Mid-infrared Optoelectronics

Materials, Devices, and Applications

Eric Tournié,Laurent Cerutti

• Publisher: Woodhead Publishing
• Year: 2019
• ISBN:
  9780081027387
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Mid-infrared Optoelectronics: Materials, Devices, and Applications addresses the new materials, devices and applications that have emerged over the last decade, along with exciting areas of research. Sections cover fundamentals, light sources, photodetectors, new approaches, and the application of mid-IR devices, with sections discussing LEDs, laser diodes, and quantum cascade lasers, mid-infrared optoelectronics, emerging research areas, dilute bismide and nitride alloys, Group-IV materials, gallium nitride heterostructures, and new nonlinear materials. Finally, the most relevant applications of mid-infrared devices are reviewed in industry, gas sensing, spectroscopy, and imaging.

This book presents a key reference for materials scientists, engineers and professionals working in R&D in the area of semiconductors and optoelectronics.

• Provides a comprehensive overview of mid-infrared photodetectors and light sources and the latest materials and devices
• Reviews emerging areas of research in the field of mid-infrared optoelectronics, including new materials, such as wide bandgap materials, chalcogenides and new approaches, like heterogeneous integration
• Includes information on the most relevant applications in industry, like gas sensing, spectroscopy and imaging

Part One

Fundamentals

1

The physics of mid-infrared semiconductor materials and heterostructures

Stephen J. Sweeney; Timothy D. Eales; Igor P. Marko Department of Physics and Advanced Technology Institute, University of Surrey, Guildford, United Kingdom

Abstract

This chapter reviews the fundamental physics and associated limitations of semiconductor lasers operating across the mid-infrared (MIR) range of 2–20 μm. Using a combination of temperature and hydrostatic pressure dependence techniques, we have shown how short-wavelength 1.9–3.7-μm type I quantum well interband devices are dominated by Auger recombination, the nature and type of which depends upon the wavelength. In the intermediate wavelength range (3–7 μm), interband type II “W” lasers offer significant performance improvements despite the reduced wavefunction overlap. Quantum cascade lasers dominate at the longest MIR wavelengths with performance limited by intervalley scattering and leakage processes.

Keywords

Mid-infrared; Quantum well lasers; Interband cascade lasers; Quantum cascade lasers; Type I; Type II; Auger recombination; Temperature; Hydrostatic pressure; Strain; Carrier recombination; Efficiency; Carrier leakage

Acknowledgments

The authors gratefully acknowledge colleagues at the University of Surrey past and present for their contributions to this area of research, most notably Prof. Alf Adams, FRS who established the group at Surrey. The authors are very grateful to EPSRC (United Kingdom) for funding the majority of the work discussed in this chapter. We are also pleased to acknowledge the many international collaborators with whom we have worked over the years on the development of MIR lasers. Finally, we wish to dedicate this chapter to the memory of Prof. Dr. Markus-Christian Amann, a visionary in the field of semiconductor photonics and with whom the authors enjoyed many fruitful and enjoyable collaborations.

1.1 Introduction

Spanning the wavelength range between approximately 2 and 20 μm (500–5000 cm^{− 1}), the mid-infrared (MIR) is densely populated by important spectral features [1]. These include strong molecular absorption lines associated with the fundamental rotovibrational modes of many chemical functional groups that are vital for industrial and medical applications [2–11]. MIR also contains several atmospheric transmission windows. These regions of relatively high transparency are well positioned for atmospheric monitoring and have also attracted interest for free-space communications, security, and defense [12–15]. Another emerging application is in optical fiber networks. With growing demand on the optical fiber infrastructure, there is increasing pressure to expand the communication wavelengths into the MIR through photonic crystal fibers [16–18]. Despite the wealth of opportunities, MIR optoelectronics remains relatively immature compared to the near-infrared devices serving the telecommunications industry.

MIR lasers are a key component for these applications. There are three main semiconductor laser technologies employing quantum wells (QWs) within the active region: interband lasers, interband cascade lasers (ICLs), and quantum cascade lasers (QCLs) [19]. Their performance can be characterized by a number of metrics, including threshold current density, characteristic temperature, wall-plug efficiency, and peak output power, as will be discussed in this chapter [20]. To illustrate the domain of these technologies, examples of threshold current densities for lasers across the MIR are presented in Fig. 1.1. Note that while the threshold current density is an important measure of performance for semiconductor lasers, it is less useful for comparing interband and QCLs owing to the significantly different operating voltages required in each case, as discussed later in this chapter.

Fig. 1.1 Threshold current densities of type I diode lasers [21–32], type I ICLs [33–36], type II ICLs [37–41], and QCLs [42–70], measured at room temperature (around 290–300 K) in the MIR spectral range. Note that some additional variation will be introduced due to different device geometries, operational duty cycle, facet coatings, etc. Solid lines are a guide to the eye.

Extending the wavelength of conventional semiconductor lasers into the MIR is accompanied by several challenges. Some are inherently related to the narrow bandgap required for MIR interband transitions. Others are more prosaic but no less important, involving material limitations in heterostructure design and growth [71]. Intrinsic fundamental challenges include Auger recombination and free carrier absorption, which are known to scale rapidly with wavelength [72]. These challenges have not, however, prevented the development of interband lasers extending deep into the MIR. Bandgap narrowing is also accompanied by some advantages, such as a reduction in conduction band effective mass and, for compressively strained layers, a corresponding reduction of in-plane effective mass of the heavy hole band [73]. The reduced density of states lowers the carrier de...