Highly mismatched semiconductor alloys such as GaNxAs1 − x and GaBixAs1 − x have several novel electronic properties, including a rapid reduction in energy gap with increasing x and also, for GaBiAs, a strong increase in spin-orbit-splitting energy with increasing Bi composition. We review here the electronic structure of such alloys and their consequences for ideal lasers. We then describe the substantial progress made in the demonstration of actual GaInNAs telecommunication (telecom) lasers. These have characteristics comparable to conventional InP-based devices. This includes a strong Auger contribution to the threshold current. We show, however, that the large spin-orbit-splitting energy in GaBiAs and GaBiNAs could lead to the suppression of the dominant Auger recombination loss mechanism, finally opening the route to efficient temperature-stable telecomm and longer wavelength lasers with significantly reduced power consumption.

Band engineering in dilute nitride and bismide semiconductor lasers

Highly mismatched semiconductor alloys such as GaNAs and GaBiAs have several novel electronic properties, including a rapid reduction in energy gap with increasing x and also, for GaBiAs, a strong increase in spin orbit- splitting energy with increasing Bi composition. We review here the electronic structure of such alloys and their consequences for ideal lasers. We then describe the substantial progress made in the demonstration of actual GaInNAs telecomm lasers. These have characteristics comparable to conventional InP-based devices. This includes a strong Auger contribution to the threshold current. We show, however, that the large spin-orbit-splitting energy in GaBiAs and GaBiNAs could lead to the suppression of the dominant Auger recombination loss mechanism, finally opening the route to efficient temperature-stable telecomm and longer wavelength lasers with significantly reduced power consumption.

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A review on the recent developments in the field of long-wavelength (A > 1.2 μm) high-brightness optically-pumped semiconductor disk lasers (OPSDLs) is presented. As thermal effects have such a crucial impact on the laser performance particular emphasis is given to modelling the thermal behaviour and optimisation of the heat-sinking. Selected OPSDL devices, realized in different III-V and IV-VI semiconductor material systems, with corresponding emission wavelengths between 1.2 μm and 5.3 μm are presented. Specific applications in this broad spectral range are addressed and methods to obtain high output power are discussed in terms of the underlying material properties and device operating principles.

High-brightness long-wavelength semiconductor disk lasers

The mid-infrared (mid-IR) is a wavelength range with a variety of technologically vital applications in molecular sensing, security and defense, energy conservation, and potentially in free-space communication. The recent development and rapid commercialization of new coherent mid-infrared sources have spurred significant interest in the development of mid-infrared optical systems for the above applications. However, optical systems designers still do not have the extensive optical infrastructure available to them that exists at shorter wavelengths (for instance, in the visible and near-IR/telecom wavelengths). Even in the field of optoelectronic sources, which has largely driven the growing interest in the mid-infrared, the inherent limitations of state-of-the-art sources and the gaps in spectral coverage offer opportunities for the development of new classes of lasers, light emitting diodes and emitters for a range of potential applications. In this topical review, we will first present an overview of the current state-of-the-art mid-IR sources, in particular thermal emitters, which have long been utilized, and the relatively new quantumand interband-cascade lasers, as well as the applications served by these sources. Subsequently, we will discuss potential midinfrared applications and wavelength ranges which are poorly served by the current stable of mid-IR sources, with an emphasis on understanding the fundamental limitations of the current source technology. The bulk of the manuscript will then explore both past and recent developments in midinfrared source technology, including narrow bandgap quantum well lasers, type-I and type-II quantum dot materials, type-II superlattices, highly mismatched alloys, lead-salts and transitionmetal-doped II-VI materials. We will discuss both the advantages and limitations of each of the above material systems, as well as the potential new applications which they might serve. All in all, this topical review does not aim to provide a survey of the current state of the art for mid-IR sources, but instead looks primarily to provide a picture of potential next-generation optical and optoelectronic materials systems for mid-IR light generation.

https://iopscience.iop.org/article/10.1088/2040-8986/aa939b/pdf

Next-generation mid-infrared sources

We review the recent developments in GaAs-based 1.55-mum lasers grown by molecular beam epitaxy (MBE). While materials growth is challenging, the growth window appears to be relatively broad and is described in detail. The key considerations for producing high-quality GalnNAsSb material emitting at 1.55-mum regime are examined, including the nitrogen plasma conditions, ion removal from the nitrogen flux, surfactant- mediated growth, the roles of various V-II ratios, the growth temperature, the active region thermal budget, proper annealing, and composition. We find that emission may be tuned throughout the 1.55-mum communications band without penalty to the optical quality varying only one parameter - the total growth rate. This powerful result is validated by the demonstration of low-threshold edge-emitting lasers throughout the 1.55-mum regime, including threshold current densities as low as 318 A/cm2 at 1.54 mum. Additional characterization by Z-parameter techniques, cavity length studies, and band offset measurements were performed to better understand the temperature stability of device performance. Lasing was extended as far as 1.63 mum under nonoptimized growth conditions. The GaAs-based dilute-nitrides are emerging as a very promising alternative to InP-based materials at 1.55-mum due to their high gain, greater range of achievable band offsets, as well as the availability of lattice-matched AlAs-GaAs materials and native oxide layers for vertical-cavity surface-emitting lasers (VCSELs). Indeed, this effort has enabled the first electrically injected C-band VCSEL on GaAs.

Recent Progress on 1.55- $\mu{\hbox {m}}$ Dilute-Nitride Lasers

Low threshold InGaAsN/GaAs lasers beyond 1500 nm

We compare the luminescence efficiency (i.e., room-temperature photoluminescence intensity), fluctuations in composition and thickness, degree of localization, and luminescence decay times of In0.37Ga0.63As0.983N0.017 quantum wells grown by molecular-beam epitaxy at different temperatures and annealed under a comprehensive variety of conditions. Luminescence efficiency is not directly coupled to structural nonuniformity or localization, and even three-dimensional growth is not detrimental by itself. In contrast, there is always a correlation between luminescence efficiency and nonradiative decay time. Therefore, the luminescence efficiency of InGaAsN quantum wells depends almost exclusively on the density of nonradiative recombination centers, while the influence of structural nonuniformity is negligible.

Influence of structural nonuniformity and nonradiative processes on the luminescence efficiency of InGaAsN quantum wells

In0.37Ga0.63As0.983N0.017 quantum wells grown by molecular beam epitaxy at different temperatures were annealed under a comprehensive variety of conditions either in Ar or in H2. A significantly higher luminescence efficiency (i.e., room temperature photoluminescence intensity) can be obtained for annealing in H2. Thus, there is an additional chemical effect beyond the mere thermal effect of annealing. At the same time, band gap and localization of charge carriers are not influenced. Hence, the electronic structure is not affected by the H2 treatment. Indirect experiments suggest that hydrogen is reversibly incorporated into the samples and can be removed by mild annealing in Ar.

Annealing of InGaAsN quantum wells in hydrogen

We present a systematic study on realising low-threshold, long-wavelength lasers based on simplemost InGaAsN/GaAs SWQ structures grown on GaAs by plasma-assisted MBE. Record-low threshold current densities up to 1430 nm are reported.

G. Jaschke

Papers

Low threshold InGaAsN/GaAs lasers beyond 1500 nm

Influence of structural nonuniformity and nonradiative processes on the luminescence efficiency of InGaAsN quantum wells

Annealing of InGaAsN quantum wells in hydrogen

Record-low thresholds of InGaAsN/GaAs SQWs lasers