Quantum-well Active Layer Research Articles

Fabrication of short GaAs wet-etched mirror lasers and their complex spectral behavior

A versatile fabrication technique for GaAs-AlGaAs wet-etched mirror lasers is presented. This technique works independently of the Al concentration in the cladding layers up to a value of 70%, and it requires four photolithography steps. Ridge waveguide lasers have been successfully processed using a double heterostructure (DHS) as well as graded index separate confinement heterostructures (GRINSCH) having different quantum-well (QW) active layers. This technique is used to fabricate short-cavity lasers in GRINSCH structures having GaAs multiple-quantum-well (MQW) or bulk active layers. Laser operation was obtained in a 29-/spl mu/m-long device using a 5-QW structure. Short lasers with QW active layers show a complex spectral behavior. These lasers operate at higher current densities (/spl sim/20 kA/cm/sup 2/) and emit light at more than one wavelength. This implies that higher order transitions are involved which is not the case when using a bulk GaAs active layer. Besides the two peaks corresponding to the n=1 and n=2 transitions, we found an intermediate peak which corresponds presumably to the forbidden transition E1-HH2.

Comprehensive modeling of diffused quantum-well vertical-cavity surface-emitting lasers

A numerical model for investigating the thermal, electrical, and optical characteristics of vertical-cavity surface-emitting: lasers (VCSELs) with a diffused quantum-well (QW) structure is presented. In the model, the quasi-three-dimensional (quasi-3-D) distribution of temperature, voltage and optical fields as well as the quasi-two-dimensional (quasi-2-D) diffusion and recombination of carrier concentration inside the QW active layer are calculated in a self-consistent manner. In addition, the quasi-3-D distribution of implanted ions before and after thermal annealing are computed. The variation of electrical conductivity and absorption loss as well as the influence of impurity induced compositional disordering on the optical gain and refractive index of the QW active layer are also taken into consideration. Using this model, the steady-state characteristics of diffused QW VCSELs are studied theoretically. It is shown that significant improvement of stable single-mode operation can be obtained using diffused QW structure.

Proposed enhancement of single mode operation in VCSELs using diffused quantum well structure

The use of interdiffused quantum wells to enhance single transverse mode operation in vertical cavity surface emitting semiconductor lasers is proposed and analysed theoretically. It is found that by introducing a step diffused quantum well structure inside the core region of a quantum-well active layer, the influence of self-focusing (due to carrier spatial hole burning and thermal lensing) on the profile of transverse modes can be minimized. Therefore, stable single-mode operation in vertical cavity surface emitting lasers can be maintained.

Threshold currents of nitride vertical-cavity surface-emitting lasers with various active regions

A detailed threshold analysis of room-temperature pulsed operation of GaN/AlGaN/AlN vertical-cavity surface-emitting lasers (VCSELs) is carried out. The model takes advantage of the latest results concerning gain in active regions, material absorption in the cladding layers, as well as cavity diffraction and scattering losses. The simulation showed that although VCSELs with single (S) or multiple (M) quantum-well (QW) active regions exhibit lower threshold currents, they are much more sensitive to any increase in optical losses than their bulk counterparts. In particular, decreasing the active region radius of gain-guided QW VCSELs below 5 μm (which increases diffraction losses) or increasing dislocation densities (which, in turn, raises scattering losses) gives an enormous rise to their threshold currents. Therefore small-size GaN VCSELs should have an index-guided structure. In the case of MQW VCSELs, the optimal number of quantum wells strongly depends on the reflectivities of resonator mirrors. According to our study, MQW GaN lasers usually require noticeably lower threshold currents compared to SQW lasers. The optimal number of QW active layers is lower in laser structures exhibiting lower optical losses. Although the best result occurred for an active region thickness of 4 nm, threshold currents for the various sizes differ insignificantly.

