Quantum-well Laser Structures Research Articles

Design, Theoretical, and Experimental Investigation of Tensile-Strained Germanium Quantum-Well Laser Structure

Strain and band gap engineered epitaxial germanium (ε-Ge) quantum-well (QW) laser structures were investigated on GaAs substrates theoretically and experimentally for the first time. In this design, we exploit the ability of an InGaAs layer to simultaneously provide tensile strain in Ge (0.7–1.96%) and sufficient optical and carrier confinement. The direct band-to-band gain, threshold current density (Jth), and loss mechanisms that dominate in the ε-Ge QW laser structure were calculated using first-principles-based 30-band k·p electronic structure theory, at injected carrier concentrations from 3 × 1018 to 9 × 1019 cm–3. The higher strain in the ε-Ge QW increases the gain at higher wavelengths; however, a decreasing thickness is required by higher strain due to critical layer thickness for avoiding strain relaxation. In addition, we predict that a Jth of 300 A/cm2 can be reduced to <10 A/cm2 by increasing strain from 0.2% to 1.96% in ε-Ge lasing media. The measured room-temperature photoluminescence spectroscopy demonstrated direct band gap optical emission, from the conduction band at the Γ-valley to heavy-hole (0.6609 eV) from 1.6% tensile-strained Ge/In0.24Ga0.76As heterostructure grown by molecular beam epitaxy, is in agreement with the value calculated using 30-band k·p theory. The detailed plan-view transmission electron microscopic (TEM) analysis of 0.7% and 1.2% tensile-strained ε-Ge/InGaAs structures exhibited well-controlled dislocations within each ε-Ge layer. The measured dislocation density is below 4 × 106 cm–2 for the 1.2% ε-Ge layer, which is an upper bound, suggesting the superior ε-Ge material quality. Structural analysis of the experimentally realistic 1.95% biaxially strained In0.28Ga0.72As/13 nm ε-Ge/In0.28Ga0.72As QW structure demonstrated a strained Ge/In0.28Ga0.72As heterointerface with minimal relaxation using X-ray and cross-sectional TEM analysis. Therefore, our monolithic integration of a strained Ge QW laser structure on GaAs and ultimately the transfer of the process to the Si substrate via an InGa(Al)As/III–V buffer architecture would provide a significant step toward photonic technology based on strained Ge on a Si platform.

Optical gain and threshold current density for mid-infrared GaSbBi/GaSb quantum-well laser structure

This work is focused on band structure engineering and optical proprieties of GaSbBi/GaSb type I quantum well mid-infrared laser structure on GaSb substrate. Wherefore, the band alignment is tailored and optoelectronic properties are investigated for the proposed structure based on GaSb1−xBix/GaSb hetero-interfaces in the range of alloy compositions between 0≤x≤0.14. The electron and holes effective masses are deduced from the expressions extracted from the k.p model. The laser structure is designed to function at 2.7 μm at room temperature (RT), the addition of bismuth into the GaSb active region improve a preferment optical gain and the threshold current density (Jth) including computation of radiative, non radiative and Auger recombination. For typical carrier injection 5×1018cm-3at 300 k peak gain value of the order of 2000 cm−1 are reached and a modal gain equal to 96 cm−1 can be attained. A Jth around1.2 kA/cm2 is expected through moderate optical losses.

On the Application of Strain-Compensating GaAsP Layers for the Growth of InGaAs/GaAs Quantum-Well Laser Heterostructures Emitting at Wavelengths above 1100 nm on Artificial Ge/Si Substrates

Stressed InGaAs/GaAs quantum-well laser structures are grown by gas-phase epitaxy from organometallic compounds on GaAs substrates and artificial Ge/Si substrates based on Si(001) with an epitaxial metamorphic Ge layer. To suppress the relaxation of elastic stresses during the growth of InGaAs quantum wells with a high fraction of In, strain-compensating GaAsP layers are applied. The structural and radiative properties of the samples grown on substrates of various types are compared. Stimulated radiation at wavelengths up to 1.24 μm at 300 K is obtained for structures grown on GaAs substrates and at wavelengths up to 1.1 μm at 77 K, for structures grown on Ge/Si substrates.

