Development of high-performance InAs quantum cascade lasers

为了开发低阈值电流密度、高功率和高温的量子级联激光器，我们采用分子束外延的方法制备了基于inas的量子级联激光器，并研究了激光器的特性，特别是它们与有源区能带结构的关系。我们利用InAs/Al_<0.2>Ga_<0.8>Sb超晶格活性层，在液氮温度下实现了低阈值电流密度（0.4 kA/cm^2）的工作。发射波长为10 μm，与设计波长基本一致。这是在中红外光谱区域工作的qcl的最低阈值电流密度之一。我们演示了发射波长为8.9 μm的基于inas的qcl的室温操作。为了减少有源层的热载流子泄漏，采用了对角子带间跃迁。300 K时的阈值电流密度为12.0 kA/cm^2，最高工作温度为305 k3。为了增大操作电流的动态范围，采用了提高注入层掺杂浓度的方案。观察到的室温阈值电流密度为4.0 kA/cm^2，是基于inas的qcl中最低的阈值电流密度。我们证明了在液氮温度下的输出光峰值功率大于1 W，在室温下的输出光峰值功率大于125 mW。研究了结构对光增益系数的依赖关系及其对最大工作温度的影响。我们发现具有最大光学增益系数的有源层具有最高的工作温度。观察到的最高工作温度为+100℃，这是基于inas的qcl的最高工作温度。

In order to develop low-threshold current density, high-power and high-temperature quantum-cascade lasers (QCLs), we fabricated InAs-based QCLs by molecular beam epitaxy and investigated laser characteristics, especially their relationship with the band structure of an active region. The summary of the research results is as follows:1、Low-threshold current density operationWe demonstrated low-threshold current density (0.4 kA/cm^2) operation at liquid-nitrogen temperature by employing InAs/Al_<0.2>Ga_<0.8>Sb superlattice active layers. The emission wavelength was 10 μm, which was in close agreement with the designed wavelength. This is among the lowest threshold current density of QCLs operating in the mid-infrared spectrum region.2、Room-temperature operationWe demonstrated the room-temperature operation of InAs-based QCLs emitting at 8.9 μm. In order to decrease thermal carrier leakage from the active layer, a diagonal intersubband transition was used. The observed threshold current density at 300 K was 12.0 kA/cm^2 and maximum operation temperature was 305 K.3.High-power operationIn order to increase the dynamic range of the operation current, a scheme to increase the doping concentration in the injection layers was employed. The observed room-temperature threshold current density was 4.0 kA/cm^2, which is the lowest threshold current density in InAs-based QCLs. We demonstrated the output optical peak power above 1 W at liquid-nitrogen temperature and 125 mW at room-temperature.4.High-temperature operationStructure dependence on optical gain coefficient and its influence on the maximum operation temperature were investigated. We found that the active layer which exhibits the maximum optical gain coefficient presents the highest operation temperature. The observed maximum operation temperature was +100 ℃, which is the highest operation temperature in InAs-based QCLs.