Multiquantum-well Layers Research Articles

MOVPE growth of strained InGaAs/lnAIAs MQWs for a polarization-insensitive electroabsorption modulator

Metalorganic vapor phase epitaxial growth of a strained InGaAs/lnAIAs multiquantum well (MQW) structure was carried out for optical electroabsorption modulators. A high-quality MQW layer can be grown by introducing compressive strain into InAlAs barrier layers against tensile-strained well layers. We have also demonstrated strained InGaAs/lnAIAs MQW electroabsorption modulators with polarization insensitivity by using these layers and have obtained a highquality modulator with a low driving voltage of 1.7 V and a wide 3-dB bandwidth of over 20 GHz.

Simulation of enhanced plasma effect wavelength tunable lasers

The enhanced plasma effect (EPE) laser is a novel tunable multiquantum well (MQW) distributed feedback (DFB) laser with a thick reservoir layer between p-cladding and MQW layers. Performance of the EPE laser has been simulated by LDSCOPE (laser diode simulator by self-consistent opto-electronic model). Fast wave length shift due to the plasma effect is enhanced by increased carrier density change in the reservoir owing to the carrier transport effect. The calculated threshold and FM efficiency are in good accordance with those obtained experimentally. Calculated results suggest that a tuning range over 2.5 nm due to the plasma effect would have been obtained in the fabricated EPE laser with a 0.6 mu m reservoir for the bias current range below 300 mA if it had not been for leakage current. A reservoir thicker than the diffusion length does not lead to a wider tuning range, because of carrier recombination in the reservoir. A thin barrier layer inserted between the reservoir and the MQW layer, however, will improve the carrier distribution in the reservoir, so that the tuning range may be expanded by 20%.

Investigation of tensile-strained InGaAlP multiquantum-well active regions by photoluminescence measurements

The use of a tensile-strained multiquantum-well (MQW) active region in 630-nm-band InGaAlP MQW laser diodes is investigated through photoluminescence (PL) measurements. The critical conditions for lattice relaxation of strained MQW layers are also discussed. Emissions due to electron–heavy-hole recombination and electron–light-hole recombination are observed in the PL spectrum. A large energy difference (about 38 meV) is found between the two peaks, and radiative recombination is dominant in the MQW structure. These are thought to decrease the threshold current of tensile-strained MQW laser diodes. The MQW active region is thought to be extremely close to the critical conditions for lattice relaxation, but no adverse effects on optical properties are observed. It is concluded that such a tensile-strained MQW active region has advantages for use as the active region of 630-nm-band laser diodes.

Dependence of device characteristics on quantum well thickness in ZnSe/ZnCdSe multi-quantum well blue-green laser diodes

ZnSe/Zn 0.85Cd 0.15Se multi-quantum well (MQW) diode structures with different well thicknesses ( L w) in the range of 6–13 nm were fabricated, and device characteristics of the diodes were studied in terms of crystalline quality of the MQW layers. In order to investigate the relationship between the device characteristics and the crystalline quality of the MQW layers, the intensity of spontaneous emission from MQW diode structures was measured. The emission intensity increased with increasing L w and showed a maximum value at L w = 10 nm, followed by rather rapid reduction of the emission intensity at L w > 10 nm. This decrease of emission intensity is suggested to be due to the lattice relaxation caused by dislocation formation at the interface taking account of critical thickness of the MQW structure. The lasing characteristics of ZnSe/ZnCdSe MQW blue-green laser diodes are also described.

Theoretical calculations of the transition energies of a hydrogenic impurity in GaAs/GaAlAs multi-quantum wells in magnetic fields applied at any angle

Calculations are made of the energies of the dominant transition (1s to 2p+1-like) of a hydrogenic donor impurity in a multi-quantum-well (MQW) system subject to a magnetic field applied at an angle theta to the direction of growth of the MQW layers. The model used involves constructing suitable basis states, and then performing a matrix diagonalization procedure. The results are compared to the available experimental data, including the extreme cases of fields perpendicular ( theta =0 degrees ) and parallel ( theta =90 degrees ) to the layers. The results are also found to compare well with the results of existing variational calculations.

