InGaAsP Multi-quantum Wells Research Articles

III–V/Si Hybrid Laser Array with DBR on Si Waveguide**Supported by the National Basic Research Program of China under Grant No 2013CB632105, the National High Technology Research and Development Program of China under Grant No 2012AA012203, and the National Natural Science Foundation of China under Grant Nos 61404003 and 11174018.

We report an eight-channel silicon evanescent laser array operating at continuous wave under room temperature conditions using the selective-area metal bonding technique. The laser array is realized by evanescently coupling the optical gain of InGaAsP multi-quantum wells to the silicon waveguides of varying widths and patterned with distributed Bragg reflector gratings. The lasers have emission peak wavelengths in a range of 1537–1543 nm with a wavelength spacing of about 1.0 nm. The thermal impedances ZT of these hybrid lasers are evidently lower than those DFB counterparts

III-V/Si Hybrid Laser Array with Dbr on Si Waveguide

We report an eight-channel silicon evanescent laser array operating at continuous wave and room temperature conditions using selective-area metal bonding technique. The laser array is realized by evanescently coupling the optical gain of InGaAsP multi-quantum wells to the silicon waveguides of varying widths and patterned with distributed Bragg reflector (DBR) gratings. The lasers have emission peak wavelengths in range of 1537 and 1543 nm with a wavelength spacing of about 1.0 nm. The thermal impedance ZT of these hybrid lasers are evidently lower than those DFB counterparts.

Experimental evidence of hot carriers solar cell operation in multi-quantum wells heterostructures

We investigated a semiconductor heterostructure based on InGaAsP multi quantum wells (QWs) using optical characterizations and demonstrate its potential to work as a hot carrier cell absorber. By analyzing photoluminescence spectra, the quasi Fermi level splitting Δμ and the carrier temperature are quantitatively measured as a function of the excitation power. Moreover, both thermodynamics values are measured at the QWs and the barrier emission energy. High values of Δμ are found for both transition, and high carrier temperature values in the QWs. Remarkably, the quasi Fermi level splitting measured at the barrier energy exceeds the absorption threshold of the QWs. This indicates a working condition beyond the classical Shockley-Queisser limit.

4-λ InGaAsP-Si distributed feedback evanescent lasers with varying silicon waveguide width

A four-wavelength silicon hybrid laser array operating at room temperature is realized by evanescently coupling the optical gain of InGaAsP multi-quantum wells to the silicon waveguides of varying widths and patterned with distributed feedback gratings based on selective-area metal bonding technology. The lasers have emission peaks between 1539.9 and 1546.1 nm with a wavelength spacing of about 2.0 nm. The single laser has a typical threshold current of 50 mA and side-mode suppression ratio of 20 dB. The silicon waveguides are fabricated simply by standard photolithography and holographic lithography which are CMOS compatible.

Quantum well intermixing of multiple quantum wells on InP by argon plasma bombardment and the sputtered-SiO2 film

A quantum well intermixing process combining inductively-coupled-plasma reactive ion etching (ICP-RIE) and SiO2 sputtering film was investigated for the InGaAsP and InGaAlAs multi-quantum wells (MQWs). Optimal distance is 300-nm-thick for InGaAsP and of 200-nm-thick for InGaAlAs. Between MQWs and the upper cladding by ICP-RIE and bombardment, covering the 300-nm-thick sputtered SiO2 using rapid thermal annealer (RTA) processing resulted in a band-gap blue-shift of 90 nm for InGaAsP and of 60 nm for InGaAlAs.

Bonding InGaAsP/ITO/Si Hybrid Laser With ITO as Cathode and Light-Coupling Material

A 1.5-μ.m InGaAsP/ITO/Si hybrid laser with indium tin oxide (ITO) as both a cathode and a light-coupling material is presented. The InGaAsP gain structure with a transparent ITO cathode is flip-chip bonded onto a patterned silicon-on-insulator wafer. The light generated in the InGaAsP multiquantum wells is coupled through the ITO cathode into the Si waveguide to form an InGaAsP/ITO/Si hybrid laser. The threshold current density of this hybrid laser is 20 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 210 K. Due to the advantages of post-bonding and simplicity of the fabrication process, such a hybrid laser may be a promising Si light source.

