Monolithically integrated InAs/InGaAs quantum dot photodetectors on silicon substrates

Breakthrough in Silicon Photonics Technology in Telecommunications, Biosensing, and Gas Sensing

Silicon photonics has been an area of active research and development. Researchers have been working on enhancing the integration density and intricacy of silicon photonic circuits. This involves the development of advanced fabrication techniques and novel designs to enable more functionalities on a single chip, leading to higher performance and more efficient systems. In this review, we aim to provide a brief overview of the recent advancements in silicon photonic devices employed for telecommunication and sensing (biosensing and gas sensing) applications.

Performance optimization of In(Ga)As quantum dot intermediate band solar cells

Quantum dot intermediate band solar cell (QD-IBSC) has high efficiency theoretically. It can absorb photons with energy lower than the bandgap of the semiconductor through the half-filled intermediate band, extending the absorption spectrum of the cell. However, issues in the IBSC, such as the strain around multi-stacking QDs, low thermal excitation energy, and short carrier lifetime, lead to its low conversion efficiency. In recent years, many efforts have been made from different aspects. In this paper, we focus on In(Ga)As QD-IBSC, list the experimental technologies used to improve the performance of the cell and review the recent research progress. By analyzing the effects of different technologies on conversion efficiency, the development direction of the In(Ga)As QD-IBSC in the future is proposed.

A Theoretical Study of Interband Absorption Spectra of Spherical Sector Quantum Dots under the Effect of a Powerful Resonant Laser

We explore the variation of interband absorption spectra of GaAs spherical sector quantum dots (QDs) in response to a strong resonant laser, using the renormalized wave function method. Even though a spherical sector QD appears identical to a section cut from a spherical QD, it contains a controllable additional spatial parameter, the apical angle, which results in radically different wave functions and energy levels of particles, and is anticipated to exhibit novel optical properties. The obtained findings reveal that the apical angle of the dot has a considerable effect on the interband absorption spectrum. With the increase in the dot apical angle, a significant redshift of the interband absorption peaks has been identified. Increasing the pump laser detuning and dot radius yields similar results. Especially when a powerful resonant laser with tiny detuning is utilized, a dynamical coupling between electron levels arises, resulting in the formation of new interband absorption peaks. These new peaks and the former ones were similarly influenced by the aforementioned parameters. Furthermore, it is thought that the new peaks, when stimulated by a suitable laser, will produce the entangled states necessary for quantum information.

C and L band room-temperature continuous-wave InP-based microdisk lasers grown on silicon

Quantum-dot (QD) and quantum-dash (QDash) have been shown to be promising gain materials for lasers directly grown on Si due to their better tolerance to crystal defects and thermal stability. Here we report optically pumped InP-based InAs QDash microdisk lasers (MDLs) directly grown on on-axis (001) Si. To the best of our knowledge, this is the first demonstration of room-temperature continuous-wave lasing of a QDash MDL on Si in the C band and L band. To the best of our knowledge, the lowest threshold of around 400 µW and highest operation temperature of 323 K have been achieved. An analysis of experimental results shows that the dominant lasing wavelength of MDLs varies with the thickness and diameter of the MDLs. Our demonstration shows potential application of MDLs for multi-channel operation in densely integrated Si-photonics.

Photoluminescence of InAs/GaAs quantum dots under direct two-photon excitation

Self-assembled quantum dots grown by molecular beam epitaxy have been a hotbed for various fundamental research and device applications over the past decades. Among them, InAs/GaAs quantum dots have shown great potential for applications in quantum information, quantum computing, infrared photodetection, etc. Though intensively studied, some of the optical nonlinear properties of InAs/GaAs quantum dots, specifically the associated two-photon absorption of the wetting and barrier layers, have not been investigated yet. Here we report a study of the photoluminescence of these dots by using direct two-photon excitation. The quadratic power law dependence of the photoluminescence intensity, together with the ground-state resonant peak of quantum dots appearing in the photoluminescence excitation spectrum, unambiguously confirms the occurrence of the direct two-photon absorption in the dots. A three-level rate equation model is proposed to describe the photogenerated carrier dynamics in the quantum dot-wetting layer-GaAs system. Moreover, higher-order power law dependence of photoluminescence intensity is observed on both the GaAs substrate and the wetting layer by two-photon excitation, which is accounted for by a model involving the third-harmonic generation at the sample interface. Our results open a door for understanding the optical nonlinear effects associated with this fundamentally and technologically important platform.

Ag2S QDs/Si Heterostructure-Based Ultrasensitive SWIR Range Detector

In the 20th century, microelectronics was revolutionized by silicon-its semiconducting properties finally made it possible to reduce the size of electronic components to a few nanometers. The ability to control the semiconducting properties of Si on the nanometer scale promises a breakthrough in the development of Si-based technologies. In this paper, we present the results of our experimental studies of the photovoltaic effect in Ag2S QD/Si heterostructures in the short-wave infrared range. At room temperature, the Ag2S/Si heterostructures offer a noise-equivalent power of 1.1 × 10-10 W/√Hz. The spectral analysis of the photoresponse of the Ag2S/Si heterostructures has made it possible to identify two main mechanisms behind it: the absorption of IR radiation by defects in the crystalline structure of the Ag2S QDs or by quantum QD-induced surface states in Si. This study has demonstrated an effective and low-cost way to create a sensitive room temperature SWIR photodetector which would be compatible with the Si complementary metal oxide semiconductor technology.

