There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

The role of extended and point defects, and key impurities such as C, O, and H, on the electrical and optical properties of GaN is reviewed. Recent progress in the development of high reliability contacts, thermal processing, dry and wet etching techniques, implantation doping and isolation, and gate insulator technology is detailed. Finally, the performance of GaN-based electronic and photonic devices such as field effect transistors, UV detectors, laser diodes, and light-emitting diodes is covered, along with the influence of process-induced or grown-in defects and impurities on the device physics.

Gan : processing, defects, and devices

Over the past three decades a new spectroscopic technique with unique possibilities has emerged. Based on coherent and time-resolved detection of the electric field of ultrashort radiation bursts in the far-infrared, this technique has become known as terahertz time-domain spectroscopy (THz-TDS). In this review article the authors describe the technique in its various implementations for static and time-resolved spectroscopy, and illustrate the performance of the technique with recent examples from solid-state physics and physical chemistry as well as aqueous chemistry. Examples from other fields of research, where THz spectroscopic techniques have proven to be useful research tools, and the potential for industrial applications of THz spectroscopic and imaging techniques are discussed.

Terahertz spectroscopy and imaging – Modern techniques and applications

Recent research results pertaining to InN, GaN and AlN are reviewed, focusing on the different growth techniques of Group III-nitride crystals and epitaxial films, heterostructures and devices. The chemical and thermal stability of epitaxial nitride films is discussed in relation to the problems of deposition processes and the advantages for applications in high-power and high-temperature devices. The development of growth methods like metalorganic chemical vapour deposition and plasma-induced molecular beam epitaxy has resulted in remarkable improvements in the structural, optical and electrical properties. New developments in precursor chemistry, plasma-based nitrogen sources, substrates, the growth of nucleation layers and selective growth are covered. Deposition conditions and methods used to grow alloys for optical bandgap and lattice engineering are introduced. The review is concluded with a description of recent Group III-nitride semiconductor devices such as bright blue and white light-emitting diodes, the first blue-emitting laser, high-power transistors, and a discussion of further applications in surface acoustic wave devices and sensors.

https://iopscience.iop.org/article/10.1088/0022-3727/31/20/001/pdf

Growth and applications of Group III-nitrides

The lowest room-temperature threshold current density, 26 A/cm/sup 2/, of any semiconductor diode lasers is reported for a quantum dot device with a single InAs dot layer contained within a strained In/sub 0.15/Ga/sub 0.85/As quantum well. The lasers are epitaxially grown on a GaAs substrate, and the emission wavelength is 1.25 /spl mu/m.

Extremely low room-temperature threshold current density diode lasers using InAs dots in In0.15Ga0.85As quantum well

Amplified spontaneous emission measurements are investigated below threshold in InAs quantum-dot lasers emitting at 1.22 /spl mu/m. The dot layer of the laser was grown in a strained quantum well (QW) on a GaAs substrate. Ground state gain is determined from cavity mode Fabry-Perot modulation. As the injection current increases, the gain rises super-linearly while changes in the index of refraction decrease. Below the onset of gain saturation, the linewidth enhancement factor is as small as 0.1, which is significantly lower than that reported for QW lasers.

Gain and linewidth enhancement factor in InAs quantum-dot laser diodes

The optical characteristics of the first laser diodes fabricated from a single-InAs quantum-dot layer placed inside a strained InGaAs QW are described. The saturated modal gain for this novel laser active region is found to be 9-10 cm/sup -1/ in the ground state. Room temperature threshold current densities as low as 83 A/cm/sup 2/ for uncoated 1.24-/spl mu/m devices are measured, and operating wavelengths over a 190-nm span are demonstrated.

Optical characteristics of 1.24-μm InAs quantum-dot laser diodes

The first self-assembled InAs quantum dash lasers grown by molecular beam epitaxy on InP (001) substrates are reported. Pulsed room-temperature operation demonstrates wavelengths from 1.60 to 1.66 μm for one-, three-, and five-stack designs, a threshold current density as low as 410 A/cm2 for singlestack uncoated lasers, and a distinctly quantum-wire-like dependence of the threshold current on the laser cavity orientation. The maximal modal gains for lasing in the ground-state with the cavity perpendicular to the dash direction are determined to be 15 cm–1 for single-stack and 22 cm–1 for five-stack lasers.

Room-temperature operation of InAs quantum-dash lasers on InP [001]

The authors report an enhanced infrared spectral response of GaAs-based solar cells that incorporate type II GaSb quantum dots (QDs) formed using interfacial misfit array growth mode. The material and devices, grown by molecular beam epitaxy, are characterized by current-voltage and spectral response characteristics. From 0.9to1.36μm, these solar cells show significantly more infrared response compared to reference GaAs cells and previously reported InAs QD solar cells. The short circuit current density and open circuit voltages of solar cells with and without dots measured under identical conditions are 1.29mA∕cm2, 0.37V and 1.17mA∕cm2, 0.6V, respectively.

/pdf/gasb-gaas-type-ii-quantum-dot-solar-cells-for-enhanced-3la5flym7z.pdf

Luke F. Lester

Papers

Extremely low room-temperature threshold current density diode lasers using InAs dots in In0.15Ga0.85As quantum well

Gain and linewidth enhancement factor in InAs quantum-dot laser diodes

Optical characteristics of 1.24-μm InAs quantum-dot laser diodes

Room-temperature operation of InAs quantum-dash lasers on InP [001]

GaSb∕GaAs type II quantum dot solar cells for enhanced infrared spectral response