Intersubband quantum cascade electroluminescent device with self-organized In/sub 0.4/Ga/sub 0.6/As/GaAs quantum dot active region

Self-organized quantum dots have been used with great success in quantum dot infrared photodetectors (QDIPs), wherein intersubband transitions between confined electron states are utilized. From femtosecond differential transmission spectroscopy, it has been established that at higher temperatures, excess electrons preferentially occupy the excited dot states and wetting layer states. The discrete energy levels in quantum dots lead to reduced phonon coupling and promise high-temperature operation of intersubband devices. Additionally, quantum dots promise normal incidence operation and surface emission, large tunability of emission (or absorption) wavelength and polarization-selective operation. These attributes make self-organized quantum dots very attractive for the realization of intersubband surface-emitting infra-red light sources for the 3-24 /spl mu/m wavelength range. Intersubband luminescence from quantum dots has previously been demonstrated from single dot layer devices. We report here the design and properties of surface-emitting InGaAs/GaAs quantum dot infrared electroluminescent device in a quantum cascade design. Novel use of a dilute nitride GaAsN/GaAs chirped superlattice in the cascade design has allowed us to demonstrate the longest wavelength (/spl sim/20 /spl mu/m) unipolar quantum dot electroluminescence to date and the first viable solution to strain build-up in quantum dot cascade lasers.