked Nd: YAG laser. The contribution of second-harmonic waves from the bulk nonlinear susceptibility and the electrical dipole sheet in the quantum well is also calculated separately. The measured second-harmonic reflectivity decreases as the silicon doping concentration increases and its angular variation follows the Bloembergen and Pershan (BP) theory. Both the experimental and theoretical results indicate that the electron gas and dipole sheet in the unbiased single quantum wells have a negligible effect on the second-order nonlinear generation.