InAsP Quantum Wells Research Articles

Low temperature micro-photoluminescence spectroscopy of microstructures with InAsP/InP strained quantum wells

Ridge microstructures were prepared by reactive ion etching (RIE) of a series of stacked InAs x P quantum wells (QWs) with step graded compositions grown on InP by molecular beam epitaxy. These microstructures were characterized by low temperature micro-photoluminescence. The photoluminescence (PL) emission associated with each of the QWs was clearly identified and a model for their line shape was implemented. PL line-scans were measured across etched ridge stripes of various widths in an optical cryostat, with a spatial resolution of 1 µm. The model for the PL spectra allowed accurate extraction of the local PL integrated intensities, spectral positions and line widths. Two different RIE processes, using CH4/H2 and CH4/Cl2, were investigated. The PL line-scans showed strong variations of the integrated PL intensities across the etched stripes. The PL intensities for all QWs increased gradually from the edge to the center of the ridge microstructures, over a length scale of 10–20 µm. On the other hand, the spectral peak position of the PL lines remained constant (within an accuracy of 0.2–0.4 meV, depending on which QW was considered) across the microstructures. These observations are discussed in terms of the mechanical stress induced by the RIE processes, the relaxation of the biaxial built-in compressive stress in the InAsP QWs (induced by the free surfaces at the vertical etched sidewalls), and also by the non-radiative recombination at these sidewalls. Altogether, this study illustrates the contribution that specially designed test structures, coupled with advanced spectroscopic characterization, can provide to the development of semiconductor photonic devices (e.g. lasers or waveguides) involving RIE processing.

Facet-dependent growth of InAsP quantum wells in InP nanowire and nanomembrane arrays

Selective area epitaxy is a powerful growth technique that has been used to produce III-V semiconductor nanowire and nanomembrane arrays for photonic and electronic applications. The incorporation of a heterostructure such as quantum wells (QWs) brings new functionality and further broadens their applications. Using InP nanowires and nanomembranes as templates, we investigate the growth of InAsP QWs on these pure wurtzite nanostructures. InAsP QWs grow both axially and laterally on the nanowires and nanomembranes, forming a zinc blende phase axially and wurtzite phase on the sidewalls. On the non-polar {11[combining macron]00} sidewalls, the radial QW selectively grows on one sidewall which is located at the semi-polar 〈112[combining macron]〉 A side of the axial QW, causing the shape evolution of the nanowires from hexagonal to triangular cross section. For nanomembranes with {11[combining macron]00} sidewalls, the radial QW grows asymmetrically on the {11[combining macron]00} facet, destroying their symmetry. In comparison, nanomembranes with {112[combining macron]0} sidewalls are shown to be an ideal template for the growth of InAsP QWs, thanks to the uniform QW formation. These QWs emit strongly in the near IR region at room temperature and their emission can be tuned by changing their thickness or composition. These findings enrich our understanding of the QW growth, which provides new insights for heterostructure design in other III-V nanostructures.

Effect of postgrowth heat treatment on the structural and optical properties of InP/InAsP/InP nanowires

The effect of the postgrowth annealing of InP/InAsP/InP heterostructural nanowires produced by molecular-beam epitaxy on their structural and optical properties is studied. It is shown that the procedure of short-term (1 min) annealing in an argon atmosphere provides a means for increasing the emission intensity of InAsP quantum dots, suppressing the emission from InAsP quantum wells formed as a result of lateral growth, and substantially reducing the density of structural defects in the nanowires.

Ultra-low threshold polariton lasing in photonic crystal cavities

The authors show clear experimental evidence of lasing of exciton polaritons confined in L3 photonic crystal cavities. The samples are based on an InP membrane in air containing five InAsP quantum wells. Polariton lasing is observed with thresholds as low as 120 nW, below the Mott transition, while conventional photon lasing is observed for a pumping power one to three orders of magnitude higher.

Two-dimensional surface emitting photonic crystal laser with hybrid triangular-graphite structure

We present laser emission of a compact surface-emitting micro laser, optical pumped and operating at 1.5 microm at room temperature. A two-dimensional photonic crystal lattice conformed in a hybrid triangular-graphite configuration is designed for vertical emission. The structures have been fabricated in an InP slab, including four InAsP quantum wells as active layer, on the top of a Si substrate SiO(2) wafer bonded. Laser emission with thresholds around 70 microW and quality factors (Qs) up to 12000 have been measured. The Bloch mode selected for the emission keeps a high Q (>or= 2 x 10(5)) around the Gamma point for a wide range of in-plane values k(||) <or= 0.1(2 pi/a) which is related to peculiar properties of the hybrid lattice.

Effect of implementation of a Bragg reflector in the photonic band structure of the Suzuki-phase photonic crystal lattice

We investigate the change of the photonic band structure of the Suzuki-phase photonic crystal lattice when the horizontal mirror symmetry is broken by an underlying Bragg reflector. The structure consists of an InP photonic crystal slab including four InAsP quantum wells, a SiO(2) bonding layer, and a bottom high index contrast Si/SiO(2) Bragg mirror deposited on a Si wafer. Angle- and polarization-resolved photoluminescence spectroscopy has been used for measuring the photonic band structure and for investigating the coupling to a polarized plane wave in the far field. A drastic change in the k-space photonic dispersion between the structure with and without Bragg reflector is measured. An important enhancement on the photoluminescence emission up to seven times has been obtained for a nearly flat photonic band, which is characteristic of the Suzuki-phase lattice.

