Inducing normally forbidden transitions within the conduction band of GaAs quantum wells

Recently, a new type of intersubband transition in GaAs quantum wells was observed by West and Eglash [1,2]. This transition differed from previous intersubband transitions [3] in that it had a direct, fully allowed, dipole between the envelope wavefunctions rather than the Bloch wavefunctions, was spectrally narrow, and temperature stable. This particular type of intersubband transition was termed a quantum well envelope subband (or state) transition “QWEST.” The Stark energy shift between the first and second conduction subbands in a GaAs quantum well was observed by Harwit and Harris [4]. Infrared detectors utilizing the QWEST have also been made [5] recently.