InGaAs QW Research Articles

Radial Growth Evolution of InGaAs/InP Multi-Quantum-Well Nanowires Grown by Selective-Area Metal Organic Vapor-Phase Epitaxy.

III-V semiconductor multi-quantum-well nanowires (MQW NWs) via selective-area epitaxy (SAE) is of great importance for the development of nanoscale light-emitting devices for applications such as optical communication, silicon photonics, and quantum computing. To achieve highly efficient light-emitting devices, not only the high-quality materials but also a deep understanding of their growth mechanisms and material properties (structural, optical, and electrical) are extremely critical. In particular, the three-dimensional growth mechanism of MQWs embedded in a NW structure by SAE is expected to be different from that of those grown in a planar structure or with a catalyst and has not yet been thoroughly investigated. In this work, we reveal a distinctive radial growth evolution of InGaAs/InP MQW NWs grown by the SAE metal organic vapor-phase epitaxy (MOVPE) technique. We observe the formation of zinc blende (ZB) QW discs induced by the axial InGaAs QW growth on the wurtzite (WZ) base-InP NW and propose it as the key factor driving the overall structure of radial growth. The role of the ZB-to-WZ change in the driving of the overall growth evolution is supported by a growth formalism, taking into account the formation-energy difference between different facets. Despite a polytypic crystal structure with mixed ZB and WZ phases across the MQW region, the NWs exhibit high uniformity and desirable QW spatial layout with bright room-temperature photoluminescence at an optical communication wavelength of ∼1.3 μm, which is promising for the future development of high-efficiency light-emitting devices.

Effect of low and staggered gap quantum wells inserted in GaAs tunnel junctions

In this article, we investigate the impact of the insertion of either a type I InGaAs or a type II InGaAs/GaAsSb quantum well on the performances of MBE-grown GaAs tunnel junctions (TJs). The devices are designed and simulated using a quantum transport model based on the non-equilibrium Green’s function formalism and a 6-band k.p Hamiltonian. We experimentally observe significant improvements of the peak tunneling current density on both heterostructures with a 460-fold increase for a moderately doped GaAs TJ when the InGaAs QW is inserted at the junction interface, and a 3-fold improvement on a highly doped GaAs TJ integrating a type II InGaAs/GaAsSb QW. Thus, the simple insertion of staggered band lineup heterostructures enables us to reach a tunneling current well above the kA cm−2 range, equivalent to the best achieved results for Si-doped GaAs TJs, implying very interesting potential for TJ-based components, such as multi-junction solar cells, vertical cavity surface emitting lasers and tunnel-field effect transistors.

Comparative study on stained InGaAs quantum wells for high-speed optical-interconnect VCSELs

The gain-carrier characteristics of InGaAs quantum well for 980 nm high-speed, energy-efficient vertical-cavity surface-emitting lasers are investigated. We specially studied the potentially InGaAs quantum well designs can be used for the active region of energy-efficient, temperature-stable 980-nm VCSEL, which introduced a quantum well gain peak wavelength-to-cavity resonance wavelength offset to improve the dynamic performance at high operation temperature. Several candidate quantum wells are being compared in theory and measurement. We found that ∼5 nm InGaAs QW with ∼6 nm barrier thickness is suitable for the active region of high-speed optical interconnect 980 nm VCSELs, and no significant improvement in the 20% range of In content of InGaAs QWs. The results are useful for next generation green photonic device design.

Novel type II InGaAs/GaAsBi quantum well for longer wavelength emission

We propose a new type II InGaAs/GaAsBi quantum well structure to extend light emission wavelength on GaAs and demonstrate the effect experimentally. Type II InGaAs/GaAsBi QWs were grown using molecular beam epitaxy. Room temperature photoluminescence confirms wavelength extension to 1230 nm, 82 and 208 nm longer than that of the type I GaAsBi and InGaAs QW with the same Bi or In content, respectively. The PL intensity is enhanced by more than ten times than the GaAsBi QW. Our results show that the type II dilute bismide QW has potentials for making telecom lasers on GaAs.

