Quantum Wire Lasers Research Articles

AlGaAs/GaAs quantum wire lasersfabricated by flow rate modulation epitaxy

AlGaAs/GaAs quantum wire lasers, with three quantum wires (QWRs) of almost identical physical size, have been fabricated by flow rate modulation epitaxy. Room temperature lasing from the ground state electron and heavy-hole (1e-1hh) transition of the QWRs has been observed for the first time. Typical threshold currents of 6 mA and extremely minor wavelength shifts in emission spectra have been obtained.

Super-flat (411)A interfaces and uniformly corrugated (775)B interfaces in GaAs/AlGaAs and InGaAs/InAlAs heterostructures grown by molecular beam epitaxy

Extremely flat interfaces, i.e. effectively atomically flat interfaces over a wafer-size area were realized in GaAs/AlGaAs quantum wells (QWs) grown on (411)A GaAs substrates by molecular beam epitaxy (MBE). These flat interfaces are called as “(411)A super-flat interfaces”. Besides in GaAs/AlGaAs QWs, the (411)A super-flat interfaces were formed in pseudomorphic InGaAs/AlGaAs QWs on GaAs substrates and in pseudomorphic and lattice-matched InGaAs/InAlAs QWs on InP substrates. GaAs/AlGaAs resonant tunneling diodes and InGaAs/InAlAs HEMT structures with the (411)A super-flat interfaces were confirmed to exhibit improved characteristics, indicating high potential of applications of the (411)A super-flat interfaces. High density, high uniformity and good optical quality were achieved in (775)B GaAs/(GaAs)m(AlAs)n quantum wires (QWRs) self-organized in a GaAs/(GaAs)m(AlAs)n QW grown on (775)B GaAs substrates by MBE. The QWRs were successfully applied to QWR lasers, which oscillated at room temperature for the first time as QWR lasers with a self-organized QWR structure in its active region. These results suggest that MBE growth on high index crystal plane such as (411)A or (775)B is very promising for developing novel semiconductor materials for future electron devices.

Self-organized GaAs quantum-wire lasers grown on (775)B-oriented GaAs substrates by molecular beam epitaxy

Self-organized GaAs/(GaAs)4(AlAs)2 quantum-wire (QWR) lasers were grown on (775)B-oriented GaAs substrates by molecular-beam epitaxy. The QWRs were naturally formed at thick parts in the GaAs/(GaAs)4(AlAs)2 quantum well with a corrugated AlAs-on-GaAs upper interface and a flat GaAs-on-AlAs lower interface. The density of the QWRs was as high as 8×106 cm−1. Stripe-geometry lasers with the self-organized (775)B GaAs/(GaAs)4(AlAs)2 QWRs as an active region oscillated at 20 °C with threshold current densities of about 3 kA/cm2 for uncoated mirrors.

Temperature Dependence of Internal Quantum Efficiency of 20-nm-Wide GaInAsP/InP Compressively-Strained Quantum-Wire Lasers

We evaluated the temperature dependence of the internal quantum efficiency of 1.5-µm-wavelength GaInAsP/InP compressively-strained 20-nm-wide quantum-wire lasers from the cavity length dependence of the differential quantum efficiency. As a result, high internal quantum efficiency ηi∼1.0 was obtained at T<200 K, which decreased with an increase in temperature.

Band structures and optical properties of Ga1−xInxAs quantum wires grown by strain-induced lateral ordering

Band structures and optical matrix elements of strained multiple quantum wires (QWRs) are investigated theoretically via the effective bond-orbital model, which takes into account the effects of valence band anisotropy and the band mixing. In particular, the Ga1−xInxAs QWRs grown by strain-induced lateral ordering (SILO) are considered. Recently, long wavelength Ga1−xInxAs QWR lasers have been fabricated via a single step molecular beam epitaxy technique which uses the SILO process [S. T. Chou, K. Y. Cheng, L. J. Chow, and K. C. Hsieh, Appl. Phys. Lett. 17, 2220 (1995); J. Appl. Phys. 78, 6270 (1995); J. Vac. Sci Technol. B 13, 650 (1995); K. Y. Cheng, K. C. Hsien, and J. N. Baillargeon, Appl. Phys. Lett. 60, 2892 (1992)]. Low threshold current and high optical anisotropy have been achieved. Multiaxial strains [combinations of biaxial strains in the (001) and (110) planes] for QWRs are considered. Our calculated anisotropy in optical matrix elements (for light polarized parallel versus perpendicular to the QWRs’ axis) is in good agreement with experiment. We also find that the strain tends to increase the quantum confinement and enhance the anisotropy of the optical transitions.

