Separate Confinement Heterostructure Research Articles

Effect of separate confinement hetero-structure layer on tunnel injection transistor laser-based transmitter for high-speed optical communication networks

Transistor Laser has already established as a promising candidate for high speed optical interconnects and optical telecommunication networks. The present work is focused on the performance of multiple quantum wells (MQW) based transistor laser by incorporating tunnel injection phenomenon and it’s performance by varying the width of the separate confinement heterostructure layer. The virtual state (VS) is assumed as a path for the movement of injected charge carriers from bulk to nanostructures. We have estimated the various characteristics such as base threshold current, light power output, and optical modulation response by considering various physical parameters such as diffusion time, gain compression factor, optical confinement factor, photon lifetime, tunneling time and diffusion length, as a function of separate confinement hetero-structure (SCH) layer thickness. It is found that with increasing thickness of the SCH layer, base threshold current reduces, the light output power increases, but the optical modulation response remains almost constant, which ensures the potentiality of the proposed structure for high speed opto-electronic transmitter with low power consumption.

MOVPE grown GaInAsP/GaInAsP SCH-MQW laser diode on directly-bonded InP/Si substrate

We have successfully obtained a metalorganic vapor phase epitaxy (MOVPE) grown GaInAsP/GaInAsP separate confinement heterostructure structure multi-quantum well (SCH-MQW) laser diode (LD) on a directly InP/Si substrate. InP/Si substrate was prepared by the hydrophilic bonding of a thin InP film (1 µm) and silicon substrate with annealing at 400 °C. After crystal growth of the SCH-MQW laser structure on the InP/Si substrate, the surface was mirror-like and without any cross hatches or dislocations. Room temperature pulsed current lasing was then achieved using a Fabry-Perot cavity LD with a threshold current density of 2.85 kA/cm2.

Quantum effect on characteristics of semiconductor ring laser

A bistable semiconductor ring laser (SRL) with two counter propagation modes has been triggered by optical pulse injection which added to the initial nonlasing mode. As the optical pulse injection (OPI) has an important role in switching and lasing of SRL, we have to find a reliable area to achieve its amplitude and frequency. Numerical results show an increase in amplitude of OPI leading to switching time decreasing as well as an increase to amplitude oscillation. It is shown that in order to prevent the oscillation in laser output characteristic, the OPI power must be less than 2 mW. We have also investigated the effect of quantum wells on active region structure of SRL. It is obvious by increasing the quantum well numbers the output optical power has been increased and the switching time has been decreased. The main advantage of this research work is to apply separate confinement heterostructure (SCH) to multi quantum well (MQW) structure to extract numerical model for amplitude and phase of SCH-SRL. Using SCH in MQW-SRL active region will increase the output power to 0.8 mW and decrease threshold current to 12 mA.

Graded-Index Separate Confinement Heterostructure AlGaN Nanowires: Toward Ultraviolet Laser Diodes Implementation

High-density dislocations in materials and poor electrical conductivity of p-type AlGaN layers constrain the performance of the ultraviolet light emitting diodes and lasers at shorter wavelengths. To address those technical challenges, we design, grow, and fabricate a novel nanowire structure adopting a graded-index separate confinement heterostructure (GRINSCH) in which the active region is sandwiched between two compositionally graded AlGaN layers, namely, a GRINSCH diode. Calculated electronic band diagram and carrier concentrations show an automatic formation of a p–n junction with electron and hole concentrations of ∼1018 /cm3 in the graded AlGaN layers without intentional doping. The transmission electron microscopy experiment confirms the composition variation in the axial direction of the graded AlGaN nanowires. Significantly lower turn-on voltage of 6.5 V (reduced by 2.5 V) and smaller series resistance of 16.7 Ω (reduced by nearly four times) are achieved in the GRINSCH diode, compared with the ...

Numerical Simulation of the Current Dependence of Emission Spectra of High-Power Pulsed Lasers Based on Separate-Confinement Double Heterostructures

A new physical model is proposed for describing the observed current dependence of the emission spectra of high-power pulse lasers based on double separate-confinement heterostructures. The model takes into account the presence of isotype n–n heterojunctions at the interface between the waveguide and the active region. A numerical simulation of the lasing processes was performed. The resulting analytical current dependence of the 2D concentration of holes in the quantum well made it possible to evaluate for the first time the current dependence of the short-wavelength limit of the lasing spectrum. A good agreement was reached between the calculated and experimental characteristics.

