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

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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.