Precision calibration of the silicon doping level in gallium arsenide epitaxial layers

An approach to precision calibration of the silicon doping level in gallium arsenide epitaxial layers is discussed that is based on studying the dependence of the carrier density in the test GaAs layer on the silicon- source temperature using the Hall-effect and CV profiling techniques. The parameters are measured by standard or certified measuring techniques and approved measuring instruments. It is demonstrated that the use of CV profiling for controlling the carrier density in the test GaAs layer at the thorough optimization of the measuring procedure ensures the highest accuracy and reliability of doping level calibration in the epitaxial layers with a relative error of no larger than 2.5%.     

Degradation-robust 850-nm vertical-cavity surface-emitting lasers for 25Gb/s optical data transmission

Highly efficient fast vertical-cavity surface-emitting lasers (VCSELs) for the 850-nm spectral range, promising for the development of optical interconnections with a data transmission rate of 25 Gbit/s per channel, are fabricated and studied. Lasers with a selectively oxidized current aperture 6 μm in diameter demonstrate multimode lasing with a quantum efficiency of 35–45% and a threshold current of 0.5–0.7 mA in the temperature range 20–85°C. According to the results of small-signal frequency analysis, the maximum modulation frequency of the lasers exceeds 17 GHz, with the rate of its increase with current exceeding 9 GHz/mA^1/2, which provides VCSEL operation at a rate of 25 Gbit/s in the entire working temperature range. Endurance tests for 3000 h did not reveal any sudden degradation of the lasers. The optical power at working point and the threshold current changed relative to that at the beginning of the tests by no more than 5 and 10%, respectively.     

Single-Lobe Single-Wavelength Lasing in Ultrabroad-Area Vertical-Cavity Surface-Emitting Lasers Based on the Integrated Filter Concept

We have studied broad-area vertical-cavity surface-emitting lasers grown in the antiwaveguiding approach (AVCSELs). The AVCSEL-type devices were fabricated in the ridge stripe geometry with openings in the top contact layer. Surface lasing was realized and evaluated for the devices with and without the integrated absorber section, acting as a selective filter for the emission modes propagating at finite tilt angle with respect to the normal to the surface (F-AVCSEL). It was found that the conventional AVCSEL device lases in high-order excited modes, tilted with respect to the normal to the surface, while lower order modes evolve at higher current densities causing a dramatic broadening of the emission spectrum. On the contrary, the F-AVCSEL emission is composed of a single spectral feature, which remains hardly affected up to the highest current densities >10 kA/cm². The far-field pattern is composed of a single zero-angle lobe with a beam divergence defined by the size of the opening in the top contact. No spectral features due to parasitic high-order modes were observed. The Gaussian-type single-wavelength surface-emitting lasing with an output power of 70 mW was realized in all-epitaxial wavelength-selective filter concept.     

Influence of optical losses on the dynamic characteristics of linear arrays of near-infrared vertical-cavity surface-emitting lasers

The effect of the level of internal and external optical losses on the dynamic characteristics of vertical-cavity surface-emitting lasers (VCSELs) in the spectral region of 850 nm is studied. It is shown that an increase in optical losses leads to a decrease in the speed of laser response and to the predominance of thermal effects, while a decrease in losses for the output of radiation brings about an increase in the response speed of the laser and the dominance of damping of the effective modulation frequency. Linear matrix emitters with the 1 × 4 format based on fast-response VCSEL with individual element addressing are produced and studied. Individual laser emitters with a current-aperture diameter of 5–7 μm provide lasing in the continuous-wave mode at room temperature in the region of 850 nm with threshold currents no higher than 0.5 mA, a differential efficiency no lower than 0.6 W/A, a modulation frequency as high as 20 GHz, and a MCEF factor of ～10 GHz/mA^1/2.     

Heterobarrier Varactors with Nonuniformly Doped Modulation Layers

Technical Physics Letters - Optimum shape of the capacitance–voltage (C–V) characteristic is a critical parameter determining the efficiency of frequency multiplication in heterobarrier...     

InAlAs/InGaAs/InP High-Electron-Mobility Transistors with a Composite Channel and Higher Breakdown Characteristics

Technical Physics Letters - A high-electron-mobility transistor (HEMT) based on InAlAs/InGaAs/InP heterostructures possessing higher breakdown characteristics is developed. An InGaAs composite...     

Molecular-beam epitaxy of InGaAs/InAlAs/AlAs structures for heterobarrier varactors

The molecular-beam epitaxy of InGaAs/InAlAs/AlAs structures for heterobarrier varactors is studied and optimized. The choice of the substrate-holder temperature, growth rate and III/V ratio in the synthesis of individual heterostructure regions, the thickness of AlAs inserts and barrier-layer quality are critical parameters to achieve the optimal characteristics of heterobarrier varactors. The proposed triple-barrier structures of heterobarrier varactors with thin InGaAs strained layers immediately adjacent to an InAlAs/AlAs/InAlAs heterobarrier, mismatched with respect to the InP lattice constant at an AlAs insert thickness of 2.5 nm, provides a leakage current density at the level of the best values for heterobarrier varactor structures with 12 barriers and an insert thickness of 3 nm.     

Emission-Line Width and α-Factor of 850-nm Single-Mode Vertical-Cavity Surface-Emitting Lasers Based on InGaAs/AlGaAs Quantum Wells

The emission-line width for 850-nm single-mode vertical-cavity surface-emitting lasers based on InGaAs/AlGaAs quantum wells is studied. The width of the emission line for a laser with a 2-μm oxide current aperture attains it minimum (~110 MHz) at an output power of 0.8 mW. As the optical output power is further increased, anomalous broadening of the emission line is observed; this is apparently caused by an increase in the α-factor as a result of a decrease in the differential gain in the active region under conditions of increased concentration of charge carriers and of high internal optical losses in the microcavity. The α-factor is estimated using two independent methods.     

Epitaxial InGaAs/InAlAs/AlAs Structures for Heterobarrier Varactors with Low Leakage Current

The quality of heteroboundaries and optimal conditions for epitaxial growth are critical parameters for obtaining low leakage currents of heterobarrier varactors in the InGaAs/InAlAs/AlAs material system. Grown by molecular-beam epitaxy, three-barrier heterobarrier varactor structures adjacent to InAlAs/AlAs/InAlAs barrier layers by additional mismatched InGaAs layers subjected to compressive stress show, under optimal epitaxy conditions, extremely low levels of leakage current density (not more than 0.06 A/cm² at a voltage of 5 V and 85°C) with relatively thin AlAs inserts (with a thickness of 2 nm).     

Determination of Inspection Parameters of Diesel Fuels

A method is developed for determining the inspection parameters of diesel fuels using gas chromatography. After one measurement which lasts on the order of 140 min, it is possible to determine the n–paraffin content, distillation curve, cetane number, density, and flash point of a sample. The proposed method can be used by any manufacturers, suppliers, refiners, and purchasers of crude oil cuts or petroleum products and control laboratories and research organizations.