Применение компенсирующих слоев GaAsP для роста лазерных гетероструктур с квантовыми ямами InGaAs/GaAs, излучающих на длинах волн больше 1100 нм, на искусственных подложках Ge/Si

AbstractStressed InGaAs/GaAs quantum-well laser structures are grown by gas-phase epitaxy from organometallic compounds on GaAs substrates and artificial Ge/Si substrates based on Si(001) with an epitaxial metamorphic Ge layer. To suppress the relaxation of elastic stresses during the growth of InGaAs quantum wells with a high fraction of In, strain-compensating GaAsP layers are applied. The structural and radiative properties of the samples grown on substrates of various types are compared. Stimulated radiation at wavelengths up to 1.24 μm at 300 K is obtained for structures grown on GaAs substrates and at wavelengths up to 1.1 μm at 77 K, for structures grown on Ge/Si substrates.

Experimental characterization of true spontaneous emission rate of optically-pumped InGaAs/GaAs quantum-well laser structure

In this paper, an experimental approach to acquiring true spontaneous emission rate of optically-pumped InGaAs/GaAs quantum-well laser structure is described. This method is based on a single edge-emitting laser chip with simple sample processing. The photoluminescence spectra are measured at both facets of the edge-emitting device and transformed to the spontaneous emission rate following the theory described here. The unusual double peaks appearing in the spontaneous emission rate spectra are observed for the InGaAs/GaAs quantum-well structure. The result is analyzed in terms of Indium-rich island and Model-Solid theories. The proposed method is suitable for electrically-pumped quantum-well laser structures, as well.

Active Region Design and Gain Characteristics of InP-Based Dilute Bismide Type-II Quantum Wells for Mid-IR Lasers

The electronic and optical properties of InP-based InGaAs/GaAsSbBi type-II quantum well (QW) structures are investigated theoretically. The detailed analyses of the InGaAs/GaAsSbBi type-II QW laser structures were based on a 14-band $\text {k}\cdot \text {p}$ model. The theoretical results indicate that adding Bi into InGaAs/GaAsSb type-II active regions on InP allows wavelength extension, but with minimal impact to transition matrix element. Moreover, the gain characteristics of the active region of laser were studied as a function of the Bi composition. It is shown that these type-II QW structures are suitable for mid-infrared (2– $4~{\mu }\text{m}$ ) operation at room temperature.

Monolithic Fabrication of InGaAs/GaAs/AlGaAs Multiple Wavelength Quantum Well Laser Diodes via Impurity-Free Vacancy Disordering Quantum Well Intermixing

InGaAs/GaAs/AlGaAs multiple wavelength quantum well (QW) semiconductor laser diodes (LDs) have been fabricated by impurity-free vacancy disordering (IFVD) QW intermixing (QWI) method. The IFVD-QWI process was carried out by sputtering-depositing SiO2 mask layers on top of the complete InGaAs/GaAs/AlGaAs QW laser structure, emitting at 980 nm wavelength, and followed by a rapid thermal annealing at 880 °C for 60 s. The lasing wavelength of the devices fabricated from the intermixed wafer was blue-shifted with the increase of the mask layer thickness. The maximum emission wavelength blue shift of a processed as-cleaved laser reached 112 nm with the output-power more than 1000 mW. By using such an IFVD-QWI technique, multi-wavelength integrated LDs have also been successfully fabricated from a single chip.