Uniform Fabrication of Highly Reliable, 50–60 mW-Class, 685 nm, Window-Mirror Lasers for Optical Data Storage

Uniform fabrication of highly reliable 50–60 mW-class 685 nm laser diodes (LDs) with a window-mirror structure has been realized by using selective solid-phase Zn diffusion and three-inch full wafer processing. A window-mirror structure at the LD mirror is formed by Zn-induced disordering of an ordered GaInP multiple quantum-well (MQW) active layer. High uniformity of characteristics such as the operating current and the far-field pattern has been obtained by realization of highly uniform Zn diffusion. A small astigmatic distance (ΔZ≦3 µ m), a low relative intensity noise (RIN≦-135 dB/Hz) and a high speed response (T r, T f≦1.2 ns) are obtained in addition to the high-power and high-temperature characteristics (70 mW, 80° C) in spite of the existence of the window structure. The LDs have exhibited reliable 6,000–10,000 h operation under the conditions of 60° C and 50–60 mW for the first time.

N -type delta doped strained quantum well lasers for improved modulation bandwidth

Improved dynamic properties of strained single quantum well (QW) lasers were obtained by the incorporation of an n-type δ doping at close proximity to the strained QW active layer. The resultant modulation bandwidth was almost doubled, from 3.5 GHz to more than 6.2 GHz. The increased modulation bandwidth is attributed to an improved carrier injection resulting from the enhancement of the carrier transit time into the QW, as well as a decrease in the significance of the adverse contribution of carrier transport effects.

Active Anti-Guide Vertical Cavity Surface Emitting Lasers with Diffused Quantum Wells Structure

AbstractThe enhancement of single transverse mode operation in vertical cavity surface emitting lasers by using interdiffused quantum wells is proposed and analyzed. It is observed that the influence of self-focusing (arising from carrier spatial hole burning and thermal lensing) on the profile of transverse modes can be minimized by introducing a step diffused quantum wells structure inside the core region of quantum-well active layer. Stable single-mode operation in vertical cavity surface emitting lasers can also be maintained.

Room-temperature pulsed operation of 1.5-μm vertical cavity lasers with an InP-based Bragg reflector

We report on a 1.5-/spl mu/m vertical-cavity laser that utilizes one GaInAsP-InP and one Si-SiO/sub 2/ mirror in combination with a strain-compensated GaInAsP quantum-well active layer. Pulsed lasing operation was achieved in a temperature range from -160 to +43/spl deg/C. The lasers exhibit 30-mA pulsed threshold current at room temperature. CW operation was obtained up to -25/spl deg/C.

Bipolar quantum-transport modeling of carrier injection into a SCH-quantum-well laser

A quantum mechanical model of carrier transport in separate confinement heterostructure (SCH) quantum-well lasers based on the Wigner function is presented for the first time. In the simulation, the three quantum Liouville equations with respect to the Wigner functions defined for electron, heavy-hole, and light-hole are solved simultaneously with the Poisson's equation to consider self-consistency in potential, As a simulation model, InGaAsP-InGaAs SCH quantum-well lasers are considered. The carrier injection into single and double quantum-well lasers is simulated. It is demonstrated that the amount of electrons and holes injected into the single quantum-well active layer is not equal in general if the quantum transport is considered. In the double quantum-well structure, the bottleneck phenomenon of heavy-hole injection into the second well and the quite different shape of heavy-hole density profiles in the two wells are simulated.

Transverse-mode & polarization characteristics of double-fused 1.52 μm vertical-cavity lasers

We report on the transverse mode and polarization characteristics of a novel 1.52 μm vertical-cavity laser that utilizes an InGaAsP strain-compensated quantum-well active layer and two AIAs/GaAs quarter-wave mirrors. The 6 and 8 μm diameter devices exhibit room-temperature pulsed threshold currents as low as 4 mA, and a maximum output power of 14 mW was measured on a 60 μm diameter device.