Effect of GaN substrate thickness on the optical field of InGaN lasers diodes

In this work the influence of GaN substrate thickness on the near and far-field patterns of InGaN lasers structures is analyzed. In simulation a conventional separate confinement heterostructure of InGaN-MQW / GaN / AlGaN is considered. A fluctuating behavior is found, showing that for some values of the substrate thickness the near and far- field patterns can be optimized and there are critical values of the substrate thickness that produce the lowest values of the confinement factor and the higher values of the full wide half-maximum of the far field. It is also shown that by substituting the GaN contact layer by an AlxGa1-xN layer with a parabolic variation of the Al content it is possible to reduce the optical field leakage to substrate. Results indicated that properly choosing the thickness of the substrate and replacing the n-GaN contact layer by a graded-index (GRIN) AlxGa1-xN layer it is possible to improve both the confinement factor and Far field pattern in nitride lasers.

Design and analysis of InN − In0.25Ga0.75N single quantum well laser for short distance communication wavelength

A single quantum well semiconductor laser based on wurtzite-nitride is designed and analyzed for short distance communication wavelength (at around 1300 nm). The laser structure has 12 Å well layer of InN, 15 Å barrier layer of In0.25Ga0.75N, and 54 Å separate confinement heterostructure layer of GaN. To calculate the electronic characteristics of the structure, a self-consistent method is used where Hamiltonian with effective mass approximation is solved for conduction band while six-bands Hamiltonian matrix with k · p formalism including the polarization effect, valence-band mixing effect, and strain effect is solved for valence band. The interband optical transition elements, optical gain, differential gain, radiative current density, spontaneous emission rate, and threshold characteristics have been calculated. The wave function overlap integral is found to be 45.93% for TE-polarized structure. Also, the spontaneous emission rate is found to be 6.57 × 1027 s − 1 cm − 3 eV − 1 at 1288.21 nm with the carrier density of 5 × 1019 cm − 3. Furthermore, the radiative current density and the radiative recombination rate are found to be 121.92 A cm − 2 and 6.35 × 1027 s − 1 cm − 3, respectively, while the TE-polarized optical gain of the structure is 3872.1 cm − 1 at 1301.7 nm.

450 nm (Al,In)GaN optical amplifier with double 'j-shape' waveguide for master oscillator power amplifier systems.

In this paper we demonstrate 450 nm (Al,In)GaN graded index separate confinement heterostructure travelling wave optical amplifier with a double 'j-shape' waveguide. The length of the amplifier is 2.5 mm and the width of the ridge is 2.5 µm. The active region consists of three 3.5 nm thick quantum wells. The measured optical gain under CW operation in room temperature exceeded 29 dB for low power input signals. The saturation output power was 21 dBm for 400 mA driving current. The demonstrated amplifier, provides a good solution for the blue light, all nitrides, and master oscillator power amplifier systems.

Role of the electron blocking layer in the graded-index separate confinement heterostructure nitride laser diodes

In this work, we investigate the role of the electron blocking layer (EBL) in laser diodes based on a graded index separate confinement heterostructure. We compare two sets of devices with very different EBL aluminum composition (3% and 12%) and design (graded and superlattice). The results of electro-optical characterization of these laser diodes reveal surprisingly modest role of electron blocking layer composition in determination of the threshold current and the differential efficiency values. However, EBL structure influences the operating voltage, which is decreased for devices with lower EBL and superlattice EBL. We observe also the differences in the thermal stability of devices – characteristic temperature is lower for lasers with 3% Al in EBL.

Design of photonic crystal surface emitting lasers with indium-tin-oxide top claddings

Electrically pumped GaAs-based photonic crystal surface emitting lasers were fabricated using a simple fabrication process by directly capping the indium-tin-oxide transparent conducting thin film as the top cladding layer upon a photonic crystal layer. Optimization of the separate-confinement heterostructures of a laser structure is crucial to improving characteristics by providing advantageous optical confinements. The turn-on voltage, series resistance, threshold current, and slope efficiency of the laser with a 100 × 100 μm2 photonic crystal area operated at room temperature were 1.3 V, 1.5 Ω, 121 mA, and 0.2 W/A, respectively. Furthermore, we demonstrated a single-lobed lasing wavelength of 928.6 nm at 200 mA and a wavelength redshift rate of 0.05 nm/K in temperature-dependent measurements. The device exhibited the maximum output power of approximately 400 mW at an injection current of 2 A; moreover, divergence angles of less than 1° for the unpolarized circular-shaped laser beam were measured at various injection currents. Overall, the low threshold current, excellent beam quality, small divergence, high output power, and high-operating-temperature (up to 343 K) of our devices indicate that they can potentially fill the requirements for next-generation light sources and optoelectronic devices.

