Room-temperature Threshold Current Research Articles

Compact vertical emitting ring interband cascade lasers for isotope-resolved CO2 sensing

We present a compact vertically emitting ring interband cascade laser (ICL) with low power consumption and the possibility for seamless integration into various CO2 sensing applications. Our devices exhibit desirable performance characteristics in battery-driven handheld devices, including room temperature (20 °C) threshold currents as low as 15 mA, small footprints, and stable single-mode emission, suitable for rapid isotope-resolved CO2 detection. Through epi-down bonding with sub-micron accuracy, we achieved robust integration of substrate-emitting ring ICLs, ensuring reliability and scalability that would be required for mass production. We present comprehensive experimental results validating the efficacy of our approach, including spectral analysis and CO2 sensing capabilities with limits of detection of 24 and 13 ppmv utilizing the 12CO2 P(60) and 13CO2 R(10) transitions in the ν3 fundamental band, respectively. The demonstrated devices hold great promise for a wide range of industrial applications, including environmental monitoring, process control, and atmospheric research, where compact low-power sensors are essential.

In situ annealing enhancement of the optical properties and laser device performance of InAs quantum dots grown on Si substrates.

The addition of elevated temperature steps (annealing) during the growth of InAs/GaAs quantum dot (QD) structures on Si substrates results in significant improvements in their structural and optical properties and laser device performance. This is shown to result from an increased efficacy of the dislocation filter layers (DFLs); reducing the density of dislocations that arise at the Si/III-V interface which reach the active region. The addition of two annealing steps gives a greater than three reduction in the room temperature threshold current of a 1.3 μm emitting QD laser on Si. The active region of structures grown on Si have a room temperature residual tensile strain of 0.17%, consistent with cool down from the growth temperature and the different Si and GaAs thermal expansion coefficients. This strain limits the amount of III-V material that can be grown before relaxation occurs.

Effect of passivation layers on characteristics of AlGaInP ridge waveguide laser diodes

We investigate the effect of passivation structure on the optical mode distribution and characteristics of the edge emitting ridge waveguide AlGaInP–GaInP visible laser diodes (LDs). For conventional designs of single-layer Si3N4 or SiO2 passivation, the variation of lateral near-field confinement and the horizontal far-field (FF) divergence can be determined via the modification of dielectric layer thickness. Thin passivation layer suffers from high absorption at the metal interface while thick passivation layer suffers from poor heat dissipation in the ridge waveguide and high scattering loss, resulting in high threshold. We propose a novel design of three-pair Al2O3/Ta2O5 multilayer optical thin films as passivation on the ridge waveguide, which can improve the laser characteristics and the heat dissipation. The measured room-temperature threshold current (Ith) and characteristic temperature (T0) are 44.5 mA and 104.2 K

High-Speed Low-Noise InAs/InAlGaAs/InP 1.55-$\mu{\rm m}$ Quantum-Dot Lasers

We present the static and dynamic properties of InAs quantum-dot (QD) lasers emitting near 1.55 μm. The used laser material comprises four QD layers and exhibits a high modal gain of about 40 cm-1. The 340-μ.m-long lasers show a room temperature threshold current of 38 mA and a maximum output power of 16 mW. The small signal modulation response is highly damped and carrier transport limited with a moderate 3-dB bandwidth of 5 GHz. This is accompanied by a flat relative intensity noise spectrum at a low level of -150 dBc/Hz. Neverthe- less, the laser exhibits record large signal modulation capabilities for a 1.5-μ.m QD laser: 15 Gb/s with a 4-dB on/off ratio.

