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Strong emission due to cold exciton formation associated with the first excited (n = 2) subband state in a GaAs quantum well is observed by spatially resolved cathodoluminescence spectroscopy, measured on the cleaved edge of the heterostructure. Origins of the enhanced (n = 2) emission are discussed based on the spatially selective carrier generation and capture and the parity-forbidden relaxation pathway of cold (n = 2) excitons into the ground exciton state. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

In this paper we show that the idea of a mid-infrared quantum-cascade laser with gain regions based on a double-phonon resonance can be implemented in the GaAs/AlGaAs system. In contrast to the usual GaAs/AlGaAs laser active region design, which involves a triple quantum well active region, here we identify an optimal heterostructure design by using a simulated annealing algorithm which is programmed to maximize the laser gain for a given wavelength and for subband spacings prescribed to satisfy the double-phonon resonance condition. The output characteristics are calculated using a full self-consistent rate equation model of the intersubband electron transport. Initial devices grown according to this design show laser action up to 240K in pulsed mode with good agreement between the calculated and measured characteristics. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]