Abstract
AbstractWe report the first observation of optically pumped spontaneous emission from intersubband transitions by elec- trons in an n-type GaAs/A1GaAs coupled-quantum-well structure. Electrons were pumped from the first to fourth con- duction subbands with a CW CO2 laser operating at a photon energy of 133 meV. The transition from the fourth to the third subbands occurred at an energy of 17 meV and had a full width at half-maximum of 3 meV. 1. IntroductionThere is growing interest in new optical devices based on confined states in quantum wells. Intersubband transi-tions are of special interest because they can be designed to occur over most of the far- and mid-infrared spectrum.17Our research is aimed at determining whether the quantum-well intersubband transitions can be used as a source ofcoherent radiation in the far-infrared. Electrically pumped spontaneous emission from transitions between conductionsubbands in isolated quantum wells has been observed by Helm et al. by electrically heating the electrons in a widequantum well.1'2 We describe here the first observation of spontaneous intersubband emission from carriers in a
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