Electrically driven hybrid Si/III-V Fabry-Pérot lasers based on adiabatic mode transformers

We report the first demonstration of an electrically driven hybrid silicon/III-V laser based on adiabatic mode transformers. The hybrid structure is formed by two vertically superimposed waveguides separated by a 100-nm-thick SiO2 layer. The top waveguide, fabricated in an InP/InGaAsP-based heterostructure, serves to provide optical gain. The bottom Si-waveguides system, which supports all optical functions, is constituted by two tapered rib-waveguides (mode transformers), two distributed Bragg reflectors (DBRs) and a surface-grating coupler. The supermodes of this hybrid structure are controlled by an appropriate design of the tapers located at the edges of the gain region. In the middle part of the device almost all the field resides in the III-V waveguide so that the optical mode experiences maximal gain, while in regions near the III-V facets, mode transformers ensure an efficient transfer of the power flow towards Si-waveguides. The investigated device operates under quasi-continuous wave regime. The room temperature threshold current is 100 mA, the side-mode suppression ratio is as high as 20 dB, and the fiber-coupled output power is ~7 mW.

Direct and Polymer Bonding of III-V to Processed Silicon-On-Insulator for Hybrid Silicon Evanescent Lasers Fabrication

We report the use of both direct and polymer bonding for the fabrication of Silicon/III-V evanescent laser. III-V structure is transferred to processed silicon-on-insulator (SOI) substrate at low temperature with a yield over 98%. We demonstrated the advantage of using a thick oxide layer (>100 nm), allowed by the innovative design, for limiting the void formation at the bonding interface. Silicon/III-V evanescent laser have been realized. The investigated device operates under quasi-continuous wave regime. The room temperature threshold current is 100 mA, the side mode suppression ratio is as high as 20dB, and the fiber-coupled output power is ~7mW.

An analysis of 1.55μm InAs∕InP quantum dash lasers

Calculations show that electron states are not confined in the dashes in 1.55μm InAs∕InP quantum dash-in-a-well laser structures. The combination of strain and three-dimensional confinement reduces the calculated density of states (DOS) near the valence band maximum, with the conduction and valence DOS then almost equal close to the band edges. Calculations and photoabsorption measurements show strongly polarized spontaneous emission and gain spectra. Experimental analysis shows the room temperature threshold current is dominated by nonradiative current paths.

1310nm silicon evanescent laser

We report the first 1310 nm hybrid laser on a silicon substrate. This laser operates continuous wave (C.W.) up to 105 degrees C. The room temperature threshold current of this laser is 30 mA, and the maximum single sided fiber-coupled output power is 5.5 mW.

High-performance 1.3 µm InAs/GaAs quantum-dot lasers with low threshold current and negative characteristic temperature

A high-growth-temperature GaAs spacer layer (HGTSL) is shown to significantly improve the performance of 1.3 µm multilayer InAs/GaAs quantum-dot (QD) lasers. The HGTSL inhibits threading dislocation formation, resulting in enhanced electrical and optical characteristics and hence improved performance of QD lasers. To further reduce the threshold current density and improve the room-temperature characteristic temperature (T0), the high-reflection (HR) coating and p-type modulation doping have been incorporated with the HGTSL technique. A very low continuous-wave room-temperature threshold current of 1.5 mA and a threshold current density of 18.8 A cm−2 are achieved for a three-layer device with a 1 mm HR/HR cavity, while a very low threshold current density of 48 A cm−2 and a negative T0 are achieved in the p-doped lasers.

Continuous-wave operation of GaInAsSb-GaSb type-II ridge waveguide lasers emitting at 2.8 /spl mu/m

We have realized compressively strained GaInAsSb-GaSb type-II double quantum-well lasers with an emission wavelength of 2.8 mum. Using broad area devices, an internal absorption of 9.8 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and an internal quantum efficiency of 0.57 is determined. For the increase of the threshold current with temperature, a T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> of 44 K is obtained. Narrow ridge waveguide lasers show continuous-wave laser operation at temperatures up to 45 degC, with room-temperature (RT) threshold current of 37 mA. At RT, the maximum optical output power per facet of an uncoated 800times7 mum <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ridge waveguide laser exceeds 8 mW

Influence of Electrostatic Confinement on Optical Gain in GaInNAs Quantum-Well Lasers

