Threshold Current Change Research Articles

MOCVD growth of high-performance InGaAsP/InGaP strain-compensated VCSELs with 850 nm emission wavelength

We present in this paper the metalorganic chemical vapor deposition growth and characterization of high-performance 850 nm InGaAsP/InGaP strain-compensated MQWs vertical-cavity surface-emitting lasers (VCSELs). The InGaAsP/InGaP MQWs growth condition was optimized using photoluminescence. These VCSELs exhibit superior characteristics, with threshold currents ∼0.4 mA, and slope efficiencies ∼0.6 mW/mA. The threshold current change is less than 0.2 mA and the slope efficiency drops by less than ∼30% when the substrate temperature is raised from room temperature to 85°C. These VCSELs also demonstrate high-speed modulation bandwidth up to 12.5 Gbit/s from 25°C to 85°C.

Analytical model for saturable aging in semiconductor lasers

We present an expression for the change in threshold current of a semiconductor laser diode as a function of the aging time under constant thermal and current aging. The expression forms a sigmoidal shape with the aging time, and is accurate in describing the increase of threshold current during aging. In the case where nonlinearities or “knees” occur in the threshold current aging curve, a multicomponent defect model is utilized to explain the observation. This multicomponent defect model allows multiple sigmoidal curves to be incorporated into the description. Each sigmoidal curve is thought to represent the growth of one type of defect complex. The parameters in the model are designed to have physical meaning that corresponds to the properties of the laser material. The model is compared to five popular models used to describe the threshold current aging characteristics.

Performance of 850 nm AlGaAs/GaAs implanted VCSELs utilizing silicon implantation induced disordering

In this paper, we report a novel implanted vertical surface emitting lasers (VCSELs) utilizing silicon implantation induced disordering. The VCSELs exhibit kink-free current–light output performance with threshold currents ∼2.4 mA, and the slope efficiencies ∼0.45 W/A. The threshold current change with temperature is minimal and the slope efficiency drops less than ∼30% when the substrate temperature is raised to 90 °C. The eye diagram of VCSEL operating at 2.125 Gb/s with 7 mA bias and 10 dB extinction ratio shows very clean eye with jitter less than 30 ps. We have accumulated life test data up to 5000 h at 100 °C/20 mA with exceptional reliability and the WHTOL (high temperature and high humidity 85 °C/85 operating lifetime) biased at 8 mA has passed over 2000 h.

Quantum Well Intermixing for Optoelectronic Applications

AbstractIon implantation induced intermixing of GaAs-AlGaAs quantum well structures with H, O and As ions is investigated by low temperature photoluminescence. Large energy shifts are observed in all the cases, though recovery of photoluminescence intensities in proton case is more significant than others. Energy shifts are linear with proton dose and no saturation was observed even up to a dose of ∼ 5 × 1016 cm−2. Saturation in energy shifts are seen for both As and 0 ions at high doses. Energy shifts are also found to be dependent on Al composition of the barriers. Wavelength shifted quantum well lasers are fabricated with energy shifts of about 5 nm with no changes in threshold current using proton implantation. Anodic oxide induced intermixing of GaAs-AlGaAs quantum wells is demonstrated.

Macroscopic Stress and Device Reliability of 1.3μm and 1.5μm Wavelength GaInAsP Channeled Substrate Buried Heterostructure Lasers

ABSTRACTThe macroscopic stress of 1.3μm and 1.5μm wavelength GaInAsP-InP channeled substrate buried heterostructure lasers is related with device reliability. The radius of curvature, R, of the device is taken as a measure of its macroscopic stress and the change in dc threshold current, ΔIth, after an accelerated aging test is taken as a measure of device reliability, with high ΔIth, indicating decreased reliability. R or ΔIth was changed by altering the p-side contact width or the p-side Au bonding pad thickness. No correlation was found between R and ΔIth. For example, changing the p-contact width from 6 to 125μm resulted in a reduction of ΔIth by a factor of 2 – 10 among the wafers studied. However, the change in the active layer stress, as determined by R−1, was at most only 25%. Similarly, increasing the Au bonding pad thickness from 0.6 to 9.0μm increased the active layer stress by a factor of 2, but with little change in Alt. It is concluded that the macroscopic stress does not affect device reliability for the GaInAsP lasers.

