Resonant-cavity Light-emitting Diodes Research Articles

Integrated sensor chip of a resonant cavity light emitter and photon detector for wearable optical medicine

This work presents an integrated chip of a resonant cavity light emitter and photon detector (RCLEPD) to address the requirements of wearable optical medical devices for compact size, high efficiency, and interference resistance sensors. The optical radiation pattern and light extraction efficiency of the resonant cavity light emitting diode (RCLED) as well as the optical absorption spectrum of the resonant cavity enhanced photon detector (RCEPD) are theoretically simulated. Additionally, the wavelength selectivity of the RCEPD absorption spectrum is analyzed. Material epitaxial growth of RCLEPD was performed using metal-organic chemical vapor deposition (MOCVD), and an integrated sensing chip with an area of 2 × 2 mm2 was fabricated. Experimental results demonstrate that RCLED achieves a maximum external quantum efficiency of 10.206%, consistent with the simulation results, while maintaining a peak wavelength at 677.5 nm within a current range of 0-20 mA. Furthermore, the RCEPD exhibits a peak response wavelength at 678 nm, matching that of the RCLED. Utilizing RCLEPD as the sensor, photoplethysmography (PPG) signals are collected from the human wrist under different RCLED driving currents resulting in an average period of 977 ms which aligns with a human pulse frequency of 61 beats/min. With further processing techniques applied to PPG signals, RCLEPD is expected to be used as a sensor in wearable blood pressure and glucose monitoring devices.

High Q Factor and High Power Density Ultraviolet Resonant-Cavity Light-Emitting Diodes

High Q Factor and High Power Density Ultraviolet Resonant-Cavity Light-Emitting Diodes

Ultraviolet-B Resonant-Cavity Light-Emitting Diodes with Tunnel Junctions and Dielectric Mirrors.

We demonstrate the first electrically injected AlGaN-based ultraviolet-B resonant-cavity light-emitting diode (RCLED). The devices feature dielectric SiO2/HfO2 distributed Bragg reflectors enabled by tunnel junctions (TJs) for lateral current spreading. A highly doped n++-AlGaN/n++-GaN/p++-AlGaN TJ and a top n-AlGaN current spreading layer are used as transparent contacts, resulting in a good current spreading up to an active region mesa diameter of 120 μm. To access the N-face side of the device, the substrate is removed by electrochemically etching a sacrificial n-AlGaN layer, leading to a smooth underetched surface without evident parasitic etching in the n- and n++-doped layers of the device. The RCLEDs show a narrow emission spectrum with a full width at half-maximum (FWHM) of 4.3 nm compared to 9.4 nm for an ordinary LED and a more directional emission pattern with an angular FWHM of 52° for the resonance at 310 nm in comparison to ∼126° for an LED. Additionally, the RCLEDs show a much more stable emission spectrum with temperature with a red-shift of the electroluminescence peak of about ∼18 pm/K and a negligible change of the FWHM compared to LEDs, which shift ∼30 pm/K and show spectrum broadening with temperature. The demonstration of those devices, where a highly reflective mirror is spatially separated from an ohmic metal contact, opens up a new design space to potentially increase the poor light extraction efficiency in UV LEDs and is an important step toward electrically injected UV vertical-cavity surface-emitting lasers.

GaN-based resonant-cavity light-emitting diode towards a vertical-cavity surface-emitting laser

GaN-based resonant-cavity light-emitting diode towards a vertical-cavity surface-emitting laser

Resonant cavity enhanced InAs/GaAsSb SLS LEDs with a narrow spectral linewidth and a high-spectral intensity operating at 4.6 μm