Growth of laser diode structures with emission wavelength beyond 1100 nm for yellow–green emission by frequency conversion

Laser structures for emission wavelengths of 1120nm and 1180nm, suitable for non-linear frequency conversion to yellow–green and yellow–orange, were developed. At 1120nm emission wavelength different active regions and structures were investigated. The introduction of a GaAs spacer layer between GaAsP barriers and InGaAs QWs reduces threshold and transparency current density significantly. Lifetime measurements were done successfully over 1700h for broad area and 10000h for ridge waveguide tapered lasers.Broad area laser diodes with a partly strain-compensated 6nm InGaAs QW, emitting at 1180nm, show lifetimes above 1000h at an output power of 1.5W. The required beam quality was achieved by processing a ridge waveguide laser with an included distributed Bragg reflector. Such a laser emits up to 200mW in single mode output power.

Crystallographic dependent in-situ CBr4 selective nano-area etching and local regrowth of InP/InGaAs by MOVPE

Selective area etching and growth in the metalorganic vapor phase epitaxy (MOVPE) reactor on nano-scale structures have been examined. Using different mask orientations, crystallographic dependent etching of InP can be observed when carbon tetrabromide (CBr4) is used as an etchant. Scanning Electron Microscopy (SEM) investigation of etch profiles showed formation of a U-shaped groove along the [01̄1̄] direction, terminated by {111}B planes with an ~15nm {100} plateau and transitional {311}B planes, developed in a self-limiting manner. In the perpendicular direction [01̄1] etching with a dominant lateral component driven by fast etched {111}A and {311}A side planes was observed. A directly grown single InGaAs QW in the etched grooves demonstrated different QW profiles: a crescent-shaped on {311}B and {100} planes (along the [01̄1̄] direction) and two separated quarter-circle curvatures grown preferably on {311}A along [01̄1̄]. Room temperature micro-photoluminescence measurements indicated a wavelength red-shift in over 125nm along [01̄1̄] comparing to [01̄1], which is related to both growth enhancement and composition variation of the grown material.

InGaAs circular-grating-coupled surface emitting laser with focusing function fabricated by electron beam writing with circular scanning

We report the design, fabrication and operation of an InGaAs QW circular-grating-coupled surface emitting laser (CGCSEL) which can focus the output laser beam. Circular distributed Bragg reflector and circular chirped grating coupler were fabricated by electron beam lithography employing smooth circular scanning and two step reactive ion etching. Single-mode-like lasing at a wavelength of 978.3 nm was accomplished. Focusing function was confirmed and the focused spot size around 80 μm was obtained.

Effect of growth temperature and quantum structure on InAs/GaAs quantum dot solar cell.

InGaAs-capped InAs quantum dots (QDs) and InAs QDs were adopted for the study of the effects through growth temperature and the band structure of InAs QDs on the performance of GaAs-based QD solar cell. It has been shown that the defects due to low temperature growth resulted in the decrease of Voc, Jsc and external quantum efficiency for GaAs bulk solar cell and QD embedded solar cells. It has been also found that InAs QDs act as defects by trapping photo-generated carries which affect the carrier transport in QD solar cell. The QD solar cell with InGaAs-capped InAs QDs showed higher performance than the QD solar cell with only InAs QDs. Such result has been explained by photo-generated carrier trapping and tunneling through InGaAs QW state in InGaAs-capped InAs QDs.

Optical and Magnetic Properties of Ten-Period InGaMnAs/GaAs Quantum Wells

Ten layers of InGaMnAs/GaAs multiquantum wells (MQWs) structure were grown on high resistivity (100) p-type GaAs substrates by molecular beam epitaxy (MBE). A presence of the ferromagnetic structure was confirmed in the InGaMnAs/GaAs MQWs structure, and have ferromagnetic ordering with a Curie temperature, T C=50 K. It is likely that the ferromagnetic exchange coupling of the sample with T C=50 K is hole-mediated resulting in Mn substituting In or Ga sites. PL emission spectra of the InGaMnAs MQWs sample grown at a temperature of 170 °C show that an activation energy of the Mn ion on the first quantum confinement level in InGaAs QW is 32 meV and impurity Mn is partly ionized. The fact that the activation energy of 32 meV of Mn ion in the QW is lower than an activation energy of 110 meV for a substitutional Mn impurity in GaAs, indicating an impurity band existing in the bandgap due to substitutional Mn ions.

