Quantum-well Diode Research Articles

Time-division multiplexing wireless light communication network

Owing to emission-detection spectral overlap, a quantum well (QW) diode can detect shorter-wavelength photons emitted from another diode sharing the same QW active region. Therefore, a wireless light communication system can be established by using identical QW diodes that function separately as transmitters and receivers. Here, we investigate the irreversibility between light emission and detection of the QW diode and present a time-division multiplexing (TDM) visible light communication (VLC) network using five identical blue QW diodes that are defined by software as transmitters or receivers to achieve real-time TDM-integrated interconnection via the same optical paths. These results indicate the great potential of realizing an advanced TDM VLC network for diverse applications.

Multiple data streams over a single optical path

Quantum well (QW) diodes have the capability to function as a light-emitting diode or a photodiode and inherently feature a partial emission-detection spectral overlap. Therefore, QW diode can sense light emission from another diode sharing the same QW active region. In association with distributed Bragg reflection (DBR) technique, we here present a wavelength-division multiplexing (WDM) visible light communication (VLC) over a single channel by using vertical assembly of red, green, and blue (RGB) QW diodes. The identical QW diodes separately functioning as a transmitter and a receiver establish a wireless communications link. The DBRs enable the transmission of longer-wavelength photons or the reflection of shorter-wavelength photons, creating an optical bandpass filter in conjunction with emission-detection spectral overlap, effectively boosting the capacity of an initially single communication channel. Both the transmitter and the receiver can be switched freely by software, forming time-division multiplexing (TDM) wireless light communication system using single optical path. We unite TDM and WDM together to demonstrate real-time TDM multichannel bidirectional communication using the vertical integration of RGB QW diodes, offering the great potential to establish TDM-WDM VLC.

Chip-integrated optical fiber force sensing system

The quantum well diode (QWD) performs a dual role, functioning both as an emitter and a detector due to its unique feature of spectral overlap between emission and detection spectra. This dual functionality positions QWDs as promising candidates in the realm of multifunctional sensors. Furthermore, the well-established maturity of optical fiber communication, grounded in its intrinsic property of total reflection, makes it an ideal transmission medium for QWD sensing signals. Leveraging the coexisting emission and detection capabilities of QWDs, we have constructed a sensing system in this article. This system utilizes a QWD, which is stimulated to emit light, with the emitted light traveling through a specified length of optical fiber. A specialized load-bearing film, featuring an aluminum membrane on its rear to act as a mirror and an object of known weight on its front, induces deformation in the film, thereby altering the characteristics of the reflected light. This modulated light is subsequently captured by the QWD via the optical fiber, enabling the computation of the weight of the object. In this article, the QWD's emission peak is around 522 nm, and its detection range extends from 370 to 530 nm. Furthermore, by employing the appropriate approach, integrating QWD with optical fibers can be extended to sensing and measuring various physical quantities such as temperature, solution concentration, wind speed, and more. The advantages of QWDs include cost-effectiveness, multifunctionality, portability, and environmental friendliness. This technology represents a promising avenue for sensor control in the era of the Internet of Things.

Unification of Irreversibility and Energy Diagram Theory.

A simultaneous emission-detection phenomenon occurs when a quantum well (QW) diode is biased with a forward voltage and illuminated with a shorter-wavelength light beam. The diode is able to detect and modulate light emitted by itself due to its spectral emission-detection overlap. Here, two identical QW diode units separately function as a transmitter and a receiver to establish a wireless light communication system. In association with energy diagram theory, we explain the irreversibility between light emission and light excitation in the QW diode, which may help us deeply understand various expressions in nature.

Self-regulation of light emission of an AlGaInP quantum well diode.

When an AlGaInP quantum well (QW) diode is biased with a forward voltage and illuminated with an external shorter-wavelength light beam, the diode is in a superposition state of both light emission and detection. The two different states take place simultaneously, and both the injected current and the generated photocurrent begin to mix. Here, we make use of this intriguing effect and integrate an AlGaInP QW diode with a programmed circuit. The AlGaInP QW diode with the dominant emission peak wavelength centered around 629.5 nm is excited by a 620-nm red-light source. The photocurrent is then extracted as a feedback signal to regulate the light emission of the QW diode in real time without an external or monolithically integrated photodetector, paving a feasible way to autonomously adjust the brightness of the QW diode for intelligent illumination in response to changes in the environmental light condition.