We investigated the design, growth, fabrication, and characterization of InAs/GaAsSb SLS resonant cavity light emitting diodes (RCLEDs) grown on InAs by molecular beam epitaxy. The structure consists of a 1λ-thick micro-cavity positioned between two lattice-matched AlAsSb/GaAsSb distributed Bragg reflector mirrors (DBRs). A 44-pair InAs/GaAsSb SLS active region is placed at the antinode of the electric field intensity in the center of the cavity. Electroluminescence emission spectra were recorded at room-temperature. Due to the resonant cavity effect, 400 μm-diameter SLS RCLEDs exhibited emission spectra peaked at 4.587 μm with a narrow spectral linewidth of 52 nm. A high-spectral intensity of >3 mW cm−2 nm−1 was achieved for the 400 μm SLS RCLED using 1% duty cycle to avoid Joule heating. Furthermore, temperature dependence of the emission spectra of the RCLED showed excellent temperature stability, with a rate of 0.34 nm/K. Compared to existing mid-infrared 5-stage InAs/GaAsSb SLS ICLEDs operating at ∼4.5 μm, the (400 μm-diameter) InAs/GaAsSb SLS RCLEDs exhibited 10.5× brighter spectral intensity, 14× narrower spectral linewidth, and 8× improvement in the temperature stability. Owing to these attractive features, our SLS RCLEDs could be used to develop the next generation CO gas instruments and active imaging.

GaN-on-Si micro resonant-cavity light-emitting diodes with dielectric and metal mirrors

Micro-LED is a new type of display technology. Its advantages are high resolution, high brightness, long life, low power consumption and so on. However, due to the reduction in size, the proportion of surface damage increases, resulting in a decrease in device performance, which affects the development of Micro-LEDs. In this paper, ion implantation technology and resonant cavity structure are used to reduce device sidewall damage and improve device characteristics. The photoelectric properties of GaN-based blue micro light emitting resonant cavity diodes were studied. Pixel-to-pixel isolation is achieved by fluorine ion implantation. The resonant cavity structure is fabricated by wafer bonding technique. The research shows that the electrical characteristics of the device have realized good stability. Under medium reflectivity conditions, the device enhancement effect is best when the reflectivity of the top mirror is 40%. With the decrease of the size, the enhancement of optical characteristics weakens due to the size effect, and the spontaneous emission intensity of the 10 μm device increases by 212.6%. The FWHM of devices with different sizes narrowed by about 10 nm. The stability of the device peak wavelength and full width at half maximum is improved. Therefore, this paper provides research value for the application of resonant cavity structures in Micro-LEDs.

Cavity Mode-Matching InGaN Aperture-Emitting Device with a Nanoporous GaN Reflector via Ion Implantation

Cavity mode-matching InGaN resonant-cavity light-emitting diodes (RC-LEDs) with aperture size-dependent emission have been demonstrated through nitrogen ion (N+) implantation and electrochemical wet etching processes. The RC-LED structure consisted of 570 nm-depth ion-implanted regions and an embedded 17-pair nanoporous-GaN/n-GaN distributed Bragg reflector (DBR) outside the aperture, while there existed a full 20-pair DBR structure within the aperture regions. Shorter and mode-matching cavity lengths were fabricated, confirmed by transmission electron microscopy and angle-resolved photoluminescence spectra inside the aperture area without subjecting to the N+ implantation. By reducing the aperture sizes, higher current density and narrower far-field electroluminescence emission patterns were observed in the RC-LED with an aperture size of 40 μm-diameter. These results demonstrate that the cavity mode-matching RC-LEDs with optical/electrical confinements and controllable cavity length mismatch features can be applied in a wide range of optoelectronic-based device applications.

GeSn/Ge Multiquantum-Well Vertical-Cavity Surface-Emitting p-i-n Structures and Diode Emitters on a 200 mm Ge-on-Insulator Platform