Effect of macroscopic stress on accelerated aging of GaInAsP channeled substrate buried heterostructure lasers

We report the results of the measurement of radius of curvature of 1.3 and 1.5 μm wavelength GaInAsP-InP channeled substrate buried heterostructure lasers. The objective of this investigation is to quantify the macroscopic stress present in the device and correlate it with device reliability. The change in dc threshold current (ΔIth) after an accelerated aging test was used as a measure to access device reliability, with high ΔIth indicating decreased reliability. Changes were made in the p-side metallization to bring about a change in either ΔIth or radius of curvature and they included two different contact widths and different thicknesses of the Au bonding pad. It is observed that no correlation between device curvature and ΔIth exists even though the modifications in the p metallization caused significant changes in both quantities. It is suggested that it is not the macroscopic device stress that is measured by the radius of curvature but localized stresses that may exist in the vicinity of the lasing active layer which would affect device reliability. It is surmised that the most important role of stress is its effect on the direction of defect migration with the principal driving force coming from the nonradiative electron-hole recombination occurring in the vicinity of the active layer.

Temperature Effects on Membrane Chloride Conductance and Electrical Excitability of Lizard Skeletal Muscle Fibres

ABSTRACT Intracellular recording techniques were used to study the effects of temperature on resting membrane conductances, electrical excitability and synaptic efficacy in fast-glycolytic (FG) skeletal muscle fibres from the lizard Dipsosaurus dorsalis. The conductance of the resting muscle membrane to chloride ions (gci) increased from 488 μS cm−2 at 15°C (pH7-8) to 730 μS cm−2 at 45°C (pH7·4), yielding a temperature coefficient (thermal ratio, Rio) of 1·14. Resting potassium conductance (gK) increased from 84μS cm−2 at 15 °C to 236 μS cm−2 at 45 °C (R10=1·41). Fibres bathed in Cl−-free Ringer’s solution were hyperexcitable, and produced repetitive action potentials both during and following intracellular current injection. At the preferred body temperature of Dipsosaurus (near 40°C) the fibres also fired repetitively in response to single nerve shock. The electrical excitability of Dipsosaurus fibres decreased with increasing temperature. Threshold current, measured at endplate regions of fibres bathed in normal Ringer’s solution, was 146 nA at 15°C and 353 nA at 45°C (R10= 1·34). Despite the temperature-dependent change in threshold current, at both 15 and 45 °C all fibres examined had suprathreshold neuromuscular transmission in response to single nerve shock. The relative thermal independence of gCl in Dipsosaurus fibres may be an adaptation that contributes to a large safety factor for neuromuscular transmission at the high body temperatures preferred by this lizard species.

Short-wavelength (≲6400 Å) room-temperature continuous operation of p-n In0.5(AlxGa1−x)0.5P quantum well lasers

Data are presented demonstrating short-wavelength (≲6400 Å) continuous (cw) laser operation of p-n diode In0.5(AlxGa1−x)0.5P multiple quantum well heterostructure (QWH) lasers grown lattice matched on GaAs substrates using metalorganic chemical vapor deposition. In the range from −30 °C to room temperature (RT≊300 K, λ≊6395 Å) the threshold current density changes from 2.3×103 A/cm2 (−30 °C) to 3.7×103 A/cm2 (RT, 300 K). The cw 300 K photopumped laser operation of the same quaternary QWH crystal is an order of magnitude lower in threshold (7×103 W/cm2, Jeq∼2.9×103 A/cm2) than previously reported for this crystal system, and agrees with the successful demonstration of cw 300 K laser diodes at this short wavelength.

GaAs/(GaAl)As deep Zn-diffused channeled-substrate laser

GaAs/(GaAl)As channeled-substrate laser with deep Zn diffusion for tight current confinement is reported. It has extremely low threshold current (as low as 12 mA), high differential quantum efficiency, single lateral and longitudinal mode operation up to 10 mW. It has T0 of about 200 °C and the rate of threshold current change is only about 0.07 mA/°C from 10 to 70 °C.