Dynamics of photoluminescence and recombination processes in Sb-containing laser nanostructures

The dynamics of interband photoluminescence has been studied at various temperatures and excitation levels in structures with quantum wells based on InGaAsSb alloys and barriers based on AlGaAsSb and AlInGaAsSb alloys. The lifetimes of optically injected charge carriers in quantum wells at various temperatures and levels of optical excitation have been experimentally determined. An increase in the recombination rate in structures with deeper InGaAsSb/AlGaAsSb quantum wells for electrons is attributed to manifestation of resonant Auger recombination. The Auger recombination brings about heating of electrons and holes in lower subbands of dimensional quantization. The temperature of charge carriers in the course of Auger recombination is estimated using the equation for balance of power with accumulation of nonequilibrium optical phonons taken into account. The studied structures were used to fabricate lasers of two types with lasing wavelength of approximately 3 μm; it is shown that the use of a quinary alloy as the material for the barrier leads to an improvement in the characteristics of the lasers.     

Wide dynamic range snapshot APS for ultra low-power applications

A novel wide dynamic range (WDR) snapshot active pixel sensor for ultra-low power applications is presented. The proposed imager allows capturing of fast moving objects in the field of view and provides WDR by applying adaptive exposure time to each pixel, according to the local illumination intensity level. Driven by low-power dissipation requirements, the proposed pixel is operated by dual low voltage supplies (1.2 and 1.8 V) and utilizes an advanced low-power sensor design methodology. A test chip of a 32*32 array has been implemented in a standard 0.35-/spl mu/m CMOS technology. A single pixel occupies 18*32 /spl mu/m area and is expected to dissipate 18.5 nW at video rate. System architecture and operation are discussed and simulation results are presented.     

On IP traceback

In this article we present the current state of the art in IP traceback. The rising threat of cyber attacks, especially DDoS, makes the IP traceback problem very relevant to today's Internet security. Each approach is evaluated in terms of its pros and cons. We also relate each approach to practical deployment issues on the existing Internet infrastructure. The functionality of each approach is discussed in detail and then evaluated. We conclude with a discussion on some legal implications of IP traceback.     

Investigation of SO2 oxidation in humid air stream by high current density pulsed electron beam

The results of theoretical and experimental investigation of SO₂ oxidation in humid air by high current density pulsed electron beam are presented in this work. It is shown that energy costs of oxidation can be significantly reduced up to value A = 0.3 eV/mol corresponding to chain ion-molecule mechanism of oxidation in clusters.     

Diode lasers emitting at 3 μm with 300 mW of continuous-wave output power

Type-I double-quantum-well GaSb-based diode lasers operating at 3 mum with room-temperature continuous-wave output power above 300 mW and peak power-conversion efficiency near 8 were designed and fabricated. Laser heterostructure comprised quinary AlGaInAsSb alloy as barrier and waveguide material. Use of quinary alloy resulted in adequate hole confinement. The waveguide thickness was chosen to maximise modal differential gain. Continuous-wave threshold current density about 100 A/cm² per quantum-well and slope efficiency of 100 mW/A were demonstrated at 17degC.     

In-pixel autoexposure CMOS APS

A CMOS active pixel sensor (APS) with in-pixel autoexposure and a wide dynamic-range linear output is described. The chip features a unique architecture enabling a customized number of additional bits per pixel per readout, with minimal effect on the sensor spatial or temporal resolution. By utilizing multiple readouts via real-time feedback, each pixel in the field of view can automatically set an independent exposure time, according to its illumination. A customized, large increase in the dynamic range can be achieved and a scene containing both bright and dark regions can be captured. A prototype of 64 /spl times/ 64 pixels has been fabricated using 1-poly 3-metal CMOS 0.5 /spl mu/m n-well process available through MOSIS. Power dissipation is 3.7 mW at V/sub DD/ = 5 V. The special functions have been verified experimentally, and an increase of 2 bits over the inherent dynamic range captured is shown.     

Role of p-doping profile and regrowth on the static characteristicsof 1.3-μm MQW InGaAsP-InP lasers: experiment and modeling

In this paper, we study both experimentally and theoretically how the change of the p-doping profile, particularly the p-i junction placement, affects the output characteristics of 1.3-μm InGaAsP-InP multiple-quantum-well (MQW) lasers. The relationship between the p-doping profile before and after regrowth is established, and the subsequent impact of changes in the p-i junction placement on the device output characteristics, is demonstrated. Device characteristics are simulated including carrier transport, capture of carriers into the quantum wells, the quantum mechanical calculation of the properties of the wells, and the solution for the optical mode and its population self-consistently as a function of diode bias. The simulations predict and the experiments confirm that an optimum p-i junction placement simultaneously maximizes external efficiency and minimizes threshold current. Tuning of the base epitaxial growth Zn profile allows one to fabricate MQW devices with a threshold current of approximately 80 A/cm ² per well for devices with nine QW's at room temperature or lasers with a characteristic temperature T₀=70 K within the temperature range of 20°C-80°C     

Charge carrier recombination mechanisms in Sb-containing quantum well laser structures

The dynamics of interband luminescence in structures with InGaAsSb-based quantum wells and barriers of different types was studied at different temperatures and excitation levels. The lifetime of optically injected charge carriers in quantum wells at different temperatures and optical excitation levels was determined. An increased recombination rate in structures with deep electron quantum wells was discovered; it is associated with the occurrence of resonance Auger recombination. It was concluded that the application of quinary solid solutions as barriers in laser structures for a 3—4 fum wavelength range is to be preferred.     

A Simple Methodology to Measure the Dynamic Flexural Strength of Brittle Materials

A simple methodology is proposed for measuring the dynamic flexural strength of brittle materials. The proposed technique is based on 1-point impact experimental setup with (unsupported) small beam specimens. All that is needed is a measurement of the prescribed velocity as a boundary condition and the fracture time for a failure criterion, both to be input in a numerical (FE) model to determine the flexural strength. The specimen was modeled numerically and observed to be essentially loaded in bending until its final inertial failure. The specimen’s geometry was optimized, noting that during the very first moments of the loading, the specimen length does not affect its overall response, so that it can be considered as infinite. The use of small beam specimens allow large scale testing of the flexural strength and comparison between static and dynamic loading configurations. Preliminary experiments are presented to illustrate the proposed approach.     

Near band edge optical absorption and photoluminescence dynamics in bulk InAsN dilute-nitride materials

Dilute-nitride InAs bulk materials with up to 2.25% of nitrogen were grown by molecular beam epitaxy on InAs substrates. Photoluminescence (PL) and optical absorption measurements demonstrate a bandgap reduction by up to 150 meV with increasing nitrogen incorporation. Close correspondence of the energies of the photoluminescence peak and absorption edges indicate limited Moss–Burstein shift. Minority carrier lifetimes in the nanosecond range are measured using an ultra-fast PL up-conversion technique for the samples with up to 2% of nitrogen. Orders of magnitude advance of the carrier relaxation lifetimes as compared to GaSbN encourage development of the InAsN as a potential material for mid-IR detector applications.