Abstract
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.