Population-inversion and gain estimates for a semiconductor TASER

We have investigated a solid-state design advanced (see Soref et al, in SPIE Proceedings, vol. 3795, p, 516, 1999) to achieve a terahertz-amplification-by-the-stimulated-emision-of-radiation (TASER), The original design was based on light-to heavy-hole intersubband transitions in SiGe/Si heterostructures, This work adapts the design to electron intersubband transitions in the more readily available GaAs/Ga1-xAlxAs material system. It is found that the electric-field induced anti-crossings of the states, derived from the first excited state with the ground states of a superlattice in the Stark-ladder regime, offers the possibility of a population inversion and gain at room temperature

Designing strain-balanced GaN/AlGaN quantum well structures: Application to intersubband devices at 1.3 and 1.55 mu m wavelengths

A criterion for strain balancing of wurtzite group-III nitride-based multilayer heterostructures is presented. Single and double strain-balanced GaN/AlGaN quantum well structures are considered with regard to their potential application in optoelectronic devices working at communication wavelengths. The results for realizable, strain-balanced structures are presented in the form of design diagrams that give both the intersubband transition energies and the dipole matrix elements in terms of the structural parameters. The optimal parameters for structures operating at lambda ~1.3 and 1.55 µm were extracted and a basic proposal is given for a three level intersubband laser system emitting at 1.55µm and depopulating via resonant longitudinal optical(LO)phonons (h omega(LO)approximate to 90 meV). © 2003 American Institute of Physics

Terahertz emission from silicon-germanium quantum cascades

Whilst most present day efforts towards the realisation of a silicon based laser are focused on the near-infrared (telecommunications) wavelengths, one of the most promising technical approaches is that of a silicon-germanium (SiGe) quantum cascade laser (QCL) operating in the far-infrared or terahertz frequency range. Until recently, the terahertz band (1--10 THz) has proved relatively inaccessible for science and engineering applications since it lies above the present upper frequency limit of millimetre wave electronic based oscillators, and below the range of near and mid-infrared solid state lasers and detectors. However, there is currently a great deal of interest in the development of terahertz technology for imaging and sensing applications: terahertz pulsed imaging has been shown to be capable of detecting caries (the precursor of decay) in human teeth 1, and there are also promising signs that the method could be used to detect basal cell carcinoma (a common form of skin cancer) 2. Many chemical and biological molecules have absorption lines in the THz band, and therefore applications are envisaged in chemical/biological detection and identification. THz imaging is also potentially suitable for baggage/personnel scanning for security applications, where it would provide a low-energy, non-ionising alternative to X-rays

Silicon based microphotonic: from basics to applications

The evolution of Si-based optoelectronics has been extremely fast in the last few years and it is predicted that this growth will still continue in the near future. The aim of the volume is to present different Si-based luminescing materials as porous silicon, rare-earth doped silicon, Si nanocrystals, silicides, Si-based multilayers and silicon-germanium alloy or superlattice structures. Moreover, the different devices needed for an all-Si-based optoelectronics are treated, spanning from light sources to waveguides, from amplifiers and modulators to detectors. Both the very basic treatments as well as applications to real prototype devices and integration in an optical integrated circuit are presented. Many still unresolved problems are underlined: the problem of electrical transport in low-dimensional Si systems, the possibility of gain in Si-based systems, the low modulation speed od Si-based LEDs, etc. The book gives a fascinating picture of the state-of-the-art in Si microphotonics and a perspective on what one can expect in the near future. For these reasons, it might be useful not only to graduate students but also to all researchers involved in this field