Mid-Infrared Semiconductor Lasers based on virtual substrates with designer specified lattice-constant

半导体激光器的广泛应用极大地造福了社会，包括电信领域（用于光纤通信）、高速计算的数据传输和许多医疗治疗。然而，具有扩展功能的新型半导体激光器，如高光功率发射，低输入功率要求，以及在常用半导体材料难以进入的波长区域工作的能力，仍在研究人员的大力开发中。该计划开发的技术将提供新的商业产品机会，使半导体激光器能够在连续电流操作下以高性能运行，在技术上重要的中红外波长区域，目前难以进入。在中红外波长区域工作的高性能紧凑型光源（激光器）是远程气体传感、基于激光的测距、自由空间光通信、塑料等材料的产品标记以及医疗/牙科应用的理想选择。例如，甲烷的环境监测（遥感）代表了拟议装置的潜在大量应用，因为甲烷是辐射强迫的主要来源，其全球变暖潜势是二氧化碳的25倍。对于许多此类应用，在成本、尺寸、重量、性能和可靠性方面的实际要求使任何其他技术都无法成为可行的解决方案。技术描述：在这个项目中，我们将在变质缓冲层（MBL）衬底上开发3.0-3.5微米发射的高功率量子级联激光器（qcl）。MBL技术允许制造低应变qcl，以提供更高功率的连续波替代锑化物或ii型带间激光器，这些激光器的固有性能受到俄歇复合的限制。虽然使用传统的InP衬底已经证明了3.5微米的qcl，但有源区载流子泄漏和高材料应变已经损害了这些短波长的qcl的性能和可靠性。因此，在InP衬底上的高性能qcl的波长通常在4.5微米以上。利用非常规的超晶格（SL）材料组成（可能只在MBL衬底上），qcl将开发出足够深井，以最大限度地减少这些波长下的载流子泄漏，并降低材料应变水平，从而在3.5微米波长及以下提供优于传统方法的性能和可靠性优势。MBL技术的另一个好处是从InP基板过渡到GaAs基板，这将在制造成本和产量方面呈现出显着的优势。关键的基本问题是解决应变工程SL材料的发展应用于qcl。提出了SL结构形成在虚拟基板上的应用，极大地扩展了许多器件应用可访问的组成空间，并以一种变革性的方式解决了当前QCL技术的缺点。目前在3-3.5微米波长范围内还没有高功率单模（0.5W）半导体激光器。与目前最先进的3.0-3.5微米半导体激光器相比，建议开发3.0-3.5微米发射激光源，其相干连续波输出功率至少增加一个数量级。这种高功率设备将开辟大量新的应用，从遥感化学物质（甲烷和其他碳氢化合物）到产品（塑料）标记。提出了两种实现总体目标的新方法：(1)在3.0-3.5微米发射的量子级联激光器上实现新型阶梯锥形有源区（STA）量子级联激光器（QCL）设计，以完全抑制载流子泄漏（包括有源区间接谷泄漏），并实现从低有源区状态高效提取谐振载流子；从而获得高T0和T1值和低阈值电流；ii)使用一种新的变质缓冲层（MBL）方法来绕过应变松弛约束，从而允许生长与4.6-4.8微米QCL相同应变的QCL结构，从而具有相对较低的有源区热阻和可靠运行的电位。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Semiconductor lasers have found widespread application that greatly benefit society, including in the telecommunications field (for fiber-optic communications), data transmission for high-speed computing, and many medical therapies. However, new semiconductor lasers with extended capabilities, such as high optical power emission, lower input-power requirements, and the ability to operate in wavelength regions that are difficult to access with commonly used semiconductor materials are still under intense development by researchers. The technologies developed in this program will provide new commercial product opportunities by enabling semiconductor lasers to operate with high performance under continuous current operation, in the technologically important mid-infrared wavelength region, that is currently difficult to access. High-performance compact light sources (lasers) operating in the mid-infrared wavelength region are ideal for remote gas sensing, laser-based range finding, free-space optical communication, product marking of materials such as plastics, and medical/dental applications. A case in point, environmental monitoring (remote sensing) of methane represents a potentially large volume application for the proposed devices, since methane is a major source of radiative forcing with a global warming potential 25 times greater than CO2. For many of these applications, practical requirements in terms of cost, size, weight, performance and reliability preclude any other technology from being a viable solution.Technical description: In this program we will be developing 3.0-3.5 micron-emitting, high-power quantum cascade lasers (QCLs) on metamorphic buffer layer (MBL) substrates. The MBL technology permits the fabrication of lower-strain QCLs to provide a higher-power CW alternative to antimonide or type-II interband lasers, which are inherently performance limited by Auger recombination. Although QCLs have been demonstrated at 3.5 micron using conventional InP substrates, active-region carrier leakage and high material strain have compromised the performance and reliability of these short wavelength QCLs. Consequently, high-performance QCLs on InP substrates are typically above 4.5 micron in wavelength. Utilizing unconventional superlattice (SL) material compositions, possible only on MBL substrates, QCLs will be developed with sufficiently deep wells to minimize carrier leakage at these wavelengths and reduced material strain levels to provide performance and reliability advantages over conventional approaches at and below 3.5 micron wavelength. A further benefit of the MBL technology is the transition from InP to GaAs substrates, which will present significant advantages in terms of manufacturing cost and yield.Key fundamental issues are addressed in the development of strained-engineered SL materials for application to QCLs. The application of SL structure formation on virtual substrates is proposed which greatly expands the compositional space accessible for many device applications and addresses in a transformative way the shortcomings of current QCL technologies. There are no existing high-power single-mode (0.5W) semiconductor lasers in the 3-3.5 micron wavelength region. It is proposed to develop 3.0-3.5 micron-emitting laser sources with at least an order of magnitude increase in coherent CW output power compared to current state-of-the-art 3.0-3.5 micron semiconductor lasers. Such high-power devices will open up a plethora of new applications from remote sensing of chemicals (methane and other hydrocarbons) to product (plastics) marking. Two novel approaches are proposed to achieve the overall goal i) the implementation of novel step-tapered active-region (STA) quantum-cascade laser (QCL) designs for 3.0-3.5 micron-emitting QCLs, in order to completely suppress carrier leakage (including leakage to indirect valleys in the active region), as well as achieve efficient resonant carrier extraction from lower active region states; thus, obtaining both high T0 and T1 values and low threshold currents; ii) the use of a novel metamorphic-buffer-layer (MBL) approach to bypass the strain-relaxation constraint, thereby allowing growth of QCL structures of the same strain as 4.6-4.8 micron QCLs and thus of relatively low active region thermal resistance and potential for reliable operation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.