An efficient monolithically integrated light source with complementary metal-oxide-semiconductor (CMOS) compatibility remains the missing component to enable Si photonics for various applications. In particular, vertical-cavity-surface-emitting (VCSE) light sources, such as resonant cavity light-emitting diodes (RCLEDs) and vertical-cavity surface-emitting lasers (VCSELs), are strong contenders due to their compact size, circular emission profile with low beam divergence, wafer-scale fabrication compatibility, high bandwidth, and high coupling efficiency to fiber optic cables. We report the first demonstration of 8-in. wafer-scale GeSn/Ge multiple-quantum-well VCSE p-i-n structures and diodes for laser or light-emitting diode (LED) applications in Si photonics by wafer bonding and layer transfer techniques, which are challenging for all-epitaxy routes. The wafer could be 12 in. (300 mm) since the MQW gain medium is grown on a 300 mm Si wafer, and the bonding is wafer-scale. Alternative dielectric layers (SiO2/SiN/SiO2), introduced by wafer bonding, under the emitting structure, serve as the bottom mirror for the vertical cavity. The Ge0.92Sn0.08/Ge MQW layer is utilized to improve the material quality and to confine injected carriers. As a result, more than 8× enhancement of light emission due to the vertical cavity resonance was demonstrated by photoluminescence spectroscopy. Besides, the spectral purity is enhanced by the single-longitudinal-mode cavity. The intensity of light emission is insensitive to the temperature range from 4 to 300 K and even becomes stronger at higher temperatures since the stronger resonant cavity effect at higher temperatures compensates for the drop in light emission efficiency caused by nonradiative centers. The vertical cavity effect on the light emission is further verified by reflectivity spectroscopy and optical simulations. A positive gain can be achieved as indicated by optical gain calculations. Room-temperature electroluminescence and an excellent carrier injection efficiency of the MQW VCSE diode are observed, showing its potential for electrically injected RCLEDs and VCSELs.

Plasmonic biosensor with annular aperture array integrated on a resonant cavity LED

In this paper, we propose an intensity-sensitive compact plasmonic sensor by integrating an annular aperture array with a resonant cavity LED (RCLED). The extraordinary optical transmission (EOT) peak originates from the mutual coupling between surface plasmon polariton (SPP) and Localized surface plasmon resonance (LSPR), which utilizes the EOT peak with narrower linewidth for intensity modulation. Simulation results show that by optimizing the resonant wavelength of the annular aperture array to match the emission wavelength of the RCLEDs, the relative intensity change reaches 97%, and the intensity sensitivity is 9744 %/RIU as a protein molecular layer covered on the sensor.

Ultraviolet-C AlGaN Resonant-Cavity Light-Emitting Diodes with Thermal Stability Pipe-AlGaN-Distributed Bragg Reflectors.

Ultraviolet-C AlGaN resonant-cavity light-emitting diodes with top and bottom pipe-AlGaN-distributed Bragg reflectors (DBRs) have been demonstrated. For the top/bottom DBR structures, 20 pairs of n+-AlGaN:Si/n-AlGaN:Si stack structures were transformed into the pipe-AlGaN:Si/n-AlGaN:Si DBRs through a doping-selective electrochemical wet etching process. The reflectivity of the pipe-AlGaN DBR structure was measured as 90% at 276.7 nm with a 20.9 nm flat stopband width. The anisotropic optical properties of the pipe-AlGaN DBR structure had been analyzed through the polarization-dependent reflectance spectra. For temperature-dependent reflectance spectra, the central wavelengths were slightly redshifted from 275 nm (100 K) to 281 nm (600 K) due to thermal expansion, refractive index increase, and partial strain release phenomena in the pipe-DBR structure. High photoluminescence emission intensity and line-width reducing phenomena were observed at 10 K in the UVC-LED with the resonant-cavity structure, which has potential for high-efficiency UV-C light source applications.

Mid-infrared resonant light emission from GeSn resonant-cavity surface-emitting LEDs with a lateral p-i-n structure

We demonstrate room-temperature, mid-infrared resonant electroluminescence from GeSn resonant-cavity LEDs with a lateral p-i-n configuration on a silicon-on-insulator substrate. A vertical cavity to enhance light emission in the GeSn active layer is formed by the low-index buried oxide and deposited SiO 2 layer. A planar lateral p-i-n diode structure favorable for CMOS-compatible, dense integration was designed and fabricated for current injection. Under continuous-wave electrical injection, room-temperature resonant electroluminescence was successfully observed at ∼ 1980 nm with a spectral emission factor of 2.2. These results could pave the way toward efficient electrically injected GeSn light emitters operating at room temperature.

Gallium nitride-based resonant cavity light-emitting diode with single-longitudinal-mode emission.