Simultaneous light emission and detection of an AlGaInP quantum well diode

When a quantum well (QW) diode is biased with a forward voltage and illuminated with an external shorter-wavelength light, the device simultaneously emits and detects light, with the injected current and the induced current mixed inside the wells. Separating these superimposed and dynamic electrical signals is useful for the development of multifunctional displays that can simultaneously transmit and receive light signals. By utilizing the unique overlap between the electroluminescence and detection spectra, we establish a wireless optical communication system using two AlGaInP diodes that have identical QW structures. The communication distance is 25 m, with one diode functioning as the transmitter and the other as the receiver. In particular, at the receiver end, the QW diode demonstrates simultaneous light emission and reception ability, and the mixed signals can be efficiently extracted, suggesting great potential for applications from light communication to advanced displays.

Impact of the capture time on power saturation of quantum-well diode lasers

Injected electrons and holes are captured into quantum wells with a non-vanishing time. Simulation results are presented, showing that this results in a non-equilibrium of free and bound carriers in a diode laser. Analysis of an exemplary diode laser structure is used to show that if the capture time is too large, the carrier densities in regions adjacent to the quantum well rise strongly beyond their values at threshold at very high output power. This results in an increase of the free carrier absorption and the non-stimulated recombination, causing a reduction of the slope efficiency and a downwards-bending of the power-current characteristics (power saturation), consistent with experimental results. For the layer structure studied, the additional losses due to accumulation of holes in the n-doped region is predicted to be the dominant effect.

Perspectives on the Development of Metalorganic Vapor Phase Epitaxy for III-V Optoelectronic Devices

The mainstream production of optoelectronic and electronic devices based on epitaxial III-V compound semiconductor materials largely employs metalorganic vapor phase epitaxy, a process first demonstrated for devices in the 1970’s. For this special issue in honor of Prof. P. Daniel Dapkus, this paper first briefly reviews his early contributions that spearheaded the interest of MOVPE as a III-V device epitaxy process. Next, the paper discusses MOVPE reactor development in the 1980’s, which at the time was one of the key challenges in establishing MOVPE technology as a reliable epitaxy manufacturing process. The approach combined physical modeling and numerical simulations of reactor processes followed by materials and device demonstrations. Highly uniform performance metrics of AlGaAs/AlGaAs quantum-well diode lasers and two-dimensional monolithic surface-emitting lasers were demonstrated with excellent run-to-run reproducibility. This foundational approach advanced efforts to standardize reactors and subsequent scaling for high-throughput production.

Compact superluminescent AlGaInAs/InP strain-compensated quantum-well diodes for fibre-optic gyroscopes

Compact superluminescent diodes based on AlGaInAs/InP separate-confinement double heterostructures with strain-compensated quantum wells are studied. The characteristics of these diodes that allow their application for development of fibre-optic gyroscopes in a temperature range from – 55 °C – +70 °C are demonstrated. The devices demonstrate an acceptable reliability and a potential for further improvement.

Wavelength-modulation spectroscopy in the mid-infrared for temperature and HCl measurements in aluminum-lithium composite-propellant flames

This work presents the design, development, and application of a laser-absorption-spectroscopy diagnostic capable of providing quantitative, time-resolved measurements of gas temperature and HCl concentration in flames of metallized composite propellants containing ammonium perchlorate (AP) and hydroxyl-terminated polybutadiene (HTPB). This diagnostic utilizes a quantum-well distributed-feedback diode laser emitting near 3.27 μm to measure the absorbance spectra of HCl using a scanned-wavelength-modulation-spectroscopy technique that is insensitive to non-absorbing transmission losses caused by metal particulates in the flame. This diagnostic was applied to characterize the spatial and temporal evolution of temperature and HCl mole fraction in small-scale flames of AP-HTPB composite propellants containing either an aluminum-lithium alloy or micron-scale aluminum. Experiments were conducted at 1 and 10 atm. At both pressures, the flame temperature of the aluminum-lithium propellant, on a time-averaged basis, was 80 to 200 K higher than that of the aluminum propellant (depending on location in the flame) indicating more complete combustion. In addition, the mole fraction of HCl in the aluminum-lithium propellant flame reached values 65–70% lower than the conventional aluminum-propellant flame at the highest measurement location in the flame. The measurements at both pressures showed similar trends in the reduction of HCl in the aluminum-lithium propellant flame but at elevated pressures this occurred on a length scale nearly an order of magnitude smaller than the flame at atmospheric pressure. The results presented further support that the use of an aluminum-lithium alloy is effective at reducing HCl produced by the propellant flame without compromising performance, thereby making it an attractive additive for solid rocket propellants.

