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.     

Yellow–green organic light-emitting diode based on tris(2-methyl-8-quinolinolate) scandium

Efficient yellow–green electroluminescence emission at λ_max = 530 nm with CIE coordinates x = 0.3913, y = 0.4947 was obtained with organic light-emitting devices based on tris(2-methyl-8-quinolinolate) scandium (1). The device with the configuration of indium tin oxide/N,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine/1/Yb exhibits current efficiency of 3.1 cd/A and power efficiency of 1.8 lm/W at a luminance of 100 cd/m². The DFT calculations demonstrate that structural changes of the scandium complex 1 influence the electroluminescence spectrum, the better agreement with experimental data being achieved when monodentate ligands are taken into consideration.     

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.     

Lasing at 1.5 µm in quantum dot structures on GaAs substrates

Lasing at 1488–1515 nm in the temperature range 20–83°C was obtained in structures with an active region based on multiply stacked arrays of self-organized quantum dots grown on GaAs substrates. The threshold current density of a laser with four cleaved facets was 800 A/cm2 at room temperature. The method of wavelength extension is based on the use of a metamorphic buffer layer with an In content of about 20% intended for relieving the lattice mismatch stress.     

High efficiency (ηD>80%) long wavelength (λ>1.25 μm) quantum dot diode lasers on GaAs substrates

Diode lasers based on several layers of self-organized quantum dots (QD) on GaAs substrates were studied. The lasing wavelength lies in the range λ=1.25–1.29 μm, depending on the number of QD layers and optical losses. A record external differential efficiency of 88% and the characteristic temperature of threshold current, 145 K, were obtained. The internal losses, and also threshold and spectral characteristics, are correlated with the optical gain and radiative recombination efficiency, which are strongly dependent on the design of the active region and growth modes.     

High performance quantum dot lasers on GaAs substrates operating in 1.5 /spl mu/m range

Stacked InAs/InGaAs quantum dots are used as an active media of metamorphic InGaAs-InGaAlAs lasers grown on GaAs substrates by molecular beam epitaxy. High quantum efficiency (/spl eta//sub i/>60%) and low internal losses (/spl alpha/<3-4 cm/sup -1/) are realised. The transparency current density per single QD layer is estimated as /spl sim/70 A/cm/sup 2/ and the characteristic temperature is 60 K (20-85/spl deg/C). The emission wavelength exceeds 1.51 /spl mu/m at temperatures above 60/spl deg/C.     

Temperature characteristics of low-threshold high-efficiency quantum-dot lasers with the emission wavelength from 1.25 to 1.29 µm

The temperature behavior of the operation characteristics of low-threshold (the threshold current density is below 100 A/cm²) high-efficiency (differential quantum efficiency is as high as 88%) injection laser heterostructures is studied. The active region of structures emitting in the range from 1.25 to 1.29 μm included two, five, and ten layers of InAs-GaAs quantum dots. It is shown that both the threshold current density and the external differential quantum efficiency become N-shaped functions of temperature as the distribution of carriers in the active region changes from nonequilibrium to equilibrium one. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 37, No. 10, 2003, pp. 1270–1273. Original Russian Text Copyright ? 2003 by Novikov, Maksimov, Shernyakov, Gordeev, Kovsh, Zhukov, Mikhrin, Maleev, Vasil’ev, Ustinov, Alferov, Ledentsov, Bimberg.