Infrared Semiconductor Laser by Subband Transition at 3μmwavelength Band

半导体激光器在室温下的激光波长在2.5 ~ 4μm之间，目前还没有实现。我们提出了一种新的量子级联激光器（QCL）结构来获得波长。该结构基于与InP衬底匹配的AlInAs/GaInAs超晶格。主动量子阱层中的部分AlInAs层被AlAsb和AlAs层所取代，其导带对GaInAs的偏移量分别为1.60和1.06eV，比AlInAs的0.52eV要大得多。这些较高的势垒防止电子在有源量子阱中溢出，使其能够获得较短的激光波长。为了减少量子阱层数，提高3μm波段的量子效率，我们还提出了一种无注入器的量子阱结构。采用计算机数值模拟的方法设计了层状结构。例如，在有源层的4个量子阱中设计了2个AlAsSb势垒和1个AlAs势垒，并表明它们能够获得小于3μm的激光波长。设计了一种用于检测CH_4的3.2μm无喷射器结构。通过精确控制电池加热器温度，调节电池金属源通量，研究了与InP匹配的AlInAs、GaInAs、AlAsSb晶格在相同衬底温度下的生长条件。Sb的晶胞为裂化型，在Sb_4存在的情况下得到Sb_2，以提高晶体质量。用XRD测定了晶格匹配条件。光致发光结果表明，Sb_2源明显改善了AlAsSb层的晶体质量。通过MBE生长出了常规AlInAs/GaInAs级联5.4μm结构和AlAsSb/GaInAs级联3.2μm结构的层状结构，并通过TEM观察证实了每层的厚度都精确控制在单层内。

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.