VARIATION OF MQW DESIGN PARAMETERS IN A GaAs/InP-BASED LW-VCSEL AND ITS EFFECTS ON THE SPECTRAL LINEWIDTH

This paper reports on the simulative and comparative study on the effects of multi quantum well (MQW) design parameters on the spectral linewidth of a wafer-bonded GaAs/InP -based, 1.5 μm long-wavelength vertical-cavity surface-emitting laser (LW-VCSEL). The device employs InGaAsP MQWs sandwiched between GaAs/AlGaAs and GaAs/AlAs distributed Bragg reflectors (DBR) and utilizes a bottom-emitting, air-post design for current confinement. Among the modeled LW-VCSEL devices, the best linewidth achieved was 41.29 MHz at a peak wavelength of 1.57 μm for 8 MQWs with well thicknesses of 5.5 nm each and barrier thicknesses of 8 nm; equivalent to the experimental device developed in the past. Comparison of linewidth values calculated using developed analytical equations that link the MQW parameters to the spectral linewidth versus the actual linewidth from fabricated devices yields error ratios of ~ 6% proving a robust approximation has been achieved.

Long-wavelength MQW Vertical-cavity Surface Emitting Laser: Effects of Lattice Temperature

The lattice temperature in a 1.5 μm wavelength InP-based vertical-cavity surface-emiting laser (VCSEL) was varied between 273 K until 353 K using an industrial-based numerical simulator and its effects on the characteristics of the device was analysed. The temperature fluctuation has a direct effect on the gain distribution, causes a peak wavelength shift and is the precursor for various dark current processes within the laser. The device employs InGaAsP multi-quantum wells (MQW) sandwiched between GaAs/AlGaAs and GaAs/AlAs distributed Bragg reflectors (DBRs). The thermal resistance used to model the electrical contacts causes an approximate 13 K temperature rise above the ambient temperature (300 K) at a bias of 3 V and a 50 % increase in the threshold current is observed with temperature increment. Various heat sources elements within the VCSEL device were also analysed upon increment of lattice temperature.

Integratable and High Speed Complex-Coupled MQW-DFB Lasers Fabricated on Semi-Insulating Substrates

A novel integratable and high speed InGaAsP multi-quantum well (MQW) complex-coupled distributed feedback (DFB) laser is successfully fabricated on a semi-insulating substrate. The fabricated ridge DFB laser exhibits a threshold current of 26 mA, a slope efficiency of 0.14 W.A−1 and a side mode suppression ratio of 40 dB together with a 3 dB bandwidth of more than 8 GHz. The device is suitable for 10 Gbit/s optical fiber communication.

Influence of Zn doping profiles on excitation dependence of photoluminescence intensity in InGaAsP heterostructures

It is known that the Zn doping profile in strained multi-quantum-well (MQW) InGaAsP lasers strongly affects the electro-optical characteristics of these devices and their temperature sensitivity. A systematic investigation of the excitation dependence of the active layer photoluminescence (PL) intensity from compressively strained InGaAsP MQW pin laser material with different Zn doping profiles is described. When the pn junction lies within the active region, the excitation dependence of the PL intensity is superlinear at low excitation and linear at higher excitation. As the Zn profile is set back from the heterointerface creating a displaced pn junction from the active region, the excitation dependence is superlinear and linear at 300 K but becomes linear for all excitation powers at 77 K. The implications of these observations are discussed.

Controlled intermixing in InGaAsP multiquantum wells by plasma immersion ion implantation of argon

In this paper, the diffusion enhanced intermixing effect in strained InGaAsP multiquantum wells due to plasma immersion ion implantation (PIII) of Ar + and post-implant annealing is presented. Firstly, we report that a 20 kV Ar + PIII at a fluency of 10 16 cm −2 together with a furnace anneal at 650°C resulted in an enhanced blue shift in the photoluminescence (PL) peak. It was also found that by varying the Ar + dose or the implantation energy, we could control the extent of the implantation induced intermixing. For a sample that had half of the surface shielded during implantation, a bandgap step was observed between the implanted and non-implanted regions. Our results indicate that one can use this technique for localised fine-tuning of the bandgap energy, thus demonstrating its potential as a processing step for the fabrication of integrated photonic devices.