LT-InGaAs Layer Grown for Near Surface SESAM Application

We have developed a mode-locked diode-pumped Yb:KYW laser generating nearly band-width limited pulses as short as 101 fs using semiconductor saturable absorber mirror (SESAM). With the nonsaturable losses of 1.94% and the modulation depth of 1.48% the self-starting and stable mode-locking was observed. The nonsaturable losses are mainly related to AsGa-CB transitions in InGaAs QW absorbing layer and low temperature defects. Low temperature defects are eliminated by using higher growth temperature and lower ratio of group V to group III beam equivalent pressure than typically used. The InGaAs layer was grown by molecular beam epitaxy at the temperature as high as 420 ◦C, under the V/III ratio as low as 10. No annealing was performed.

Electroluminescence from modulation-doped pseudomorphic AlGaAs/InGaAs/GaAs quantum wells

Low-temperature electroluminescence (EL) is observed in n-type modulation-doped AlGaAs/InGaAs/GaAs quantum well samples by applying a positive voltage between the semitransparent Au gate and alloyed Au–Ge Ohmic contacts made on the top surface of the samples. We attribute impact ionization in the InGaAs QW to the observed EL from the samples. A redshift in the EL spectra is observed with increasing gate bias. The observed redshift in the EL spectra is attributed to the band gap renormalization due to many-body effects and quantum-confined Stark effect.

Optimization of the highly strained InGaAs/GaAs quantum well lasers grown by MOVPE

In this article, we study the highly compressive-strained InGaAs/GaAs quantum wells and the broad-area lasers grown by MOVPE. Several epitaxial parameters were optimized, including the growth temperature, pressure and group V to group III (V/III) ratio. Grown with the optimized epitaxial parameters, the highly strained In 0.39Ga 0.61As/GaAs lasers could be continuously operated at 1.22 μm and their threshold current density Jth was 140 A/cm 2. To the best of our knowledge, the demonstrated InGaAs QW laser has the lowest threshold current per quantum well (Jth/QW) of 46.7 A/cm 2. The fitted characteristic temperature ( T 0) was 146.2 K, indicating the good electron confinement ability. Furthermore, by lowering the growth temperature down to 475 °C and the TBAs/III ratio to 5, the emission wavelength of the In 0.42Ga 0.58As/GaAs quantum wells was as long as 1245 nm and FWHM was 43 meV.

Short exciton radiative lifetime in submonolayer InGaAs∕GaAs quantum dots

The exciton radiative lifetime in submonolayer (SML) InGaAs∕GaAs quantum dots (QDs) grown at 500°C was measured by using time-resolved photoluminescence from 10to260K. The radiative lifetime is around 90ps and is independent of temperature below 50K. The observed short radiative lifetime is a key reason for the high performance of SML QD devices and can be explained by the theory of Andreani et al. [Phys. Rev. B 60, 13276 (1999)] calculating the radiative lifetime of QDs formed at the interface fluctuations of a quantum well, as the SML QDs are 20–30nm in diameter and embedded within the lateral InGaAs QW.

Highly efficient InGaAs QW vertical external cavity surface emitting lasers emitting at 1060 nm

We report on the high-power operation of an optically pumped VECSEL emitting at 1060 nm. The VECSEL structure, grown by MOVPE, consists of resonant periodic gains and 35 pairs of AlAs/AlGaAs DBR. A single In 0.28GaAs quantum well is positioned at each antinode of the optical standing wave. The VECSEL chip is water-bonded by capillarity to a diamond heatspreader. 10 W continuous wave operation is achieved with an optical-to-optical conversion efficiency of 44% at room temperature. High efficiency and good thermal stability are mainly due to the optimization of epitaxial quality and the high conductivity of the diamond heatspreader. We have found that the increase of the round trip caused by the heat spreader is about 1%.

High-efficiency InGaAs QW distributed Bragg reflector laser with curved grating for squeezed light generation

A high-efficiency InGaAs quantum-well curved distributed Bragg reflector (DBR) laser was designed for squeezed light generation and fabricated using a selective-area quantum-well disordering technique to reduce absorption loss in the DBR grating region. Single-mode lasing with side-mode suppression ratio of 50 dB was obtained, and an external differential quantum efficiency as high as 0.71 was achieved under continuous-wave operation. Using balanced detection technique, the laser intensity noise relative to the standard quantum limit (SQL) was measured. Ultra-low noise characteristic of 0.8 dB below the standard quantum limit was achieved by wideband constant-current driving of the laser. This is the first demonstration of single-mode squeezed light generation by a monolithic semiconductor laser at room temperature.

