P. Murzyn

Band anticrossing in dilute InNxSb1-x

Dilute nitrogen alloys of InSb exhibit extremely strong band gap bowing with nitrogen composition that has been associated with anticrossing between the localized resonant states of the nitrogen within the conduction band and the extended states of the conduction band itself. This also results in the conduction band dispersion having an enhanced nonparabolicity. We have measured the electron effective mass near the anticrossing by cyclotron resonance in InNxSb1−x alloys with absorption edge near 15 μm, using pulsed fields up to 150 T. The results directly demonstrate the band anticrossing and quantitatively confirm the increase of effective mass versus x predicted for InNxSb1−x by a tight binding calculation for low nitrogen concentration (x<0.01).

Picosecond intersubband dynamics in p-Si/SiGe quantum-well emitter structures

We report time-resolved (ps) studies of the dynamics of intersubband transitions in p-Si/SiGe multiquantum-well structures in the far-infrared (FIR) regime, ℏω<ℏωLO, utilizing the Dutch free electron laser, (entitled FELIX—free electron laser for infrared radiation). The calculated scattering rates for optic and acoustic phonon, and alloy scattering have been included in a rate equation model of the transient FIR intersubband absorption, and show excellent agreement with our degenerate pump-probe spectroscopy measurements where, after an initial rise time determined by the resolution of our measurement, we determine a decay time of ∼10 ps. This is found to be approximately constant in the temperature range from 4 to 100 K, in good agreement with the predictions of alloy scattering in the Si0.7Ge0.3 wells.

Si-based electroluminescence at THz frequencies

Experimental results of electroluminescence in the terahertz gap, at 6 THz (or 40 μm) from Si/SiGe multi quantum well structures, grown by a commercial chemical vapour deposition system are presented. Theoretical simulations were used to design the heterolayer structure and to explain the emission and absorption features. Electrical and materials characterisation is also presented to demonstrate the quality of the heterolayers.

Si/SiGe quantum-cascade emitters for terahertz applications

The quantum cascade laser provides one possible method of realizing high efficiency light emission from indirect band gap materials such as silicon. Strain-symmetrized Si/SiGe samples designed to investigate the intersubband properties of quantum wells are examined. Electroluminescence data from Si/SiGe quantum-cascade staircases demonstrating edge emission from heavy-hole to heavy-hole transitions and light-hole to heavy-hole transitions are presented. In surface-normal emission only light-hole to heavy-hole electroluminescence is observed at ( wavelength) as predicted by theory. Modulation-doped SiGe quantum well samples are also investigated to determine the underlying physics in the system. Results of picosecond time resolved studies of the dynamics of the intersubband transitions using a free electron laser are presented which show approximately constant relaxation times of below .

THz intersubband dynamics in p-Si/SiGe quantum well structures

We report time-resolved (ps) studies of the dynamics of intersubband transitions in p-Si/SiGe multi-quantum well structures in the FIR regime, ℏω<ℏωLO, utilizing the Dutch free electron laser, FELIX. The calculated scattering rates have been included in a rate equation model of the transient FIR intersubband absorption, and show excellent agreement with our degenerate pump–probe spectroscopy measurements where after an initial rise time determined by the resolution of our measurement we determine a decay time of . This is found to be approximately constant in the temperature range from 4 to , in good agreement with the predictions of alloy scattering in the Si0.7Ge0.3 wells.

Electroluminescence from Si/SiGe quantum cascade emitters

Abstract Intersubband electroluminescence results are presented from Si/SiGe quantum cascade emitters at 3.2 THz and at temperatures up to 150 K . The effect of adding doping into the active quantum wells was studied in addition to reduced barrier widths from previous measurements. While the current through the sample is increased by the addition of doping, the emitted power is reduced through additional free carrier absorption and Coulombic scattering. Free electron laser measurements confirm the intersubband transitions in the quantum wells of the cascade devices and produce non-radiative lifetimes of ∼20 ps between 4 and 150 K .

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 quantum cascade lasers for THz sources

This paper covers some recent advances in the search for a silicon quantum cascade laser. These include intersubband lifetime measurements, growth of high quality structures on buried suicide layers, and demonstration of THz electroluminescence.

LO phonon scattering as a depopulation mechanism in Si/SiGe quantum cascades

The linear optical phonon as a fast depopulation mechanism in Si/SiGe quantum cascade devices. Confirmed by pump-probe, the lifetime measurement is limited by the optical cycle of the source (<2 ps). Fourier transform spectroscopy shows intersubband electroluminescence with good agreement to theory.

Towards SiGe Terahertz VCSELs

Asymmetric rolling, in which the circumferential velocities of the upper and lower rolls are different, can give rise to intense plastic shear strains and in turn shear deformation textures through the sheet thickness. The ideal shear deformation texture of fcc metals can be approximated by the <111> // ND and {001}<110> orientations, among which the former improves the deep drawability. The ideal shear deformation texture for bcc metals can be approximated by the Goss {110}<001> and {112}<111> orientations, among which the former improves the magnetic permeability along the <100> directions and is the prime orientation in grain oriented silicon steels. The intense shear strains can result in the grain refinement and hence improve echanical properties. Steel sheets, especially ferritic stainless steel sheets, and luminum alloy sheets may exhibit an undesirable surface roughening known as ridging or roping, when elongated along RD and TD, respectively. The ridging or roping is caused by differently oriented colonies, which are resulted from the <100> oriented columnar structure in ingots or billets, especially for ferritic stainless steels, that is not easily destroyed by the conventional rolling. The breakdown of columnar structure and the grain refinement can be achieved by asymmetric rolling, resulting in a decrease in the ridging problem.