InP-based 1.55 µm resonant cavity light-emitting diode with two epitaxial mirrors

We report on the fabrication and characterisation of a resonant cavity light-emitting diode (RCLED) operating at 1.55 µm. As compared to conventional LEDs such devices merit from a higher emission intensity with a more narrow linewidth and are therefore promising as light sources in fibre optical communication systems. The present design is based on an InGaAsP multi-quantum well structure and utilises two InGaAsP/InP epitaxial distributed Bragg reflectors (DBRs), one 50 periods high reflectivity bottom mirror and a top out-coupling mirror with lower reflectivity. This gives the advantage of top-emission combined with the possibility of achieving very narrow linewidth. The process is fully monolithic and full wafer scale compatible.

Very high compositional homogeneity of 1.55 μm strain-compensated InGaAsP MQW structures by MOVPE under N 2 atmosphere

In order to improve the compositional homogeneity in metalorganic vapor phase epitaxy (MOVPE), growth under N 2 used as carrier gas has been applied for the first time to strain-compensated InGaAsP multi-quantum-well (MQW) structures on InP. Various InGaAs(P) layers and MQW structures have been grown by low-pressure MOVPE in a horizontal reactor at total gas flows Q tot=3.0–7.6 slm with substrate rotation using standard precursors. By replacing H 2 by N 2 the lateral homogeneities of the gap wavelength, lattice mismatch and layer thickness were considerably improved. The role of the carrier gas is discussed. The standard deviation σ(λ) of the wavelength over 40 mm of a 50 mm wafer of strain-compensated λ=1.55 μm laser structures with 10 QWs was reduced from 6.5 nm (H 2) to 0.55 nm (N 2), which is a factor of about 10! This is one of the best homogeneity values reported so far for InGaAsP grown in any type of MOVPE reactor with any precursors. Details of the growth parameters and results are presented along with the characteristics of distributed feedback (DFB) lasers and laser arrays produced from these structures.

MOMBE growth of highly tensile-strained InGaAsP MQWs and their applications to 1.3-μm wavelength low threshold current lasers

We have studied metalorganic molecular beam epitaxy (MOMBE) of InGaAsP multi-quantum wells (MQWs) with 0.5-1.8% tensile-strained well layers. The MQW photoluminescence intensity depends significantly on the barrier layer strain to compensate well layer strain. Optimizing the strain compensation conditions, i.e., keeping the net strain less than 0.3%, makes it possible to grow high optical quality MQWs with 1.8%-strained, 10-well layers. A critical thickness-net strain (t c -e*) curve for the tensile-strained MQWs has been experimentally determined by analyzing more than 50 samples with various strains and total thicknesses. The t c -e* curve fairly agrees with the one calculated by the Matthews formula for more 0.5% net strain, but the t c values are much higher than the expected ones below that range. For 6-well MQW lasers, the threshold current densities, J th 's, decrease with increasing tensile strain; the minimum J th obtained is 0.6 kA/cm 2 at 1.3% strain.

Simulation and analysis of 1.55 μm double-fused vertical-cavity lasers

Using a comprehensive numerical model, we analyze the first long-wavelength (1.55 μm) vertical-cavity surface-emitting lasers operating continuous-wave at room temperature (up to 33 °C). These double-fused lasers employ strain-compensated InGaAsP multi-quantum wells sandwiched between GaAs/AlGaAs distributed Bragg reflectors that are fused on both sides of the InP spacer. The two-dimensional model includes drift and diffusion of electrons and holes, finite-element thermal analysis, calculation of the internal optical field at threshold, and k⋅p band structure computations. The simulation shows excellent agreement with a large variety of experimental characteristics. Internal laser parameters like optical losses and injection efficiency are obtained. The thermal conductivity of the multilayer mirror is found to be only one third of the value expected. Temperature dependent absorption and Auger recombination within the active region as well as lateral leakage currents are identified as dominating loss mechanisms. The analysis shows great potential for high-temperature operation of double-fused vertical-cavity lasers.