Revealing the effects of nitrogen on threshold current density in GaNxAsyP1−x−y/GaP/AlzGa1−zP type I QW laser structures by hydrostatic pressure

We present a comprehensive theoretical analysis of threshold current in dilute nitride direct bandgap Ga(NAsP)/GaP/AlGaP quantum wells (QW) on silicon substrates using model calculations. The pressure dependence of band structure, radiative and non-radiative recombination rates, optical confinement factor, transparency- and threshold-carrier densities are calculated in a range of 0–1GPa at room temperature. The effect of aluminium incorporation into cladding-layer Gallium Phosphide (GaP) with the employed five-layer slab waveguide model is considered and we have shown that incorporation of Aluminium (Al) into cladding-layer GaP increases the photon confinement in well layer. It is found that incorporation of Nitrogen (N) into GaAsP reduces the non-radiative Auger recombination rates which brings an improvement in threshold current. The comparison of our calculated results with that of the experimental data indicates that the Auger effect involving CHCC process can be considered as the dominant non-radiative loss mechanism at 300K.

Theory of the Electronic and Optical Properties of Dilute Bismide Quantum Well Lasers

We present a theoretical study of the gain characteristics of GaBi $_{x}$ As $_{1-x}$ /(Al)GaAs dilute bismide quantum well (QW) lasers. After providing a brief overview of the current state of development of dilute bismide alloys for semiconductor laser applications, we introduce the theoretical model we have developed for the description of the electronic and optical properties of dilute bismide QWs. Using a theoretical approach based on a 12-band k $\cdot$ p Hamiltonian we then undertake a detailed analysis of the electronic and optical properties of a series of ideal and real GaBi $_{x}$ As $_{1-x}$ /(Al)GaAs QW laser structures as a function of Bi composition $x$ . We theoretically optimize the gain characteristics of an existing low $x$ device by varying the Al composition in the barrier layers, which governs a trade-off between the electronic and optical confinement. The theoretical results are compared to temperature-dependent spontaneous emission measurements at low $x$ , which reveals the presence of significant Bi-induced inhomogeneous broadening of the optical spectra. We also investigate the gain characteristics of GaBi $_{x}$ As $_{1-x}$ /(Al)GaAs QW lasers at higher values of $x$ , including a QW designed to emit at 1.55 $\mu$ m. Our theoretical results elucidate the impact of Bi incorporation on the electronic and optical properties of GaAs-based QW lasers, and reveal several general trends in the gain characteristics as a function of $x$ . Overall, our analysis confirms that dilute bismide alloys are a promising candidate material system for the development of highly efficient, uncooled GaAs-based QW lasers operating at telecommunication wavelengths.

Study of N ions implantation induced quantum well intermixing in GaInP/AlGaInP quantum well structures

N ions implantation induced quantum well intermixing in GaInP/AlGaInP triple quantum-well laser structures was firstly reported in this work. N ions were implanted with the energy of 40 keV and dose of 1e17 ions/cm2, and thereafter rapid thermal annealing process were performed at 750 °C from 40 s to 200 s to induce the intermixing. The photoluminescence wavelength blue-shifts were found increased with the increasing time and the largest blue-shift of 54.9 nm was obtained for 200 s annealing. Surface morphology results shows that the photoluminescence improvement in the annealing samples came from the restoration effect of the layer crystal and hetero-structure interfaces. X-ray photoelectron spectroscopy tests shows that the implanting N ions tend to form Ga–N bonding besides generating point defect to induce quantum well intermixing.

Extremely Low-Threshold Current Density InGaAs/AlGaAs Quantum-Well Lasers on Silicon

An InGaAs/AlGaAs quantum-well laser structure was grown on a silicon substrate by adopting a three-step grown thin (1.8 μm) and simple buffer layer. The whole structure was grown by metalorganic chemical vapor deposition. The material quality was characterized by transmission electron microscopy, photoluminescence spectra, and electrochemical capacitance–voltage profiler. It shows that the threading dislocation density and interface roughness are effectively reduced, and the active region's optical properties grown on a silicon substrate are comparable to that grown on a GaAs substrate. Broad stripe lasers have also been fabricated. The cavity length and stripe width are 1 mm and 15 μm, respectively. An extremely low-threshold current density of 313 A/cm 2 has been achieved under pulsed condition at room temperature. Meanwhile, the laser can operate under continuous wave condition at the temperature of 240 K. The above results make us more confident for realizing better performance of Si-based III–V semiconductor lasers by further improvement of the material growth method.