Surface-emitting microlaser combining two-dimensional photonic crystal membrane and vertical Bragg mirror

We report on the design and fabrication of heterogeneous and compact surface-emitting microlasers, optically pumped and operating at 1.5μm at room-temperature. A very low threshold, below 15μW, is achieved. The devices consists of a top two-dimensional InP photonic crystal slab, including four InAsP quantum wells, a SiO2 bonding layer, and a bottom high index contrast Si∕SiO2 Bragg mirror deposited on a Si wafer. The graphitelike photonic crystal lattice is tailored for vertical emission. We theoretically and experimentally demonstrate that the Bragg reflector can strongly enhance the quality factor of the photonic crystal resonant mode, leading to a drastic decrease of the lasing threshold.

Heterogeneous integration of electrically driven microdisk based laser sources for optical interconnects and photonic ICs

A new approach for an electrically driven microlaser based on a microdisk transferred onto Silicon is proposed. The structure is based on a quaternary InGaAsP p-i-n junction including three InAsP quantum wells, on a thin membrane transferred onto silicon by molecular bonding. A p++/n++ tunnel junction is used as the p-type contact. The technological procedure is described and first experimental results show a laser emission in pulsed regime at room temperature, with a threshold current near 1.5 mA.

Influence of compressive strain on the arsenic incorporation in MOVPE-grown InAsP/InP single quantum wells

In this paper we have studied the effect of MOVPE growth conditions on the arsenic incorporation in strained InAsP quantum wells (QWs) grown on InP substrates. Lower growth temperatures result in an enhanced arsenic incorporation, as well as an improvement in the quality of the heterostructure. It is seen that an increase in the arsine flux does not readily increase the arsenic composition in the film which is dependent on temperature, strain and growth conditions.

Conduction-Band Discontinuity of InAsP/InP Heterojunction

The band line-up of InAsP/InP heterojunctions was investigated. The conduction-band discontinuity ratio Qc of strained InAsP alloys was determined by fitting the well thickness dependence of transition energies in InAsP quantum wells. This method does not require precise values of deformation potentials of InAsP, allowing more reliable determination of the band offset. The obtained Qc value was 0.35, which is relatively small compared to previous reports. This value of the band offset is consistent with the predictions from the semi-empirical linear combination of atomic orbitals (LCAO) model.

InAsP/InGaAsP periodic gain structure for 1.5 μm vertical cavity surface emitting laser applications

We have studied the capabilities of chemical beam epitaxy (CBE) to produce high-gain media for long-wavelength (1.5 μm) vertical cavity surface emitting lasers (VCSELs). Using a parameter pair of low growth temperature and small V/III ratio the integration of up to 15 highly strained (1.78%) InAsP quantum wells (QWs) into a periodic gain structure (PGS) is successfully demonstrated. In this work we present data of atomic force microscopy (AFM), X-ray diffraction, reflectivity and electro-luminescence measurements that prove the very good structural and optical quality of this CBE grown PGS. As an alternative to conventional multi quantum well (MQW) systems as active layers, a high-performance PGS may be used in a VCSEL structure to reduce the very strict requirements on the InP-based distributed Bragg reflectors (DBRs) or to increase the achievable output power. Due to the use of thickness-reduced InP-based DBRs in conjunction with a PGS as the active region the fabrication of fully epitaxial grown long-wavelength VCSELs might also be possible with CBE.

Low threshold 1.55 μm wavelength InAsP/InGaAsP strained multiquantum well laser diode grown by chemical beam epitaxy

By using chemical beam epitaxy at growth temperatures as low as 460–480 °C, we have overcome strain relaxation problems that prevented so far the successful use of InAsP quantum wells in 1.55 μm lasers. Five quantum well InAsP/InGaAsP horizontal cavity lasers showed 88% internal efficiency, 1.6 cm−1 losses per well, and 33 A/cm2 transparency current density per well, which equal or even surpass the best published characteristics for 1.55 μm wavelength lasers based on any material system. Moreover, up to 17 quantum wells were integrated in a strain-balanced laser, which showed equally good characteristics.

Strain and relaxation effects in InAsP/InP multiple quantum well optical modulator devices grown by metal-organic vapor phase epitaxy

Strained-layer multiple quantum well (MQW) InAsP/InP optical modulators have been fabricated from layers grown by metal-organic vapor phase epitaxy. The devices are a series of p-i(MQW)-n photodiodes in which the active core regions consist nominally of 25 periods of 10 nm InAsP quantum wells of 4.4%, 10.0%, 15.6%, and 26.4% As composition separated by 10 nm InP barriers. Structural parameters for the samples were obtained using high-resolution x-ray diffraction rocking curves and transmission electron microscopy. The series contains samples with both coherently strained and partially relaxed multi-layers where the relaxation is characterized by misfit dislocations. The band offsets for the heterostructures were determined by fitting the energy positions of the optical absorption peaks with those computed using the Marzin–Bastard model for strained-layer superlattices [as in M. Beaudoin et al., Phys. Rev. B 53, 1990 (1996)]. The conduction band discontinuities thus obtained are linear in the As composition (7.56±0.08 meV per As % in the InAsP layer) at low and room temperature for As concentrations up to 39%, and up to 17% average relaxation. Comparisons between the coherently strained and partially relaxed samples demonstrated a broadening of optical transition linewidths due to relaxation which appears to be of minor consequence for optical modulator devices as the essential optical and electrical properties remain intact. The electric field-dependent red-shift of the n=1 electron-heavy hole transition was measured by a photocurrent method and found to be enhanced in structures with lower barrier heights.