Inducing Normally Forbidden Transitions Within the Conduction Band of GaAs Quantum Wells

Six heretofore unobserved transitions within the conduction band of a AlAs/GaAs quantum well are reported, two of which are forbidden in a symmetric quantum well. The highest energy transition is resonant with 2.86 micrometer wavelength light. These resonant energies and absorption strengths agree with predictions based on a many-body theory of an electron gas in a quantum well. A new type of infrared modulator is possible via absorption changes in the "forbidden" transition between the first and the third conduction subbands.