Bufferless III-V photodetectors directly grown on (001) silicon-on-insulators

Efficient photodetectors (PDs) and lasers are critical components in silicon photonics technology. Here, we demonstrate bufferless InP/InGaAs PDs, directly grown on (001) silicon-on-insulators. The nano-scale PDs exhibit a high photoresponsivity of 1.06 A/W at 1.55 µm, and a wide operating range from 1450 nm to 1650 nm. The bufferless feature of nano-PDs facilitates effective interfacing with Si waveguides, thus paving the path toward fully integrated silicon photonics circuits.

Low Dark Current 1.55 Micrometer InAs Quantum Dash Waveguide Photodiodes

Photodiodes and integrated optical receivers operating at 1.55 micrometer (μm) wavelength are crucial for long-haul communication and data transfer systems. In this paper, we report C-band InAs quantum dash (Qdash) waveguide photodiodes (PDs) with a record-low dark current of 5 pA, a responsivity of 0.26 A/W at 1.55 μm, and open eye diagrams up to 10 Gb/s. These Qdash-based PDs leverage the same epitaxial layers and processing steps as Qdash lasers and can thus be integrated with laser sources for power monitors or amplifiers for preamplified receivers, manifesting themselves as a promising alternative to their InGaAs and Ge counterparts in low-power optical communication links.

Defect influence on in-plane photocurrent of InAs/InGaAs quantum dot array: long-term electron trapping and Coulomb screening

Metamorphic InAs/In_0.15Ga_0.85As and InAs/In_0.31Ga_0.69As quantum dot (QD) arrays are known to be photosensitive in the telecommunication ranges at 1.3 and 1.55 μm, respectively; however, for photonic applications of these nanostructures, the effect of levels related to defects still needs in-depth investigation. We have focused on the influence of electron traps of defects on photocurrent (PC) in the plane of the QD array, studying by PC and deep level thermally stimulated current spectroscopy together with HRTEM and theoretical modeling. In the structures, a rich spectrum of electron trap levels of point defects EL6 (E _c - 0.37 eV), EL7 (0.29-0.30 eV), EL8 (0.27 eV), EL9/M2 (0.22-0.23 eV), EL10/M1 (0.16 eV), M0 (∼0.11 eV) and three extended defects ED1/EL3 (0.52-0.54), ED2/EL4 (0.47-0.48 eV), ED3/EL5 (0.42-0.43 eV) has been identified. Among them, new defect levels undiscovered earlier in InAs/InGaAs nanostructures has been detected, in particular, EL8 and M0. The found electron traps are shown to affect a time-dependent PC at low temperatures. Besides a long-term kinetics due to trap charging, a prolonged PC decrement versus time is measured under constant illumination. The decrement is interpreted to be related to a Coulomb screening of the conductivity channel by the electrons captured in the QD interface traps. The decrement is well fitted by allometric exponents, which means many types of traps involved in electron capturing. This study provides new findings into the mechanism of in-plane PC of QD arrays, showing a crucial importance of growth-related defects on photoresponsivity at low temperatures.

High-speed photo detection at two-micron-wavelength: technology enablement by GeSn/Ge multiple-quantum-well photodiode on 300 mm Si substrate

We report high-speed photo detection at two-micron-wavelength achieved by a GeSn/Ge multiple-quantum-well (MQW) p-i-n photodiode, exhibiting a 3-dB bandwidth (f3-dB) above 10 GHz for the first time. The epitaxy of device layer stacks was performed on a standard (001)-oriented 300 mm Si substrate by using reduced pressure chemical vapor deposition (RPCVD). The results showed promise for large-scale manufacturing. To our knowledge, this is also the first photodiodes-on-Si with direct radio-frequency (RF) measurement to quantitatively confirm high-speed functionality with tens of GHz f3-dB at 2 µm, which is considered as a promising candidate for the next data communication window. This work illustrates the potential for using GeSn to extend the utility of Si photonics in 2 µm band integrated optical transceivers for communication applications.

Dynamic model and bandwidth characterization of InGaAs/GaAsSb type-II quantum wells PIN photodiodes

In this work, we demonstrated a normal incident PIN InGaAs/GaAsSb type-II multiple quantum wells (MQW) photodiode on InP substrate for 2 μm wavelength high-speed operation. The photodiode has a responsivity of 0.35 A/W at room temperature at 2 μm, and a 3 dB bandwidth of 3.7 GHz. A carrier dynamic model is developed to study the bandwidth of the multiple quantum wells photodiode. Simulation results match the experimental data well, and analysis shows that hole transport limits the 3 dB bandwidth performance. By optimizing the MQW design, higher bandwidth performance (>10 GHz) can be achieved.