Superluminescent diodes based on single-quantum-well (GaAl)As heterostructures

Theoretical and experimental investigations were made of the power, spectral, and polarisation characteristics of superluminescent diodes based on (GaAl)As heterostructures with separate confinement and a quantum-well active layer. The technical characteristics of these diodes were not inferior to those of superluminescent diodes based on traditional double-sided heterostructures. The new diodes were superior to the traditional heterostructures in respect of the half-width of the emission spectrum which was up to 100 nm, corresponding to a coherence length less than 7 μm. Test samples of light-emitting modules based on the investigated diodes were constructed.

Room-temperature continuous-wave operation of 1.54-μm vertical-cavity lasers

We report on the room-temperature continuous-wave operation of vertical-cavity lasers operating at 1.54 μm. The devices use a 7 strain-compensated quantum-well active layer sandwiched between two Al(Ga)As-GaAs quarter-wave mirrors joined by wafer fusion. Five device sizes between 8 and 20 μm were found to operate continuously at room temperature (23/spl deg/C), The lowest room-temperature continuous-wave threshold current of 2.3 mA was measured on an 8-μm diameter device, while the highest continuous-wave operating temperature of 33/spl deg/C was measured on a 12-μm device.

Control of light-output polarization for surface-emitting-laser type device by strained active layer grown on misoriented substrate

We propose and demonstrate control of light-output polarization for surface-emitting laser-type devices by using strained quantum-well active layers grown on a misoriented substrate. This structure has slightly asymmetric strain tensor elements on the surface plane. Due to orbital-strain interaction, the valence band structures change and the optical transition matrix element depends on the polarization of the light. Here, theoretical analysis and experimental results on the direction of misorientation are described, and it is shown that how the polarization of the light-output is related to asymmetry in strain tensors. For the devices, which have In/sub 0.2/Ga/sub 0.8/As active layers grown on a 2-degree-off-(100) GaAs substrate toward (111)B, the light-output is polarized in [01~1] with the reproducibility of as high as 88%. This highly controlled polarization is probably due to the combination of converse piezoelectric effect and asymmetry in the lattice mismatch on the surface caused by misorientation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Characteristics of laser diodes with a partially intermixed GaAs-AlGaAs quantum well

Laser diodes (LD's) with a partially intermixed quantum-well (QW) active layer are fabricated by Zn out-diffusion from a p-cladding layer to the QW region. The dependencies of the degree of intermixing, measured by the photoluminescence (PL) shift, on Zn concentration of the p-cladding layer (P/sub clad/) and the Al content of the guiding layer (X/sub g/) in a separate-confinement-heterostructure (SCH) are investigated. P/sub clad/ changes in the range from 1/spl times/10 /sup 18/ cm/sup -3/ to 4/spl times/10/sup 18/ cm/sup -3/ and X/sub g/ changes in the range from 0.21-0.37. When P/sub clad/ is 2/spl times/10/sup 18/ cm/sup -3/ and X/sub g/ is 0.37, large bandgap energy shift of 96.1 meV is observed. The lasing wavelengths of the LD's, with the partially intermixed QW, are blue-shifted linearly with increasing P/sub clad/ and X/sub g/. For the bandgap energy shift of 66.8 meV by PL, the threshold current density is increased by 33% from that of the nonintermixed LD. Reliability of LD's with the partially intermixed QW is investigated for the first time. In spite of a large degree of intermixing the reliability of the LD with the partially intermixed QW of 66.8 meV energy shift by PL is the same as the nonintermixed one, which is confirmed by the aging test of 2500 hours at 45/spl deg/C with the output power of 1 W under CW operation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Transverse-mode and polarisation characteristics of double-fused 1.52 [micro sign]m vertical-cavity lasers

The authors report the transverse mode and polarisation characteristics of a novel 1.52 µm vertical-cavity laser that utilises an InGaAsP strain-compensated quantum-well active layer and two AlAs/GaAs quarter-wave mirrors. The devices exhibit 4 mA room-temperature pulsed threshold current and 14 mW output power.