Coexistence of light emission and detection in a III-nitride quantum well diode.

The demand for on-chip multifunctional optoelectronic systems is increasing in today's Internet of Things era. III-nitride quantum well diodes (QWDs) can transmit and receive information through visible light and can be used as both light-emitting diodes (LEDs) and photodetectors (PDs). Spectral emission-detection overlap gives the III-nitride QWD an intriguing capability to detect and modulate light emitted by itself. In this paper, the coexistence of light emission and detection in a III-nitride QWD is experimentally demonstrated, and a wireless video communication system through light is established. When approximately biasing and illuminating at the same time, the III-nitride QWD can achieve light emission and detection simultaneously. This work provides a foundation for the development of multifunctional III-nitride QWDs and the realization of device-to-device data communication.

Experimental Demonstration and Theoretical Analysis of Simultaneous Emission-Detection Phenomenon.

The demand for on-chip multifunctional optoelectronic systems is increasing in the Internet-of-Things era. Spectral emission–detection overlap endows an InGaN/GaN quantum well diode (QWD) with an intriguing capability to detect and modulate light emitted by itself, which is of great interest when merging electronics and photonics together on a single chip for the development of advanced information systems. When biased and illuminated at approximately the same time, the InGaN/GaN QWD can achieve light emission and detection simultaneously. Herein, we experimentally demonstrate the simultaneous emission–detection phenomenon and analyze the irreversibility of spectral emission–detection overlap according to energy diagram theory, which may answer why the QWD can only detect and modulate higher-energy photons than those emitted by itself.

Neutron irradiation effects on gallium nitride-based blue LEDs

Gallium nitride (GaN) is a promising material for radiation-hardened electronics in outer space environment. This work focuses on radiation hardness evaluation of GaN device using commercial GaN quantum-well light-emitting diodes (LEDs). Both the electrical and optical properties of GaN LEDs were characterized before and after neutron irradiation. The light emission intensity was found to increase significantly after 1014n/cm2 of neutron irradiation in the Ohio State University Research Reactor (OSURR) at room temperature. The extracted values from the I-V curve after irradiation also demonstrate such optical improvements of the GaN LED after 1014n/cm2 of neutron irradiation.

Three-Dimensional Modeling of Minority-Carrier Lateral Diffusion Length Including Random Alloy Fluctuations in ( In , Ga ) N and ( Al , Ga ) N Single Quantum Wells

For nitride-based $(\mathrm{In},\mathrm{Ga})\mathrm{N}$ and $(\mathrm{Al},\mathrm{Ga})\mathrm{N}$ quantum-well (QW) light-emitting diodes (LEDs), the potential fluctuations caused by natural alloy disorders limit the lateral intra-QW carrier diffusion length and current spreading. The diffusion length mainly impacts the overall LED efficiency through sidewall nonradiative recombination, especially for $\ensuremath{\mu}\mathrm{LEDs}$. In this paper, we study the carrier lateral diffusion length for nitride-based green, blue, and ultraviolet C (UVC) QWs in three dimensions. We solve the Poisson and drift-diffusion equations in the framework of localization landscape theory. The full three-dimensional model includes the effects of random alloy composition fluctuations and electric fields in the QWs. The dependence of the minority carrier diffusion length on the majority carrier density is studied with a full three-dimensional model. The results show that the diffusion length is limited by the potential fluctuations and the recombination rate, the latter being controlled by the spontaneous and piezoelectric fields in the QWs and by the screening of the internal electric fields by carriers.

