High-power 2.3 /spl mu/m laser arrays emitting 10 W CW at room temperature

High-power 2.3 /spl mu/m In(Al)GaAsSb/GaSb type-I double quantum-well diode laser arrays have been fabricated and characterised. Linear laser arrays with 19 100 /spl mu/m-wide elements on a 1 cm-long bar generated 10 W in continuous-wave (CW) mode and 18.5 W in quasi-CW mode (30 /spl mu/s/300 Hz) at a heatsink temperature of 18/spl deg/C.     

Effect of p-doping profile on performance of strainedmulti-quantum-well InGaAsP-InP lasers

Leakage of electrons from the active region of InGaAsP-InP laser heterostructures with different profiles of acceptor doping was measured by a purely electrical technique together with the device threshold current. Comparison of the obtained results with modeling data and SIMS analysis shows that carrier leakage of electrons over the heterobarrier depends strongly on the profile of p-doping and level of injection. In the case of a structure with an undoped p-cladding/waveguide interface, the value of electron leakage current can reach 20% of the total pumping current at an injection current density of 10 kA/cm at 50°C. It is shown that carrier leakage in InGaAsP-InP multi-quantum-well lasers can be minimized and the device performance improved by utilizing a p-doped separate-confinement-heterostructure layer     

Laser micromachining of SrTiO3 single crystal

Laser micromachining of piezoelectric materials has many advantages over other etching techniques for the fabrication of ultrasound transducer linear arrays for medical imaging. It can achieve high aspect ratios and high etch rates without the use of complicated photolithography techniques. We have investigated a laser projection etch technique to make linear arrays in single crystal (0 0 1) SrTiO₃ substrates as a model of epitaxial piezoelectric thick film heterostructure. Feature sizes of 17.5 μm were obtained with depth to width aspect ratios of 4:1. The effect of laser fluence on etching was studied and it was found that straighter sidewalls and flatter trench floors were achieved as laser fluence increases. On the other hand, higher laser fluence caused increase in heat affected zone by post-pulse plasma and made the top surfaces rougher because of the accumulation of evaporated materials. Clean top surfaces of the features were achieved by deposition and subsequent lift off of a YBa₂Cu₃O₇ sacrificial layer. In addition, the phases of recast layers on the sidewalls were characterized by four-circle X-ray diffraction with 2-D area detector before and after removed with a wet chemical etch solution. It was found that the use of the wet etchant could remove the thin polycrystalline recast layers.     

Synthetic multielement standards used for instrumental neutron activation analysis as rock imitations

Complex (multielemental) standards representing microelement composition of standard rocks such as trap ST-1 (USSR), gabbrodiorite SGD-1 (USSR), albitized granite SG-1 (USSR), basalt BCR-1 (USA) and granodiorite GSP-1 (USA) have been synthesized. It has been shown that the concentration of each microelement in the synthetic standards can be given with a high precision. Comparative investigation has been carried out of the synthetic imitations and the above natural standard rocks. It has been found that the result of the instrumental neutron activation analysis using the synthetic standards is as good as in the case when natural standard rocks are used. The results obtained have been also used for substantiation of the versatility of the method used for standard preparation, i.e. a generalization has been made of a possibility of using this method for the preparation of synthetic standards representing the microelement composition of any natural rocks with various compositions and concentrations of microelements.     

Measurement of Semiconductor Laser Gain by the Segmented Contact Method Under Strong Current Spreading Conditions

A segmented contact method for the measurement of optical gain is developed for the case of strong current spreading. A simple model of current spreading in a ridge laser with a segmented contact is proposed and analyzed. We show that current spreading effects should be taken into account in lasers with low threshold current densities and high ldquoopeningrdquo voltages. When applied to interband cascade lasers, the method gives an internal optical loss of ~ 10-17 cm^-1 and a differential gain of ~ 2.9 cm/A at 80 K, which agrees well with previously reported Hakki-Paoli data. The limitations of the technique are discussed.     

Wide-Dynamic-Range CMOS Image Sensors—Comparative Performance Analysis

A large variety of solutions for widening the dynamic range (DR) of CMOS image sensors has been proposed throughout the years. We propose a set of criteria upon which an effective comparative analysis of the performance of wide-DR (WDR) sensors can be done. Sensors for WDR are divided into seven categories: 1) companding sensors; 2) multimode sensors; 3) clipping sensors; 4) frequency-based sensors; 5) time-to-saturation (time-to-first spike) sensors; 6) global-control-over-the-integration-time sensors; and 7) autonomous-control-over-the-integration-time sensors. The comparative analysis for each category is based upon the quantitative assessments of the following parameters: signal-to-noise ratio, DR extension, noise floor, minimal transistor count, and sensitivity. These parameters are assessed using consistent assumptions and definitions, which are common to all WDR sensor categories. The advantages and disadvantages of each category in the sense of power consumption and data rate are discussed qualitatively. The influence of technology advancements on the proposed set of criteria is discussed as well.     

Interband tunneling depopulation in type-II InAs/GaSb cascade laser heterostructure

An exact analytical representation has been obtained for electron eigenstates in the full isotropic 8-band Kane model and applied to calculate the depopulation rate of the lower lasing state in the active region of a type-II intersubband cascade laser. We show that interband tunneling rate takes its maximum value when the depopulated states belong to the upper of the coupled electron- and hole-like subbands in the “leaky window” of the broken-gap InAs/GaSb heterostructure.     

GaSb-Based Mid-Infrared Single Lateral Mode Lasers Fabricated by Selective Wet Etching Technique with an Etch Stop Layer

We have demonstrated a wet etching technique for fabrication of narrow ridge lasers. Precise control over etching depth and ridge width was realized by introducing an etch stop layer into a laser structure and by using two etchants with different selectivity. The 6-μm-wide ridge laser emitting at 2 μm generated continuous-wave power of 70 mW at 20°C. Single lateral mode operation was observed up to 400 mA, corresponding to 8 × I _th.