Spectral characteristics of single-frequency quantum-well heterolasers

Precision measurements and a comparative analysis were made of the emission spectra of GaAs/AIGaAs and InGaAs/GaAs heterostructure injection lasers with quantum-well active layers and plane—plane cleaved cavities. Attention was focused on the correlation between the linewidth enhancement factor and the parameters of single-frequency lasing. Single-frequency emission at λ = 975 nm was observed for a quantum-well laser with strained active layers and a cw output power in excess of 100 mW was reached when the side longitudinal modes were suppressed by more than 30 dB.

Measurement of differential gain and linewidth enhancement factor of 1.5-μm strained quantum-well active layers

The differential gain a and the linewidth enhancement factor /spl alpha/ of 1.5-/spl mu/m strained quantum well active layers mere measured as functions of the carrier density and the wavelength. Both a and /spl alpha/ of compressively strained multiple-quantum-well (CS-MQW) active layers reveal a carrier-density dependence which is stronger than that of unstrained multiple quantum-well (MQW) and tensile-strained single-quantum-well (TS-SQW) active layers. The improvement in these parameters is achieved only when the carrier density is low. On the other hand, in the case of TS-SQW active layers, the carrier density dependence is much smaller, and the differential gain is improved significantly.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Saturation characteristics of Ga/sub 0.68/In/sub 0.32/As/GaInAsP/InP tensile-strained quantum-well semiconductor laser amplifiers with tapered-waveguide structures

With an aim toward a high-saturation power operation, a tapered-waveguide traveling-wave semiconductor laser amplifier (SLA) with a Ga/sub 0.68/In/sub 0.32/As/GaInAsP/InP tensile-strained quantum-well (QW) structure was investigated and realized for the first time. In spite of the high differential gain in the tensile-strained QW active layer, a high-saturation-output power of 18.5 dB (1 mW) (71 mW) and a high-maximum-output power of 20.4 dB(1 mW) (110 mW) were obtained with a narrow single-lobed beam-divergence property. These results indicate that the saturation performances of SLA's with tensile-strained active layers can be improved by the tapered-waveguide structures.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Directional pattern and other output properties of a quantum-well injection laser for the 780-nm spectral region

An optical model is constructed for a GaAlAs/GaAs stripe-geometry laser heterostructure with a ridge-waveguide configuration in the p-type emitter layer. This waveguide configuration provides lateral optical confinement. The directional characteristics of the output are found as a function of the parameters of the structure. The quantum-well active layer is in a three-layer waveguide (in a separate-confinement structure). Laser structures were fabricated experimentally by MOCVD epitaxy followed by ion-chemical etching and vacuum deposition of zinc selenide on the mesa stripes. Low-threshold lasers with a cw, single-frequency power up to 40 μW were obtained. In single-spatial-mode operation, a power up to 80 μW was achieved at a wavelength of 780 nm. Windows of ZnSe were grown on the laser facets to improve the optical strength.

High-power 780 nm AlGaAs quantum-well lasers and their reliable operation

A high-power laser in the 780-nm wavelength region was realized by introducing an AlGaAs ternary alloy quantum-well structure. Since there is no axial structure, high reproducibility is expected. By applying the quantum-well structure to the AlGaAs ternary alloy wells, a reduction in the operation current of a laser which oscillates in the 780-nm wavelength region can be achieved. A reduction of the optical power density in the direction perpendicular to the junction plane is examined to lessen facet degradation. Investigations focus on the characteristic temperature and catastrophic optical damage (COD) level. It is found that a triple quantum-well (TQW) active layer structure has superior characteristics for high-power operation. Stable operation for over 1000 h under 50 degrees C and 60 mW conditions was achieved. A relatively high characteristic temperature of around 150 K was also obtained. The results of an aging test are provided. >