There remains controversy surrounding the cause of the magnitude and temperature sensitivity of the threshold current density of 1.3-/spl mu/m GaInNAs quantum-well (QW) lasers, with several authors attributing the strong temperature sensitivity to hole leakage, due to the relatively low valence band offset in GaInNAs/ GaAs QW structures. We use a Poisson solver along with a ten-band k.p Hamiltonian to calculate self-consistently the influence of electrostatic confinement on the optical gain in such lasers. We find that the inclusion of such effects significantly reduces the hole leakage effect, with the electrostatic attraction of the electrons significantly increasing the binding of heavy holes in the QW region. We conclude by comparison with previous theoretical and experimental studies that the room temperature threshold current is generally dominated by monomolecular recombination, while the temperature sensitivity can be explained as predominantly due to Auger recombination.

MOCVD growth of highly strained 1.3 μm InGaAs:Sb/GaAs vertical cavity surface emitting laser

In 0.45Ga 0.55As:Sb/GaAs (1.3 μm) vertical cavity surface emitting lasers (VCSELs) were grown by metalorganic chemical vapor deposition (MOCVD). A In 0.45Ga 0.55As:Sb/GaAs quantum well (QW) exhibited an emission wavelength of 1.26 μm with narrow full-width at half-maximum (FWHM) of 35.9 meV. For the fabricated VCSEL with 5 μm diameter oxide-confined aperture, a room-temperature (RT) threshold current of 2.1 mA and an output power of 0.9 mW with 1.3 μm emission were obtained. The 3 dB modulation frequency was measured to be 7.6 GHz.

High-performance three-layer 1.3-/spl mu/m InAs-GaAs quantum-dot lasers with very low continuous-wave room-temperature threshold currents

The combination of high-growth-temperature GaAs spacer layers and high-reflectivity (HR)-coated facets has been utilized to obtain low threshold currents and threshold current densities for 1.3-μm multilayer InAs-GaAs quantum-dot lasers. A very low continuous-wave (CW) room-temperature threshold current of 1.5 mA and a threshold current density of 18.8 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> are achieved for a three-layer device with a 1-mm HR/HR cavity. For a 2-mm cavity, the CW threshold current density is as low as 17 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for an HR/HR device. An output power as high as 100 mW is obtained for a device with HR/cleaved facets.

Improving high-temperature performance in continuous-wave mode InGaAsN/GaAsN ridge waveguide lasers

Continuous-wave (CW) mode operation InGaAsN/GaAsN double-quantum-well lasers with a laser wavelength of 1.295 µm are demonstrated by metal-organic chemical vapour deposition (MOCVD). With the use of a high-bandgap GaAs0.9P0.1 into the active region before the growth of p-type layers, a room temperature (RT) threshold current of 99 mA and the characteristic temperature (T0) values of 155 K in a temperature range of 25–95 °C and 179 K in a temperature range of 25–85 °C are obtained from a 4 × 1000 µm2 ridge waveguide uncoated laser diode. The T0 value of the conventional structure without the high-bandgap GaAs0.9P0.1 is 118 K in a temperature range of 25–95 °C. High-temperature performance is improved and the results of numerical analysis suggest that it may be attributed to the reduced electronic leakage current.

Effect of the growth parameters on the structure and morphology of InAs/InGaAs/GaAs DWELL quantum dot structures

The paper reports a systematic analysis by cross-sectional transmission electron microscopy of the structural parameters of molecular beam epitaxy grown multilayer InAs/InGaAs/GaAs dot-in well quantum dot (QD) lasers with a view to improve aspects such as uniformity of QD size, high spatial density, improved confinement and to reduce or eliminate defects. Based on our standard structure, previously optimised by considering only PL efficiency, we have modified parameters such as well composition and thickness and shown that the previously observed photoluminescence degradation as these parameters are increased, is due to threading dislocations. The use of the modified high-temperature growth for the barrier is shown to be effective in suppressing this dislocation mechanism. Processed laser devices with these samples exhibit room temperature threshold currents ∼30 A cm −1, amongst the best reported in the literature. Finally, the use of reduced (35 nm) barrier thickness produces both vertically correlated QDs and quantum wells, with the resulting structure resembling a ‘dot within a dot’ structure.