Low threshold and high uniformity for novel 1.3-/spl mu/m-strained InGaAsP MQW DC-PBH LDs fabricated by the all-selective MOVPE technique

1.3-μm-strained InGaAsP multiquantum-well (MQW) double-channel planar buried heterostructure laser diodes (DC-PBH-LDs) were fabricated by all-selective metalorganic vapor phase epitaxy (MOVPE). In the fabrication process, the strained MQW active layer and current-blocking structures were directly formed by selective MOVPE without a semiconductor etching process. A low-threshold current (I/sub th/=2.6 mA@25/spl deg/C for 200-μm-long 70%-90% facets) and excellent high-temperature operation (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> =84 K, 25/spl deg/C-60/spl deg/C and T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> =70 K, 25/spl deg/C-85/spl deg/C) were achieved. Furthermore, extremely uniform threshold current and slope efficiency were observed, The median time to failure for these LDs was estimated to be more than 100000 h under the 85/spl deg/C-5 mW aging condition.

Structural and optical properties of 1.3 μm wavelength tensile-strained InGaAsP multiquantum wells grown by metalorganic molecular beam epitaxy

Tensile strained 0.5%–1.8% InGaAsP multiquantum wells (MQWs) grown by metalorganic molecular beam epitaxy are comprehensively characterized by using transmission electron microscopy (TEM), x-ray, photoluminescence (PL), lifetime, photocurrent, and absorption measurements. Cross-sectional and plan-view TEM photos reveal that, irrespective of the strain values, the tensile strained well layers have flat surfaces in the growth direction and consist of fine parallelepipeds laterally. Optimizing the strain compensation conditions, i.e., keeping the net strain less than 0.3%, makes it possible to grow high optical quality MQWs with 1.8%-strained well layers. As the well strain increases from 0.5% to 1.45%, however, the PL intensities of the misfit-dislocation-free MQWs monotonically decrease and the minority carrier lifetime decreases from 1.4 to 0.9 nsec. The laser threshold current density decreased with increasing well strain in the 0.5%–1.3% range, decreased to 0.6 kA/cm2 at 1.3% and slightly increased in the 1.45%–1.8% range.

Growth and characterization of MQW structures

We report for the first time on the growth of high-quality tensile-strained InAlGaAs InGaAsP multi-quantum wells on InP as well as bulk InAlGaAsP and InAlGaAsP InGaAsP multi-quantum wells on InP by LP-MOVPE. These structures show very good X-ray rocking curves and photoluminescence spectra and can be an interesting alternative for commonly used InGaAsP InGaAsP and InAlGaAs InAlGaAs structures.

Low-threshold strained multi-quantum well lasers fabricated by selective metalorganic vapor phase epitaxy without a semiconductor etching process

Strained InGaAsP multi-quantum well (MQW) buried hetero- (BH) laser diodes (LDs) on a p-InP substrate were fabricated by selective metalorganic vapor phase epitaxy (MOVPE). In the laser fabrication process, both the strained MQW active layer and current blocking structure were directly formed by selective MOVPE without a semiconductor etching process. This novel laser fabrication process produces extremely uniform device characteristics that are essential to the deployment of optical subscriber systems. Furthermore, important device design parameters (e.g. the active stripe shape or the leakage current path configuration) are precisely controlled by only the epitaxial growth steps. This highly controllable laser fabrication method results in a very low-threshold current with excellent uniformity (Ith = 1.78 ± 0.19 mA) for 20 consecutive LDs (L = 200 μm with 70%–90% coatings).

Numerical analysis of 1.54 μm double-fused vertical-cavity lasers operating continuous-wave up to 33 °C

The first vertical-cavity surface-emitting laser diodes operating continuous-wave at room temperature at 1.54 μm emission wavelength are analyzed using a comprehensive numerical simulation procedure. These lasers employ strain-compensated InGaAsP multi-quantum wells sandwiched between GaAs/AlGaAs mirrors that are double-fused on the InP spacer layers at both sides. The model includes finite element electro-thermal simulation, transfer-matrix optical analysis, and k⋅p band structure calculations. Internal laser parameters are obtained by fitting experimental data at different heat sink temperatures. Intervalence band absorption is found to be the dominating loss mechanism that restricts cw operation.