TERAHERTZ QUANTUM CASCADE LASER UTILIZING LATTICE-MATCHED III-NITRIDE HETEROSTRUCTURES

Purdue University, West Lafayette IN

Investigators

Abstract

TERAHERTZ QUANTUM CASCADE LASER UTILIZING LATTICE-MATCHED III-NITRIDE HETEROSTRUCTURES Michael J. Manfra and Oana Malis, Purdue University III-nitride semiconductors have unique electronic properties that make them promising for extending the functionality of semiconductor light sources into spectral ranges currently inaccessible with other material systems. We propose to demonstrate and investigate a new class of far-infrared semiconductor lasers emitting in the 1-10 THz range (30-300 ìm wavelength range). These lasers will utilize intersubband transitions in the conduction band of lattice-matched III-nitride heterostructures and employ the general operating principles of quantum cascade lasers (QCLs). Our novel approach involves using low Al-composition, lattice-matched quaternary nitrides (AlInGaN/GaN) and high quality quasi-bulk GaN substrates to mitigate material quality issues that have hampered progress of nitride intersubband devices in the past. Our choice of lattice-matched heterostructures has the additional advantage of eliminating the effect of piezoelectric fields at hetero-interfaces, therefore facilitating conduction band engineering. To completely remove polarization discontinuities at hetero-interfaces, laser structures will also be grown on non-polar GaN substrates. The research effort will be interdisciplinary and will involve material design and growth, structural characterization, device fabrication, and device testing. Intellectual merit: This project investigates the feasibility of a new class of semiconductor lasers to fill the underutilized THz gap that is currently inaccessible with any other semiconductor technology. If successful, this project will enable a novel compact, coherent, tunable THz light source with power output suitable for technological applications (milliwatt level). In addition to broader wavelength flexibility, the THz nitride QCLs are expected to have superior performance in terms of operating temperature and efficiency at the longer wavelengths currently available to GaAs THz QCLs. The focus of this research project will be on THz lasers using lattice-matched nitrides, but the knowledge acquired will also be relevant to nitride optoelectronic devices operating in other spectral ranges such as the near-infrared (telecom) range. Moreover, the acquired knowledge will also be valuable for other types of devices, such as transistors, and to other material systems. This project will advance the understanding of MBE growth of lattice-matched III-Nitride materials for complex and thick device structures. Underlying processes of material growth on polar and non-polar GaN substrates will be studied in detail and compared. The goal is to achieve adequate understanding and control of the microstructure in order to realize the theoretical potential of the material system. The research program proposed here will also give opportunities for major contributions to the understanding of the physics of charge transport and optical transitions in nitride materials. Basic nitride band structure parameters, such as conduction band offsets and intrinsic polarization fields, will be established as a function of composition for the quaternary alloys. The fundamental and practical limitations of resonant tunneling in nitride heterostructures will be identified. Broader Impact: This project will enable a new class of compact, efficient terahertz power sources that will immediately impact a number of technological applications with broad benefits to society. The applications loosely fit into one of two main categories: THz spectroscopy, and THz imaging. THz spectroscopy is currently used in fields ranging from astronomy, and atmospheric science, to plasma fusion diagnostics and bio-chemical weapons detection. THz imaging has broad applications from airport security to medical imaging. This research program will provide unique interdisciplinary research opportunities to a diverse group of students at Purdue University. Special attention will be given to providing hands-on fabrication experience to under-represented undergraduate students. The excitement of scientific discovery will be conveyed through collaborations with several research groups in academia, industry (Kyma Technologies) and a federally funded laboratory (MIT Lincoln Laboratories). The PI's will be actively involved in mentoring minority students, in particular females, and students at risk. The research techniques and findings of this project will be integrated into graduate/undergraduate courses on the fundamentals of material growth by Molecular Beam Epitaxy and Optics, respectively. Outreach activities will include development of educational modules about basic optical properties of matter in the invisible ranges of the electromagnetic spectrum for public demonstrations in the Purdue's Physics on the Road Program. The PIs will also host activities for ScienceScape, a summer camp for middle-school girls. These activities will be focused on illustrating fundamental principles of light generation, propagation, and detection in a fun, project-oriented environment by asking students to create visually-compelling near- and far-infrared images.