Single-photon sources are key building blocks in most of the emerging secure telecommunication and quantum information processing schemes. Semiconductor quantum dots (QD) have been proven to be the ...most prospective candidates. However, their practical use in fiber-based quantum communication depends heavily on the possibility of operation in the telecom bands and at temperatures not requiring extensive cryogenic systems. In this paper we present a temperature-dependent study on single QD emission and single-photon emission from metalorganic vapour-phase epitaxy-grown InGaAs/GaAs QDs emitting in the telecom O-band at 1.3 μm. Micro-photoluminescence studies reveal that trapped holes in the vicinity of a QD act as reservoir of carriers that can be exploited to enhance photoluminescence from trion states observed at elevated temperatures up to at least 80 K. The luminescence quenching is mainly related to the promotion of holes to higher states in the valence band and this aspect must be primarily addressed in order to further increase the thermal stability of emission. Photon autocorrelation measurements yield single-photon emission with a purity of Formula: see text up to 50 K. Our results imply that these nanostructures are very promising candidates for single-photon sources at elevated (e.g., Stirling cryocooler compatible) temperatures in the telecom O-band and highlight means for improvements in their performance.
In this study, we propose designs of an interband cascade laser (ICL) active region able to emit in the application-relevant mid infrared (MIR) spectral range and to be grown on an InP substrate. ...This is a long-sought solution as it promises a combination of ICL advantages with mature and cost-effective epitaxial technology of fabricating materials and devices with high structural and optical quality, when compared to standard approaches of growing ICLs on GaSb or InAs substrates. Therefore, we theoretically investigate a family of type II, "W"-shaped quantum wells made of InGaAs/InAs/GaAsSb with different barriers, for a range of compositions assuring the strain levels acceptable from the growth point of view. The calculated band structure within the 8-band k·p approximation showed that the inclusion of a thin InAs layer into such a type II system brings a useful additional tuning knob to tailor the electronic confined states, optical transitions' energy and their intensity. Eventually, it allows achieving the emission wavelengths from below 3 to at least 4.6 μm, while still keeping reasonably high gain when compared to the state-of-the-art ICLs. We demonstrate a good tunability of both the emission wavelength and the optical transitions' oscillator strength, which are competitive with other approaches in the MIR. This is an original solution which has not been demonstrated so far experimentally. Such InP-based interband cascade lasers are of crucial application importance, particularly for the optical gas sensing.
The optical gain spectrum has been investigated theoretically for various designs of active region based on InAs/GaInSb quantum wells-i.e., a type II material system employable in interband cascade ...lasers (ICLs) or optical amplifiers operating in the mid-infrared spectral range. The electronic properties and optical responses have been calculated using the eight-band k·p theory, including strain and external electric fields, to simulate the realistic conditions occurring in operational devices. The results show that intentionally introducing a slight nonuniformity between two subsequent stages of a cascaded device via the properly engineered modification of the type II quantum wells of the active area offers the possibility to significantly broaden the gain function. A-3 dB gain width of 1 µm can be reached in the 3-5 µm range, which is almost an order of magnitude larger than that of any previously reported ICLs. This is a property strongly demanded in many gas-sensing or free-space communication applications, and it opens a way for a new generation of devices in the mid-infrared range, such as broadly tunable single-mode lasers, mode-locked lasers for laser-based spectrometers, and optical amplifiers or superluminescent diodes which do not exist beyond 3 µm yet.
We propose designs for the active region of an interband cascade laser by utilizing a combination of In(As,Sb) and (Ga,In)(As,Sb) materials in a type-II system for strain control and to eventually ...make the entire quantum well lattice-matched to GaSb or InAs substrates. Our k · p modelling results revealed that the tuning ranges for the oscillator strength of the optical transitions and the emission wavelength are beyond what is accessible with the commonly used strained system of InAs/GaInSb. Such a solution, combined with modifications in the passive device sections, can lead to the design and fabrication of a new class of fully unstrained devices operating in the mid-infrared range.
