First observation of an extremely large-dipole infrared transition within the conduction band of a GaAs quantum well

A new type of optical transition in GaAs quantum wells has been observed. The dipole occurs between two envelope states of the conduction-band electron wave function, and is called a quantum well envelope state transition (QWEST). The QWEST is observed by infrared absorption for two structures with 65-Å-thick- and 82-Å-thick wells. The transitions exhibit resonant energies of 152 and 121 meV respectively, full width at half-maximum linewidths as narrow as 10 meV at room temperature, and an oscillator strength of 12.2. The material is anticipated to have subpicosecond relaxation times and be ideal for low-power optical digital logic.