Численное моделирование токовой зависимости спектров излучения мощных импульсных лазеров, выполненных на основе двойных гетероструктур раздельного ограничения

AbstractA new physical model is proposed for describing the observed current dependence of the emission spectra of high-power pulse lasers based on double separate-confinement heterostructures. The model takes into account the presence of isotype n–n heterojunctions at the interface between the waveguide and the active region. A numerical simulation of the lasing processes was performed. The resulting analytical current dependence of the 2D concentration of holes in the quantum well made it possible to evaluate for the first time the current dependence of the short-wavelength limit of the lasing spectrum. A good agreement was reached between the calculated and experimental characteristics.

Degradation Mechanisms of Heterogeneous III-V/Silicon 1.55- $\mu \text{m}$ DBR Laser Diodes

This paper reports an extensive analysis of the degradation processes of heterogeneous III-V/Silicon infrared laser diodes designed for integrated telecommunications and interconnects. By submitting the devices to a series of constant current stress tests, a gradual degradation of the main device parameters was observed. In particular, in every stress scenario the devices under test showed: 1) an increase in the threshold current; 2) a decrease of the turn-ON voltage; and 3) an increase in the apparent carrier concentration within the space charge region. The variation of the electrical parameters (turn-ON voltage and apparent charge concentration) was found to be significantly correlated to the optical degradation for long stress times; the results support the hypothesis that degradation originates from an increase in the non-radiative recombination rate, possibly due to the diffusion of defects toward the active region of the devices. In order to investigate the physical origin of those defects, a capacitance deep level transient spectroscopy analysis was performed. The results indicate the presence of five different deep levels, with a main trap located around 0.43 eV above the valence band energy. This trap is compatible with an interface defect located between the In 0.53 Al x Ga 0.47-x As separate confinement heterostructure region and the InP layer.

Nanoscale effects on the thermal and mechanical properties of AlGaAs/GaAs quantum well laser diodes: influence on the catastrophic optical damage

In this work we study the catastrophic optical damage (COD) of graded-index separate confinement heterostructure quantum well (QW) laser diodes based on AlGaAs/GaAs. The emphasis is placed on the impact that the nanoscale physical properties have on the operation and degradation of the active layers of these devices. When these laser diodes run in continuous-wave mode with high internal optical power densities, the QW and guide layers can experiment very intense local heating phenomena that lead to device failure. A thermo-mechanical model has been set up to study the mechanism of degradation. This model has been solved by applying finite element methods. A variety of physical factors related to the materials properties, which play a paramount role in the laser degradation process, have been considered. Among these, the reduced thicknesses of the QW and the guides lead to thermal conductivities smaller than the bulk figures, which are further reduced as extended defects develop in these layers. This results in a progressively deteriorating thermal management in the device. To the best of our knowledge, this model for laser diodes is the first one to have taken into account low scale mechanical effects that result in enhanced strengths in the structural layers. Moreover, the consequences of these conflicting size-dependent properties on the thermo-mechanical behaviour on the route to COD are examined. Subsequently, this approach opens the possibility of taking advantage of these properties in order to design robust diode lasers (or other types of power devices) in a controlled manner.

Graded index separate confinement heterostructure transistor laser: analysis of various confinement structures

A new configuration of the confinement structure is utilized to improve optoelectronic performance, including threshold current, ac current gain, optical bandwidth, and optical output power of a single quantum well transistor laser. Considering the drift component in addition to the diffusion term in electron current density, a new continuity equation is developed to analyze the proposed structures. Physical parameters, including electron mobility, recombination lifetime, optical confinement factor, electron capture time, and photon lifetime, are calculated for new structures. Based on solving the continuity equation in separate confinement heterostructures, the threshold current reduces 67%, the optical output power increases 37%, and the −3 dB optical bandwidth increases to 21 GHz (compared to 19.5 GHz in the original structure) when the graded index layers of AlξGa1−ξAs (ξ:0.05→0 in the left side of quantum well, ξ:0→0.02 in the right side of quantum well) are used instead of uniform GaAs in the base region.

1.3-μm dual-wavelength DFB laser chip with modulation bandwidth enhancement by integrated passive optical feedback.

We report a 1.3-μm dual-wavelength distributed feedback (DFB) photonic integrated chip with modulation bandwidth enhancement using integrated optical feedback section. The dual-wavelength DFB lasers were realized using the upper separate confinement heterostructure (SCH) selective area growth (SAG) approach. A modified butt-joint technique was also adopted to achieve high-quality active-passive interface and minimize unintentional intra-cavity optical feedbacks. The fabricated photonic chip exhibited stable single mode operations with a wavelength separation of 2.06 nm. The 3-dB modulation bandwidth was enhanced through the photon-photon resonance effect with f3dB > 17 GHz and open eyes up to 25 Gbit/s for both channels were also obtained. The design can also be scaled up to higher channel counts and higher data rate.