ADVANCED CONCEPTS IN INTERSUBBAND UNIPOLAR LASERS

Advanced concepts in intersubband optical emission for mid-infrared (MIR) and far-infrared (FIR) lasers in nanostructures are presented. Electronic tunability of low dimensional systems, and new simulation techniques are implemented for engineering electron scattering time with phonons and improving laser performances. We successively describe the operation of an optically pumped "quantum fountain laser" made of asymmetric coupled quantum well structures, a FIR quantum wire laser pumped by optic phonons and an electrically tunable, mode locked FIR quantum dot laser.

Near-field scanning optical microscopy studies of V-grooved quantum wire lasers

Detailed near-field scanning optical microscopy studies of GaAs/AlGaAs V-grooved quantum wire lasers at room temperature were performed. We measured the spectrally resolved near-field intensity distributions, emitted from the complex epitaxially grown optical waveguide in the V groove with a spatial resolution of ∼0.1 μm. Distinct regions emitting at different wavelengths were identified, and a heart shaped modal distribution of less than 0.5 μm in diameter was measured and well matched the calculated light distribution of this structure.

GaInAsP/InP Compressively Strained Quantum-Wire Lasers Fabricated by Electron Beam Lithography and 2-Step Organometallic Vapor Phase Epitaxy

GaInAsP/InP Compressively Strained Quantum-Wire Lasers Fabricated by Electron Beam Lithography and 2-Step Organometallic Vapor Phase Epitaxy

Stimulated emission in ridge quantum wire laser structures measured with optical pumping and microscopic imaging methods

We report the observation of stimulated emission in ridge quantum wire (QWR) structures at temperatures from 4.7 to 290 K. To examine the origin of the stimulated emission, the spatially and spectrally resolved microscopic images of the emission were measured. It was most likely attributed to the optical transition between the excited states in QWRs.

Self-organised InGaAs quantum wire lasers on GaAsmulti-atomic steps

The authors report the first successful demonstration of self-organised InGaAs quantum wire (QWR) laser diodes (LDs) utilising GaAs multi-atomic steps at 77 K by pulsed current injections. The lasing wavelength of InGaAs QWR-LDs is consistent with the peak position of photoluminescence spectra at 77 K. When a cavity direction is perpendicular to the QWR's array direction, the threshold current density of InGaAs QWR LDs is smaller than that of quantum well LDs.

The directionality of quantum confinement on strain-induced quantum-wire lasers

Optical properties of Ga0.47−xIn0.53+xAs (x∼0.14) multiple-quantum-wire (MQWR) lasers prepared by the strain-induced lateral-layer ordering process were studied. A typical ratio of threshold current density, ∼10, was observed from the GaInAs MQWR lasers with contact stripes aligned to the [110] ([110] MQWR laser) and the [1̄10] ([1̄10] MQWR laser) directions. The threshold current density of the [110] MQWR laser is ∼30% lower than that of a Ga0.47In0.53As multiple-quantum-well (MQW) reference laser. The 77 K lasing wavelengths were 1.46, 1.57, and 1.69 μm for the MQW laser, the [1̄10] and [110] MQWR lasers, respectively. This strong anisotropy of threshold current densities and lasing wavelengths is the first direct evidence of the directionality of two-dimensional quantum confinement in the MQWR structure.