Proposal and realisation of new type distributed reflector (DR) laser with multiquantum-well structure

A new type distributed reflector (DR) laser, which uses the multiquantum-well (MQW) waveguide as both the active and passive distributed reflector, is proposed and realised. Its superior lasing characteristics are experimentally confirmed by introducing GaxIn1-xAs/GaInAsP compressive strained MQW layers; the characteristics include a narrow linewidth of 743 kHz, high submode suppression-ratio (SMSR) of >41dB at 2.2 times the threshold, and about two times larger differential quantum efficiency ηdf than that of DFB lasers.

High static performance GaInAs-GaInAsP SCH MQW 1.5 mu m wavelength buried ridge stripe lasers

The potential advantages of GaInAs/InP multiquantum well (MQW) structures over bulk material for improving the static properties of buried heterostructure (BH) lasers are demonstrated. Using a highly uniform metalorganic vapor phase epitaxy (MOVPE) growth, an optimized simple separate confinement heterostructure (SCH) MQW layer stack, and the buried ridge stripe (BRS) structure, improved static performances over any bulk or unstrained MQW long wavelength laser were obtained. An extremely low threshold below 2 mA was obtained in short cavity lasers, the threshold current was only 10.6 mA and 110 mW continuous-wave (CW) maximum optical power was observed using 90%/10% reflectivity coatings.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Ordered Structure in GalnP/AIGalnP Quantum Wells and p-Doped Multiquantum Well AIGalnp Laser Diodes

ABSTRACTZinc doping is performed on the GalnP/AIGalnP multiquantum well (MQW) structure with the aim of dissolving the ordered atomic arrangement which results in higher quantum levels and therefore shorter lasing wavelengths. It is shown that the photoluminescence (PL) peak wavelength gradually shortens with doping and decreases by 20 nm when the hole concentration reaches 1×1018 cm−3, while the PL relative intensity becomes half that of an undoped MQW layer. Therefore, a moderate level of zinc doping of around 4∼5×1017 cm−3 is desirable to shorten the PL wavelength without decreasing the crystal quality. Transmission electron nano-diffraction patterns confirm that the ordered structure in the MQW layers disappears as the hole concentration increases. On the basis of this data, uniformly p-doped and modulation p-doped MQW laser diodes are fabricated and their characteristics are compared with the undoped MQW lasers. CW operation is achieved at wavelengths of 631 to 633 nm, which is 10 nm shorter than the 643 nm in an undoped MQW laser. Comparatively low threshold currents of 73 and 88 mA are attained for uniformly p-doped and modulation p-doped MQW lasers, respectively. However, they are about 20∼30 mA higher than those of the undoped MQW lasers. This results from the large overflow of electrons from the active layer, and the fact that the differential gain becomes smaller in the 630-nm band.

LPE growth of InP and InGaAs on MQW layers below 500°C

InP and InGaAs layers were grown on multiquantum well (MQW) layers by LPE below 500°C without thermal degradation. The LPE growth of InP and InGaAs below 500°C is slow, but fast enough to fabricate the device. The carrier concentration of InP and InGaAs was controlled by doping below 500° C. It was confirmed that the thermal process in LPE growth of InGaAs on MQW layers below 500° C does not affect on the MQW structure.

LPE growth and characterization of InGaAsP/InP multiquantum well epitaxial layers

This paper presents very thin InGaAsP/InP layers grown by the LPE-sliding growth technique and the characterization of the fabricated multiquantum well (MQW) layers. In the LPE growth mechanism of the very thin layer, the transient region having a thickness of 60 to 75 Å is formed at the onset of the growth under nonequilibrium conditions of the solid-liquid interface, while a very thin layer is grown under diffusion-limited conditions. For MQW layers, the degeneration split between the heavy- and light-hole levels has been recognized from the photoluminescence measurements, and ±1st and ±2nd order satellite peaks of the superlattice have been observed in the rocking curves of the double X-ray diffraction. Furthermore, it has been recognized that the lattice constant of the very thin layers in the LPE-grown InGaAsP/InP MQW layers was shifted to that of the InP layers by the relaxation of the strain at the heterointerfaces.