Room-Temperature Preperation of InGaAsN Quantum Dot Lasers Grown by MOCVD

An InGaAsN single-layer quantum dot ~QD! laser structure was grown on GaAs substrates by metalorganic chemical vapor deposition ~MOCVD!. The ridge-waveguide edge emitting laser diodes ~LD! were fabricated and characterized. We demonstrate room-temperature operation of InGaAsN QD lasers with an emission wavelength of 1078 nm. Electroluminescence spectra as a function of injection current showed that InGaAsN QD LDs lased from an excited QD state at room temperature. The evidence for QD-related absorption was obtained from the comparison of photocurrent spectra between a reference InGaAs QW and the InGaAsN QD structures.

Design of two-dimensional photonic-crystal mirrors for InGaAs QW laser applications

We report on the design of highly reflecting two-dimensional photonic crystal (2D-PC) mirrors, which can be integrated in a short InGaAs QWs laser source, operating around 970 nm. These mirrors consist of a triangular lattice of air holes into the GaAs slab, whose geometrical parameters have been calculated by the effective index method and 2D plane wave expansion method. A 2D finite-difference time-domain (2D-FDTD) model has also been used in order to evaluate the transmission and reflection characteristics of 2D-PC front and back mirrors of the in-plane laser. Finally, a detailed description of the nanotechnology processes necessary for the fabrication of ultra-compact in-plane laser is shown.

Design of two-dimensional photonic-crystal mirrors for InGaAs QW laser applications

We report on the design of highly reflecting two-dimensional photonic crystal (2D-PC) mirrors, which can be integrated in a short InGaAs QWs laser source, operating around 970 nm. These mirrors consist of a triangular lattice of air holes into the GaAs slab, whose geometrical parameters have been calculated by the effective index method and 2D plane wave expansion method. A 2D finite-difference time-domain (2D-FDTD) model has also been used in order to evaluate the transmission and reflection characteristics of 2D-PC front and back mirrors of the in-plane laser. Finally, a detailed description of the nanotechnology processes necessary for the fabrication of ultra-compact in-plane laser is shown.

Annealing effect on the optical properties in Si delta-doped Al 0.24Ga 0.76As/In 0.15Ga 0.85As/GaAs pseudomorphic high electron mobility transistor structures

The optical properties of Si delta-doped Al 0.24Ga 0.76As/In 0.15Ga 0.85As/GaAs pseudomorphic high electron mobility transistor structure (PHEMTs) are estimated after the process of rapid thermal annealing (RTA) in the temperature range 500–750°C. After layer intermixing and decrease of 2DEG densities of PHEMTs just occurs around the annealing temperature of 650°C, the 12H transition peak at 1.354 eV above the annealing temperature of 650°C is newly observed from the photoluminescence (PL) and photoreflectance (PR) spectra. From the results of PL and PR measurements in the annealed PHEMTs, it is found that remarkable modification of band profile in InGaAs QW occur at annealing temperature above 650°C.

Excitonic binding in coupled quantum wells

We study excitonic states in the presence of applied electric field in 8-nm GaAs coupled quantum wells (QW's) separated by a 4-nm ${\mathrm{Al}}_{0.33}{\mathrm{Ga}}_{0.67}\mathrm{As}$ barrier and in 6-nm ${\mathrm{In}}_{0.1}{\mathrm{Ga}}_{0.9}\mathrm{As}$ coupled QW's separated by a 4-nm GaAs barrier in which effects attributed to macroscopically ordered excitonic states have been recently reported. We discuss the differences in the nature of the states and in the origin of confinement which determines the change of excitonic properties with increase in the applied electric field in both structures. We have found that the indirect exciton binding energy for the field amplitude used in the experiment with InGaAs QW's is around 3.5 meV, much less than the previously reported 10 meV value. This suggests that the optically induced ring structure, reported to persist to near 100 K, might not be caused by collective excitonic transport.