Improved performance of InGaN/GaN Near-UV light-emitting diodes with staircase hole injector

We report the enhanced performance of near-ultraviolet (NUV) InGaN/GaN multiple quantum-well (MQW) light-emitting diodes (LEDs) with a staircase hole injector (SHI). Simulation results indicate that the internal electrostatic field in the QW of the LED-SHI is decreased owing to the reduced sheet charge density at the interface between QW and quantum barrier (QB) caused by the smaller In content difference. Additionally, the SHI structure in the QBs suppresses the ballistic or quasi-ballistic hole transport, thus enhancing efficient hole injection into the QWs. The radiative output power of an LED-SHI is increased by 25.3% at 300 mA over that of conventional LEDs with GaN QBs. The droop of internal quantum efficiency (IQE) an LED-SHI at 300 A·cm−1 is 6.1%, while the LED with GaN QBs has an IQE droop of 17.7%. The reduced IQE droop and increased radiative output power in the LED-SHI is attributed to the reduced hole overflow, increased hole injection into the MQW and the decreased electrostatic field in the MQWs. The results show that the SHI structure in the LED is promising for improved performance in high-power GaN-based NUV LEDs.

Impact of the capture time on the series resistance of quantum-well diode lasers

Electrons and holes injected into a semiconductor heterostructure containing quantum wells are captured with a finite time. We show theoretically that this very fact can cause a considerable excess contribution to the series resistivity and this is one of the main limiting factors to higher efficiency for GaAs based high-power lasers. The theory combines a standard microscopic-based model for the capture-escape processes in the quantum well with a drift-diffusion description of current flow outside the quantum well. Simulations of five GaAs-based devices differing in their Al-content reveal the root-cause of the unexpected and until now unexplained increase of the series resistance with decreasing heat sink temperature measured recently. The finite capture time results in resistances in excess of the bulk layer resistances (decreasing with increasing temperature) from 1 mΩ up to 30 mΩ in good agreement with the experiment.

Important role of surface plasmon coupling with the quantum wells in a surface plasmon enhanced color-converting structure of colloidal quantum dots on quantum wells.

To improve the color-conversion efficiency based on a quantum-well (QW) light-emitting diode (LED), a more energy-saving strategy is needed to increase the energy transfer efficiency from the electrical input power of the LED into the emission of over-coated color-converter, not just from LED emission into converted light. In this regard, the efficiency of energy transfer of any mechanism from LED QW into the color-converter is an important issue. By overlaying blue-emitting QW structures and GaN templates with both deposited metal nanoparticles (DMNPs) and color-converting quantum dot (QD) linked synthesized metal nanoparticles (SMNPs) of different localized surface plasmon (LSP) resonance wavelengths for producing multiple surface plasmon (SP) coupling mechanisms with the QW and QD, we study the enhancement variations of their internal quantum efficiencies and photoluminescence decay times. By comparing the QD emission efficiencies between the samples with and without QW, one can observe the advantageous effect of QW coupling with LSP resonances on QD emission efficiency. Also, with the LSP resonance wavelengths of both DMNPs and SMNPs close to the QW emission wavelength for producing strong SP coupling with the QW and hence QD absorption, a higher QD emission or color-conversion efficiency can be obtained.

Bonding stress and reliability of low-polarization quantum-well superluminescent diode

Mechanical stress induced by bonding low-polarization GaAsP/AlGaAs quantum-well superluminescent diodes with p-side-up and p-side-down bonding methods has been observed using measurements of the degree of polarization. Due to the closer distance from the heat-sink to active region and the thermal expansion coefficient mismatch between the oxygen-free copper heat-sink and GaAs-based chip, p-side-down bonding configuration were observed to have a larger stress than p-side-up one. The high temperature accelerated aging test of SLDs with both bonding methods was carried out and discussed. Results suggested that such a bonding stress in superluminescent diode might degrade device's performance, i.e. reducing the threshold level of catastrophic optical damage and improving the failure rate on accelerated aging test.

Extraordinary magnetic field effects mediated by spin-pair interaction and electron mobility in thermally activated delayed fluorescence-based OLEDs with quantum-well structure

We fabricated quantum-well organic light-emitting diodes (QW-OLEDs) based on thermally activated delayed fluorescence (TADF) and measured their magnetic field effects curves over various magnetic field ranges.

Physics of frequency-modulated comb generation in quantum-well diode lasers

Frequency combs are valuable metrological tools that have found several applications in spectroscopy and telecommunications. This work elucidates the physics behind their formation in diode lasers, which may spur further activities on the generation of frequency combs from chip-scale lasers.