Laser Arrays With 25-GHz Channel Spacing Fabricated by Combining SAG and REC Techniques

Multiwavelength laser arrays with 25-GHz channel spacing have been fabricated by upper separate confinement heterostructure (SCH) layer selective area growth (SAG) technique. The reconstruction equivalent chirp (REC) technique is used to introduce an equivalent phase shift into the grating structure, so that a high single longitude mode yield of lasers can be ensured. Because different emission wavelengths are realized through thickness modulation of the upper SCH layer by SAG, the sampling period in the REC technique is the same for all the lasers in an array, which may alleviate the effects of the facet phase on the emission wavelength. The fabricated laser arrays have less than 0.051 nm standard deviation of wavelength deviations. Only conventional photolithography process is needed, helping to lower the fabrication cost of the laser arrays.

A 1.3-μm four-channel directly modulated laser array fabricated by SAG-Upper-SCH technology

A monolithically integrated four-channel directly modulated laser (DML) array working at the 1.3-μm band is demonstrated. The laser was manufactured by using the techniques of selective area growth (SAG) of the upper separate confinement heterostructure (Upper-SCH) and modified butt-joint method. The fabricated device showed stable single mode operation with the side mode suppression ratio (SMSR) >35dB, and high wavelength accuracy with the deviations from the linear fitted values <±0.03nm for all channels. Furthermore, small signal modulation bandwidth >7GHz was obtained, which may be suitable for 40 GbE applications in the 1.3-μm band.

Performance improvement by enhancing the well-barrier hole burning in a quantum well semiconductor optical amplifier

In this paper, we demonstrated a novel physical mechanism based on the well-barrier hole burning enhancement in a quantum well (QW) semiconductor optical amplifier (SOA) to improve the operation performance. To completely characterize the physical mechanism, a complicated theoretical model by combining QW band structure calculation with SOA’s dynamic model was constructed, in which the carrier transport, interband effects and intraband effects were all taken into account. The simulated results showed optimizing the thickness of the separate confinement heterostructure (SCH) layer can effectively enhance the well-barrier hole burning, further enhance the nonlinear effects in SOA and reduce the carrier recovery time. At the optimal thickness, the SCH layer can store enough carrier numbers, and simultaneously the stored carriers can also be fast and effectively injected into the QWs.

On the problem of internal optical loss and current leakage in laser heterostructures based on AlGaInAs/InP solid solutions

Semiconductor lasers based on MOCVD-grown AlGaInAs/InP separate-confinement heterostructures are studied. It is shown that raising only the energy-gap width of AlGaInAs-waveguides without the introduction of additional barriers results in more pronounced current leakage into the cladding layers. It is found that the introduction of additional barrier layers at the waveguide–cladding-layer interface blocks current leakage into the cladding layers, but results in an increase in the internal optical loss with increasing pump current. It is experimentally demonstrated that the introduction of blocking layers makes it possible to obtain maximum values of the internal quantum efficiency of stimulated emission (92%) and continuouswave output optical power (3.2 W) in semiconductor lasers in the eye-safe wavelength range (1400–1600 nm).

Electro-optical modeling of high power semiconductor laser based on an InGaAs/GaAs/InGaP heterostructure

We present the electrical-optical modeling of a high power semiconductor laser diode for emission at 800 nm wavelength. We describe a thorough detailed procedure for the modeling of a semicondutor laser device with a Separate Confinement Heterostructure (SCH), based on the material alloys of III-V compounds families, InGaAsP/InGaAsP/InGaP on GaAs substrates. The heterostructure active region produces a peak emisson at 0.8 nm. The SCH heterostructure comprises a quntum well 100 A thick of InxGa1-xAsyP1-y (x = 0.14, y = 0.73) alloy. The quantum barriers layers comprise quaternary materials of composition InxGa1-xAsyP1-y (x = 0.39, y = 0.2). The confining layers of the quaternary SCH heterostrucure may involve higher gap materials, such as ternary InGaN or quaternary AlGaInP. Band gaps of quaternary materials in the well and confining layers of the SCH heterostructure correspond to wavelengths of 0.8 &#61549;m (Eg = 1.55 eV) and 0.69 &#61549;m (Eg = 1.8 eV), respectively.