A novel, to the best of our knowledge, gallium nitride (GaN)-based resonant cavity light-emitting diode (RCLED) with single-longitudinal-mode light emission was demonstrated. A Ta2O5/SiO2 dielectric distributed Bragg reflector (DBR) with a filter-film structure was adopted as the top mirror. In contrast to the flat-topped reflectivity spectrum of the conventional high-reflective-structure DBR, for this filter-film-structure DBR, there is a light-transmitting concave band on the reflectivity spectrum. Owing to the modulation effect of this band on the output light, a single-longitudinal-mode light emission with a full width at half maximum as low as 0.63 nm was realized. Furthermore, the novel RCLED exhibited better wavelength stability. With an increase in the injection current from 50 to 500 mA, the redshift of the emission peak was only 0.2 nm. This novel RCLED with ultra-narrowband emission has a high potential for application in optical communication systems and optical fiber sensing applications.

InGaN-Based Orange-Red Resonant Cavity Light-Emitting Diodes

InGaN-based orange-red resonant cavity light-emitting diodes (RCLEDs), were fabricated by using an AlN current-confinement aperture and double dielectric distributed Bragg reflectors (DBRs). For realizing the structure of device, a substrate transfer technique was employed in process of fabrication. The device exhibited optical resonant effect, a high Q factor (∼3010), and a narrow emission linewidth (FMHW ∼0.2 nm), indicating low optical loss in the resonant cavity. Additionally, due to the three-dimensional (3D) optical confinement effect, the discrete modes of red emission were clearly observed in the far field via an angular resolved measurement system. And then, the energies of the photon states of a red RCLED consists generally with the simulation results based on a circular waveguide model. The saturated emission intensity of the orange-red RCLED was proportional to the area of current injection. This work demonstrated the feasibility of InGaN-based electrically injected orange-red RCLEDs that are useful for the development of displays and communication systems.

GaN-based green resonant-cavity light-emitting diodes with Al mirror and copper plate.

In this Letter, GaN-based green resonant-cavity light-emitting diodes (RCLEDs) with a low-cost aluminum (Al) metal bottom mirror, a dielectric top mirror, and a copper (Cu) supporting plate were fabricated. The green-emitting epitaxial wafer was grown on a patterned sapphire substrate (PSS) to ensure high crystal quality (CQ). Laser lift-off (LLO) of the PSS and electrical plating of a Cu supporting plate were then carried out to realize the vertical device structure. The emission wavelength and full width at half maximum (FWHM) of the main emission peak of the device are ∼518 nm and 14 nm, respectively. Under the current density of 50 A/cm2, a relatively high light output power (LOP) of 11.1 mW can be obtained from the green RCLED. Moreover, when the current injection is 20 mA (8 A/cm2), the corresponding forward bias voltage is as low as ∼2.46 V. The reasons for the low operating voltage and high LOP can be attributed to the improvement of CQ, the release of residual compressive stress of the GaN-based epilayer due to the removal of PSS, and better heat dissipation properties of the Cu supporting plate.

Influence of top mirror on performance of GaN-based resonant cavity light-emitting diode

In this paper, two kinds of distributed Bragg reflectors (DBRs) with high-reflective-film structure and filter structure are designed and evaporated on the top of GaN-based resonant cavity light emitting diode (RCLED), respectively. Firstly, the reflectivity spectra of the two kinds of DBRs are simulated. Then, the differences in performance including optical longitudinal modes, spectral linewidth, and output light intensity between the two kinds of RCLED devices with different top mirrors, are compared and analyzed. Finally, the influence of the top mirror reflection characteristics on the output spectrum of the RCLED is studied in detail. The results show that the top mirror is an important part of RCLED, and its reflection characteristics determine the optical performance of the device. For the conventional DBR with high-reflective-film structure, its reflectivity spectrum has a wide high-reflection band. Accordingly, the spectral linewidth of the RCLED can be effectively narrowed by using the conventional DBR as the top mirror. However, the spectrum still consists of multi-longitudinal modes. For the DBR with filter structure, its reflectivity spectrum has a narrow high-transmittance band at the central wavelength. Depending on the modulation effect of the high-transmittance band to the output light, single longitudinal mode light emission is realized for the RCLED with the specially designed DBR as the top mirror, which shows a broad application prospect in optical communication and optical fiber sensing. Moreover, the spectral characteristics of the RCLED can be further optimized to meet its application requirements in much more fields, by designing the top mirror structure and changing its reflectivity spectrum characteristics.