Hereby, we present results of finite-difference time-domain simulations of technologically undemanding photonic structures offering a significant improvement in the spectrally broad extraction ...efficiency of emission from a quantum emitter at the third telecommunication window. The modelling is performed for cylindrical and cuboidal mesa structures containing an exciton confined in a single InAs/InP quantum dot. We investigate the emission pattern from such mesas made of InP (which can be exchanged with AlGaInAs lattice-matched to InP) for two cases: monolithic InP material or InP/AlGaInAs distributed Bragg reflector (DBR) underneath the mesa. The calculations are performed as a function of geometrical parameters, i.e. mesa shape and dimensions, and the emitter position. For the case with DBR, we obtain extraction efficiencies above 25% (for a numerical aperture of 0.4 of a common optical detection system), which also exhibits weak spectral dependence – values above 20% can be obtained in the range of 60 nm around 1550 nm. When the numerical aperture is increased to 0.9, extraction efficiencies about 45% are reachable within the proposed solution. The extraction efficiency is rather weakly sensitive to the in-plane dipole alignment (in the range of 100–200 nm), however, it is more susceptible to even slight changes in its vertical position or to mesa sizes. Eventually, we also comment on the Purcell effect in such weak photonic confinement structures, influence of which on the source brightness is not negligible in some cases.
•Collection of emission from InAs/InP QDs inside photonic structures is modelled.•Extraction efficiency above 45% at 1.55μm for InP-based mesas is obtained.•Spectral independence in the range of above 60nm is demonstrated.•Influence of emission directionality and Purcell effect on brigthness is discussed.
We demonstrate comprehensive numerical studies on a hybrid III-V/Si-based waveguide system, serving as a platform for efficient light coupling between an integrated III-V quantum dot emitter to an ...on-chip quantum photonic integrated circuit defined on a silicon substrate. We propose a platform consisting of a hybrid InP/Si waveguide and an InP-embedded InAs quantum dot, emitting at the telecom C-band near 1550 nm. The platform can be fabricated using existing semiconductor processing technologies. Our numerical studies reveal nearly 87% of the optical field transfer efficiency between geometrically-optimized InP/Si and Si waveguides, considering propagating field along a tapered geometry. The coupling efficiency of a directional dipole emission to the hybrid InP/Si waveguide is evaluated to ∼38%, which results in more than 33% of the total on-chip optical field transfer efficiency from the dipole to the Si waveguide. We also consider the off-chip outcoupling efficiency of the propagating photon field along the Si waveguide by examining the normal to the chip plane and in-plane outcoupling configurations. In the former case, the outcoupling amounts to ∼26% when using the circular Bragg grating outcoupler design. In the latter case, the efficiency reaches up to 8%. Finally, we conclude that the conceptual device's performance is weakly susceptible to the transferred photon wavelength, offering a broadband operation within the 1.5-1.6 µm spectral range.
We present theoretical studies on the confined states in low-strain In(Ga)As quantum dots (QDs). The 8-band k·p model together with the continuum elasticity theory and piezoelectric fields were ...employed to calculate the potential and confined electron and hole eigenstates. We focused on low-indium-content QDs with distinct in-plane asymmetry, which are naturally formed in the low strain regime of the Stranski-Krastanow growth mode. It has been found that the naturally thick wetting layer together with piezoelectric potential affect the total confinement potential to such extent that the hole eigenstates can get the spatial in-plane orientation orthogonal to the main axis of the dot elongation. This can influence both, qualitatively and quantitatively, many of the electronic and optical properties, as e.g. the polarization selection rules for the optical transition or the transitions oscillator strength. Eventually, importance of the degree of the shape asymmetry or the dots’ size, and differences between the low-strain (low-In-content) QDs and pure InAs dots formed in high strain conditions are discussed.
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