Highly uniform and high-density GaAs/(GaAs)4(AlAs)2 quantum wires grown on (775)B-oriented GaAs substrates by molecular beam epitaxy

Extremely uniform and high-density GaAs/(GaAs)4(AlAs)2 quantum wires (QWRs) were self-organized in a thin GaAs/(GaAs)4(AlAs)2 quantum well grown on a (775)B GaAs substrate with a regularly corrugated AlAs–on–GaAs interface and a flat GaAs–on–AlAs interface by molecular beam epitaxy. A strong photoluminescence (PL) peak at λ=692 nm from the GaAs/ (GaAs)4(AlAs)2 QWRs showed large polarization anisotropy [P=(I∥−I⊥)/(I∥+I⊥)=0.19]. A full width at half-maximum of the PL peak from the QWRs was as small as 15 meV at 14 K, which is smaller than those of any self-organized GaAs/AlGaAs QWRs reported so far. Density of the QWRs ( 8×105 QWRs/cm) is the same as the highest ever reported. These results indicate that the QWRs grown on the (775)B GaAs substrate meet requirements for applications to QWR lasers (high uniformity, high density, high optical quality, and simple fabrication process).

V-Grooved [formula omitted] quantum wire laser array confined by junction-isolation stripes

A new GaAs AlGaAs quantum wire laser array (QWLA) confined by p- n junction-isolation stripes is reported. The QWLA is fabricated with 1.5 μm wide stripe-channels through the quantum wire (QWR) active regions using two-step MOCVD growth with a wet etching technique. Prior to the device fabrication, active channel- and leakage-current are calculated using a d.c. equivalent circuit to quantitatively estimate the current-confinement effect. QWLA consisting of 10 QWRs has currently demonstrated a maximum output power as high as 18.2 mW at 385 mA and a threshold current density as low as 0.23 kA m −2 facet −1 under room temperature pulsed operation.

Reduced threshold current density due to excitonic optical gain in the presence of dislocations and surface states in tensile strained ZnCdSe quantum wire lasers

Higher binding energies (30–60 meV) in II–VI wide-gap materials result in large exciton densities, making optical transitions due to excitons dominant over free electrons and holes. Optical gain and threshold current densities in ZnCdSe based multiple quantum wire lasers are computed including the effect of strain. It is found that the tensile-strained quantum wires yield lower threshold current densities than compressive strained or unstrained structures. The calculated threshold current density for a defect free tensile-strained ZnCdSe–ZnMgSSe quantum wire laser, realized on an InP substrate, has been computed to be 58 A/cm2. The exciton transitions assist in lowering the threshold current density which is adversely affected by the presence of dislocations and surface states. It is found that the threshold current density would increase to 435 A/cm2 assuming 1017 cm−3 trapping levels due to dislocations and surface states. However, taking into account the exciton transitions, the threshold current density is reduced to 79 A/cm2 when assuming the same trapping level density.

Carrier capture times in quantum-well, -wire, and -box distributed-feedback lasers characterized by dynamic lasing emission measurements

We report experimental and theoretical studies of carrier capture times in low-dimensional semiconductor distributed feedback lasers with three different typical active region structures: quantum well (QW), wire, and box. The total effective carrier capture times of the lasers are directly determined by means of dynamic lasing emission measurements. By systematical comparison of QW, wire and box lasers, we evidence a strong dependence of the total effective carrier capture time on the packing density of the active region, which indicates the significant contribution of the local quantum capture time to the total effective carrier capture time, as revealed firstly by Kan et al. (1993). The intrinsic local carrier quantum capture time can be deduced from this kind of study. The determined local quantum carrier capture time for the InGaAs-InGaAsP QW laser is about 3 ps at 2 K, which is well consistent with a detailed quantum mechanics calculation. Furthermore, by comparison of box lasers with an approximate equal box size (70 nm) but different box densities, we find that the determined local quantum capture time of the box lasers is only about 2.4 ps at low temperature. We believe that this is a direct experimental indication of the existence of an efficient channel for carrier capture and relaxation in the investigated quantum-box system. The systematic comparison of QW, wire and dot lasers reveals the dominant limitation of the geometry effect on the high speed modulation of quantum wire and dot lasers, except when the quantum wires and dots are packed with a quite high density.

