Infrared Semiconductor Laser by Subband Transition at 3μmwavelength Band

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Lasing wavelength in semiconductor lasers between 2.5 and 4μm at room temperature has not been achieved yet so far. We have proposed a novel structure of a quantum cascade laser (QCL) to get the wavelengths. The structure is based on the AlInAs/GaInAs superlattice lattice matched to the InP substrate. Some of the AlInAs layers in the active quantum well layers are replaced by AlAsb and AlAs layers, with the conduction band offsets to the GaInAs well are 1.60 and 1.06eV, respectively, which is substantially larger than that of AlInAs, 0.52eV. These higher barriers prevent the electron overflow in the active quantum wells and enable it to attain the shorter lasing wavelength. We have also proposed a injectorless QCL to reduce the number of quantum well layers and improve the quantum efficiency for the 3μm wavelength band.Layer structures are designed by a numerical computer simulation developed for the structure. For example, two AlAsSb barriers and one AlAs barrier in the 4 quantum wells for the active layers is designed and have been indicated to be able to get the lasing wavelength less than 3μm. A injectorless structure at 3.2μm aimed for detection of CH_4 has also been designed.The growth conditions of AlInAs, GaInAs, AlAsSb lattice-matched to InP at same substrate temperature are investigated by adjusting the metal source flux from cells by precisely controlled cell heater temperature. The cell for Sb is a cracking type to get Sb_2 in spite of Sb_4, to improve the crystal quality. The lattice match condition has been measured by XRD. It is confirmed by the photoluminescence that the AlAsSb layer crystal quality has been remarkably improved with Sb_2 source.Layer structure of the conventional AlInAs/GaInAs cascade structure at 5.4μm and AlAsSb/GaInAs cascade structure at 3.2μm grown by MBE, and confirmed the thickness of each layer is precisely controlled within a monolayer by TEM observation.