Guest Editorial

Abstract

It is a great pleasure for me to introduce this Special Issue of IET Optoelectronics, which is focussed on semiconductor optical devices. Once a year, a Special Issue on this topic is published in association with the Semiconductor and Integrated OptoElectronics (SIOE) conference held in Cardiff, UK. In 2016 SIOE celebrated its 30th anniversary and as always, featured an exciting programme with a very high standard of technical talks, some of which feature as extended versions in this issue. Semiconductor optoelectronics is constantly evolving with the emphasis on integration continuing to grow as a key theme, in both materials and device functions, and this is largely to meet the demand of technological trends. The push for photonic integrated systems and ‘smart’ devices is setting the scene for research and such systems are predominately designed with energy efficiency in mind. In the context of this field, so called ‘green photonics’ has a great importance for society and naturally promotes high impact for research proposals, which is particularly beneficial given the competitive nature of funding. In this issue, we showcase some of the key papers featured at SIOE, giving you a flavour of the subject areas of the conference sessions, many of which relate to the trends identified above. On the topic of green photonics, there are two papers concerning the development of solar cells: Wang, Q. et al. make use of a detailed balance model to investigate enhancing the efficiency of intermediate band solar cells by introducing carrier losses and compare this with the effect of using alloying and biaxial strain. Cappelluti, F. et al. present research on open-circuit voltage recovery in quantum dot solar cells. A numerical study is used to investigate the effect of wetting layer states and doping on the photovoltage loss in InAs/GaAs solar cells.This includes quantum mechanical simulations to analyse how the reduction of the wetting layer by overgrowth can influence the quantum dot states. It is an exciting and busy time for researchers in the area of terahertz (THz) technology, this relatively untapped region of the electromagnetic spectrum promises a plethora of applications, in medicine, quality-control and detection of explosives, to name a few. Low-cost, energy efficient ways to emit THz radiation using semiconductor optical devices is fast becoming a realistic prospect for commercial applications and will surely be a ubiquitous technology in the near future. THz research featured prominently at the conference with two papers included in the Special Issue: firstly Gwaro, J. et al. report on the implementation of a cost-effective compact THz source, which features a monolithically integrated dual-wavelength distributed Bragg reflector (DBR) semiconductor laser diode, making use of photo-conductive antennas. Secondly, Wang, Y. et al. describe their research on THz photoconductive antennas using low-temperature grown III-V compounds which incorporated DBRs to enhance the THz peak signal. Characterisation of novel laser devices and materials always forms a large part of the SIOE conference, through both experimentation and modelling. Modulation and tuneability of lasers formed a key topic area, as well as mode-locking and dynamic behaviour. Dugzul, O. et al. investigated the effect of optical-injection-locking on modulation dynamics of tuneable laser diodes and a travelling wave approach, making use of an integrated VPI, and PICS3D commercial software was used to assess the dynamic response of a three-section InGaAsP/InP tuneable laser. Tawfieq, M. et al. discuss the concept of numerical simulations of a widely tuneable 4-section sample-grating laser, emitting at 976 nm, and present data on the accessible wavelength range, the threshold current behaviour and gain characteristics. Experimental results, from monolithic colliding-pulse mode-locked lasers, containing chirped double-quantum-well active regions are reported by Prziwarka T. and co-workers. They discuss factors such as gain current, absorber length/voltage, and compromises made to achieve short (picosecond) pulses with relatively low repetition frequencies. Finally, our invited paper by Kellehur, B. et al. theoretically investigates an experimental phenomenon observed between mutually coupled quantum dot lasers, which exhibit a greatly reduced modal linewidth when mutually phase-locked. I thank the authors who contributed fully expanded papers for the Special Issue and I would also like to thank the referees for their time spent reviewing manuscripts and forming constructive comments. Now I shall leave you to enjoy reading this selection of papers and hope to see you all at future SIOE conferences. Dr. Samuel Shutts is a Research Associate in the School of Physics and Astronomy at Cardiff University. He is involved with the design, fabrication and characterisation of semiconductor light emitting devices. His current research interests include quantum dot lasers structures grown on silicon substrates; InP/AlGaInP quantum dot lasers; dual-wavelength sources; distributed Bragg reflectors and distributed feedback lasers and THz emission via difference frequency generation.