Fabrication of V-grooved inner stripe GaAs-AlGaAs quantum-wire lasers

V-grooved inner stripe (VIS) GaAs-AlGaAs quantum-wire (QWR) lasers were successfully fabricated by, combining two-step metalorganic chemical vapor deposition (MOCVD) growth with a wet-etching technique. In order to achieve low threshold current density and high reliability, a conductive stripe width (W), a thickness (t/sub p-CBL/), and a doping concentration (n/sub p-CBL/) of the p-GaAs current-blocking layer (CBL) were determined to be W=1.2 /spl mu/m, t/sub p-CBL/=2 /spl mu/m, and n/sub p-CBL/=1/spl times/10/sup 18/ cm/sup -3/. The leakage currents passing through the CBL were also estimated using a modified P-SPICE. Thus far, a threshold current of 45 mA and an output power of 4 mW at 51 mA have been achieved under room-temperature pulsed operation for some devices with uncoated facets.

A highly luminescent crescent-shaped tensile-strained quantum wire laser structure

Abstract We report a highly luminescent crescent-shaped tensile-strained GaAsP AlGaAs quantum wire (QWR) laser structure on 3 μm periodic V-grooves grown by low-pressure (100 Torr) metalorganic vapor phase epitaxy (MOVPE). Photoluminescence studies show that carriers are efficiently captured from neighboring quantum well layers (QWLs) into QWRs, which give efficient luminescence. The QWR light emitting diode (LED) shows polarization insensitivity resulting from the tensile strain properties of the QWR structure.

A short-period GaAs-AlGaAs quantum-wire array laser with a submicrometer current blocking layer

The structure and device characteristics of a 700-nm-pitch GaAs-AlGaAs quantum-wire array laser (QWAL) with a dielectric defined current blocking layer are reported. The high wire density of the QWAL has been expected to yield more efficient carrier capture, but large spacing between the quantum wires was found to deteriorate the laser characteristics. In this work, we have improved electrical confinement into the active regions by incorporating a SiO/sub 2/ film onto the large spacing. Room-temperature pulsed operation with an output power of 9 mW at 191-mA injection current was achieved for a 200/spl times/500 /spl mu/m laser with uncoated facet. The threshold current density was 0.14 kA/cm/sup 2/. The dependence of the threshold current and the maximum power on the cavity length and width was also studied.

QUANTUM WELL LASERS AND THEIR APPLICATIONS

Quantum well lasers have attracted a great deal of attention by their many advantages such as low threshold current density, excellent temperature feature, high modulation rate and wavelength adjustability etc. The investigation on quantum well laser in mainland China started in the early 80s. AlGaAs/GaAs QW laser diode and InGaAs/GaAs strained layer QW laser diode have been developed using MBE technology with extremely low threshold current and high T0. Now the growth technologies for QW structure have been expanded to MOCVD technology. Emission wavelengths, on longer wavelength sides have been expanded up to 1.3 µm and 1.55 µm with InGaAsP/InP material system for application in optical fiber communication. On shorter wavelength sides, the emission wavelength has been expanded to lower than 670 nm, for applications in optical information processing. The characteristics of these devices will be demonstrated in this paper. The QW-DFB LD and low-dimension quantum wire and quantum dot lasers are under investigation.

Carrier capture in quantum well embedded quantum wire structures

We propose a novel quantum wire (QWR) laser structure with improved carrier capture characteristics, where the carriers are injected into a quantum well (QWL) and subsequently recombine within an embedded QWR. The corresponding electron capture rates via polar optical phonon scattering are calculated for this system. An oscillatory behavior of the electron capture rate is observed as a function of the QWR thickness at the temperatures considered (77 K and 300 K). The amplitude of these oscillations also increases as the QWR width decreases. Our calculations show that the electron capture rate in the QWL embedded QWR structure can be improved by more than 30% when compared to single QWLs. Therefore, the proposed QWR laser design provides improved modulation bandwidth and optical gain over conventional QWL and QWR structures.