Femtosecond superradiant emission in AlGaInAs quantum-well semiconductor laser structures

Ultrashort superradiant pulse generation from a 1580 nm AlGaInAs multiple quantum-well (MQW) semiconductor structure has been experimentally demonstrated for the first time. Superradiance is confirmed by analyzing the evolution of the optical temporal waveforms and spectra. Superradiant trends and regimes are studied as a function of driving condition. An optical pulse train is obtained at 1580 nm wavelength, with pulse durations as short as 390 fs and pulse peak powers of 7.2 W.

Optical Properties of Manufactured III-Vs and II-VIs Short Wavelength Laser Structures

We focus on most commonly used epitaxial growth techniques of quantum wells (QWs) and study the single electron transitions within the QW laser structures made with II-VIs (e.g. CdSe/ZnSe) and III-Vs (e.g. GaN/AlN), considering only emission of longitudinal optical (LO) phonons. Two different approaches have been employed in order to describe the initial electron wavefunctions in the continuum energy spectrum: the width of the barrier region is a) small b) large, relative to the electron mean free path. For the LO phonons, we have used the bulk phonon approximation and the dielectric continuum (DC) model to study the lattice dynamics in the crystal. Our theoretical models show that the scattering times for II-VIs are very short comparing to the III-Vs semiconductor (except the V-III nitrides) laser structures and highlight that the size of the well is of special importance for the laser operation. Keywords: MBE, MOCVD, large energy gaps, capture velocity, optical phonons, LED

High-Performance Visible Semiconductor Lasers Operating at 630 nm

A tensile-strained InGaP quantum-well laser structure operating around 630 nm has been designed. The structure offers low threshold current and beam divergence (19° full-width at half-maximum (FWHM) or 34° at 1/e <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) simultaneously by incorporating a V-profile layer within the waveguide. Single-mode lasers (630 nm) were fabricated and tested. The threshold current for coated 1-mm-long and 3-m-wide ridge lasers is only 30 mA, and the slope efficiency is 1.04 W/A. This level of performance makes the lasers ideal for display applications.

Effect of normal and reversed polarizations on optical characteristics of ultraviolet-violet InGaN laser diodes

The optical characteristics of ultraviolet-violet InGaN laser diodes with different numbers of quantum wells under normal and reversed polarizations are numerically investigated. For the laser structures under normal polarization, the lowest threshold current is obtained when the number of quantum wells is two in the spectral range of 380–408 nm. For the laser structures under reversed polarization, the single quantum-well laser structure possesses the lowest threshold current. The simulation results suggest that the physical origin for these phenomena is caused by the sufficiently suppressed electron and hole leakage currents when the laser diode is under reversed polarization.

Room temperature spectroscopic characterization of mid-infrared GaInSb quantum-well laser structures

Three GaInSb/AlGaInSb type I multi-quantum-well (QW) laser structures grown on GaAs, with increasingly strained QWs, aimed at emitting at ∼4 µm, are analysed using our Fourier transform infrared surface photo-voltage spectroscopy technique. The measurements clearly yield a full set of transitions including not only the barrier bandgap, but also the QW ground state transition, from which the device operating wavelengths can be inferred, and up to five excited state QW transitions. The full set of measured transition energies are then compared closely with those predicted by an 8-band k ⋅ p model which gives a generally good agreement for the QW transitions, but an indication that the current literature values for the AlGaInSb bandgap seem to be in considerable error for the present alloy compositions.