Self-aligned, buried heterostructure AlInGaAs laser diodesby micro-selective-area epitaxy

We describe the growth and characteristics of AlInGaAs, self-aligned buried heterostructure quantum well lasers deposited by micro-selective-area growth. The lateral waveguide is defined by metalorganic vapor-phase epitaxy in narrow stripe openings; and the natural tendency to form smooth, no-growth {111} sidewall planes produces a low-loss, single-mode waveguide. By proper adjustment of the growth conditions after the waveguide formation, the waveguide may be buried in p-type InP. A buried heterostructure (BH) laser is there formed in a single growth step, eliminating the deterioration associated with air exposure and etch damage, especially for AlInGaAs active regions. The AlInGaAs BH lasers formed in this simple manner exhibit good performance characteristics, with room-temperature threshold current of 4mA.

Continuous-wave operation of 1.55-μm vertical-cavity surface-emitting laser with digital-alloy active region using submonolayer superlattices

For the first time, a digital-alloy active region (DAAR) consisting of submonolayer superlattices was used in a 1.55-/spl mu/m vertical-cavity surface-emitting laser. The device showed continuous-wave operation with a room-temperature threshold current (I/sub th/) of 1.2 mA, maximum output power (P/sub max/) of 0.26 mW, and a differential quantum efficiency (/spl eta//sub d/) of 21%. These results indicate that the DAAR is at least as efficient as the analog-alloy active region and provides much better control of alloy composition and strain.

CW InGaN multiple-quantum-well laser diodes on copper and diamond substrates by laser lift-off

Continuous-wave (cw) InGaN multiple-quantum-well laser diodes grown on sapphire substrates by metalorganic chemical vapor deposition were successfully transferred onto copper and diamond using excimer laser lift-off. Room-temperature cw threshold currents as low as 87 mA with threshold voltages of 5.8 V were obtained for laser diodes on diamond substrates. GaN-based laser structures transferred onto Cu substrates show a significantly reduced thermal resistance resulting in a more than 2× increase in cw output power of more than 100 mW. High-quality cleaved facet have been obtained for free-standing GaN laser membranes after sapphire substrate removal.

CW InGaN Multiple-Quantum-Well Laser Diodes on Copper Substrates

Continuous-wave (cw) InGaN multiple-quantum-well laser diodes grown on sapphire substrates by metalorganic chemical vapor deposition (MOCVD) were successfully transferred onto copper using an excimer laser lift-off technique. For the laser diodes on copper substrates improved device performance was observed with room-temperature cw threshold currents as low as 68 mA and threshold voltages of 5.9 V. Differential quantum efficiencies of 0.7 W/A were obtained with a laser emission wavelength near 400 nm. GaN-based laser structures transferred onto copper substrates show a significantly reduced thermal resistance resulting in a more than twofold increase in cw output power to more than 100 W. High quality cleaved facets have been obtained for freestanding GaN laser membranes after sapphire substrate removal.

CW InGaN Multiple-Quantum-Well Laser Diodes on Copper Substrates

Continuous-wave (cw) InGaN multiple-quantum-well laser diodes grown on sapphire substrates by metalorganic chemical vapor deposition (MOCVD) were successfully transferred onto copper using an excimer laser lift-off technique. For the laser diodes on copper substrates improved device performance was observed with room-temperature cw threshold currents as low as 68 mA and threshold voltages of 5.9 V. Differential quantum efficiencies of 0.7 W/A were obtained with a laser emission wavelength near 400 nm. GaN-based laser structures transferred onto copper substrates show a significantly reduced thermal resistance resulting in a more than twofold increase in cw output power to more than 100 W. High quality cleaved facets have been obtained for freestanding GaN laser membranes after sapphire substrate removal.