Fourier transform infrared surface photovoltage spectroscopy for the investigation of mid‐infrared semiconductor lasers

AbstractA novel application of the surface photovoltage spectroscopy (SPS) technique, using a Fourier transform infrared (FTIR) interferometer, has been developed for the investigation of narrow‐gap mid‐infrared semiconductor quantum well (QW) laser structures. We demonstrate the FTIR‐SPS technique at room temperature for a GaInSb/AlGaInSb type I QW laser structure, grown on GaAs, emitting in the mid‐infrared at ∼4 μm, revealing an unambiguous detection of the ground and excited state transitions of the GaInSb QW, as well as the AlGaInSb barrier bandgap energy. As a further corroboration of the new technique, the FTIR‐SPS spectrum of a ∼1.5 μm communication laser structure has also been measured and shown to be in good agreement with conventional grating‐based electro‐modulated reflectance and SPS spectroscopic measurements on this sample. A detailed numerical analysis of the room temperature FTIR‐SPS results for the mid‐infrared semiconductor laser structure is also presented, including a comparison with theoretical predictions of the QW transition energies. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

150 mm InP-to-Silicon Direct Wafer Bonding for Silicon Photonic Integrated Circuits

A low-temperature direct wafer bonding process was developed to realize the high-quality transfer of the largest (150 mm in diameter) available InP-based epitaxial structure onto the pre-patterned silicon-on-insulator (SOI) substrate. Over 95% bonding yield and a void free bonding interface was obtained. A InGaAsP multiple quantum-well (MQW) diode laser structure is well preserved after bonding, as indicated by the high-resolution X-ray diffraction (XRD) rocking curve measurement. XRD omega scans of the bonded wafers over a 9x9 matrix revealed a small bowing of only 64.12 micron, showing that the III-V epitaxial surface is relatively flat with low-strain. The first InGaAsP-based MQW hybrid Si evanescent racetrack ring lasers have been realized, showing comparable performance as previously InAlGaAs ring lasers.

Optical Gain and Spontaneous Emission in GaAsSb–InGaAs Type-II “W” Laser Structures

The modal gain, modal loss and spontaneous emission of a GaAsSb-based type-II quantum-well (QW) laser structure emitting at 1.3 mum have been experimentally determined as a function of current injection and temperature. The system is able to provide a maximum of 900 cm-1 of material gain from the n = 1 transition despite an electron-hole overlap of 32%, however, the gain from the n = 2 transition becomes dominant before this value can be achieved. The presence of the n = 2 transition has a detrimental effect on device performance, limiting the usable gain from the first transition and increasing the total radiative recombination current. Energy level calculations show that reducing the hole QW to 4 nm would increase the separation of the n = 1 and n = 2 transition by a further 45 meV, reducing the limiting effect of the transition. Carrier distribution spectra show the carriers are in thermal equilibrium for the temperatures and injection currents studied. A low radiative efficiency for this structure is measured due to a very large nonradiative current. We believe a combination of different mechanisms contribute to the nonradiative current.

Influence of GaAsP Insertion Layers on Performance ofInGaAsP/InGaP/AlGaAs Quantum-Well Laser

We report on the use of very thin GaAsP insertion layers to improve theperformance of an InGaAsP/InGaP/AlGaAs single quantum-well laserstructure grown by metal organic chemical vapour deposition. Compared tothe non-insertion structure, the full width at half maximum ofphotoluminescence spectrum of the insertion structure measured at roomtemperature is decreased from 47 to 38 nm indicating sharperinterfaces. X-ray diffraction shows that the GaAsP insertion layersbetween AlGaAs and InGaP compensates for the compressive strain toimprove the total interface. The laser performance of the insertionstructure is significantly improved as compared with the counterpartwithout the insertion layers. The threshold current is decreased from560 to 450 mA while the slope efficiency is increased from 0.61 to0.7 W/A and the output power is increased from 370 to 940 mW. The slopeefficiency improved is very high for the devices without coated facets.The improved laser performance is attributed to the suppression ofindium carry-over due to the use of the GaAsP insertion layers.