GaN-Based Resonant-Cavity Light-Emitting Diodes Grown on Si.

GaN-on-Si resonant-cavity light-emitting diodes (RCLEDs) have been successfully fabricated through wafer bonding and Si substrate removal. By combining the chemical mechanical polishing technique, we obtained a roughness of about 0.24 nm for a scan area of 5 μm × 5 μm. The double-sided dielectric distributed Bragg reflectors could form a high-quality optical resonant cavity, and the cavity modes exhibited a linewidth of 1 nm at the peak wavelength of around 405 nm, corresponding to a quality factor of 405. High data transmission in free space with an opening in the eye diagram was exhibited at 150 Mbps, which is limited by the detection system. These results showed that GaN-based RCLEDs grown on Si are promising as a low-cost emitter for visible light communications in future.

Improving the Modulation Bandwidth of GaN‐Based Light‐Emitting Diodes for High‐Speed Visible Light Communication: Countermeasures and Challenges

Visible light communication (VLC) has attracted widespread attention for wireless communications. The popularity of GaN‐based light‐emitting diodes (LEDs) has also laid a solid foundation for the application of VLC. As the light source of VLC, LED's modulation bandwidth directly determines the speed of communication. Herein, reviewing progress on modulation bandwidth improvement schemes of GaN LEDs transmitter is reviewed, covering aspects from epitaxial to devices. Epitaxial approaches include c‐polar facet epitaxial optimization, non/semipolar facet epitaxial growth, and chip scheme such as micro‐LEDs, nano‐LEDs, resonant cavity‐LEDs (RC‐LEDs), plasmon, and metacavity LEDs. In terms of white LEDs, approaches to tackle the slow Stokes transfer and long carrier life for conventional phosphors including new color‐conversion materials (CCMs) and new energy transfer routes are reviewed. This review promotes the development of GaN‐based LEDs as the transmitter for high‐speed VLC.

Study on the effect of top mirror on the performance of GaN-based resonant cavity light-emitting diode

本文在GaN基共振腔发光二极管（RCLED）顶部设计制备了高反膜结构分布式布拉格反射镜（DBR）和滤波器结构DBR两种反射镜，对比分析了两种反射镜的反射率曲线特征以及对应的RCLED器件的光输出纵模模式、光谱线宽和输出光强等性能差异，详细研究了顶部反射镜的光反射特性对RCLED器件输出光谱性能的影响机理。研究结果表明，顶部反射镜是RCLED的重要组成部分，其反射率曲线特征决定器件的光输出性能。常规高反膜结构DBR顶部反射镜的反射率曲线具有较宽的高反射带，将其作为顶部反射镜可有效压窄RCLED发光纵模线宽，但是发光光谱仍呈现多纵模光输出特征。滤波器结构DBR顶部反射镜的反射率曲线在中心波长处具有较窄的透光凹带，利用透光凹带对输出光的调制作用，器件可实现单纵模光输出，在光通信、光纤传感等领域展示了广阔的应用前景。通过进一步设计RCLED顶部反射镜结构，可以改变其反射率曲线特性，进而优化RCLED器件的输出光谱特性，以满足器件在多个领域的应用需求。

Research progress in the epitaxial growth of silicon-based group IV materials, and their light emitters and photodetectors

Silicon-based optoelectronic integrated circuits, which are composed of silicon-based light sources, photodetectors, light modulators, and other modules, are core technologies in the recent information era. Silicon is the cornerstone of microelectronic integration, but it encounters issues with optoelectronic integration. First, as an indirect bandgap material, silicon is difficult to be used in high-efficiency light sources, which is still currently the biggest challenge. Second, the absorption coefficient of silicon in the near-infrared communication band is very low, so it is not suitable for the near-infrared photodetectors. Silicon-compatible group IV materials can achieve direct band through band engineering. They have a high absorption coefficient in the near-infrared and have attracted extensive attention of researchers. In this paper, the research progress of epitaxial growth of silicon-based materials, and their light emitters and photodetectors, are reviewed. The growth technologies of Ge, SiGe/Ge heterojunction, quantum wells, and GeSn quantum dots are introduced. Based on the above silicon-based group IV heterostructure materials, a new method for modulating the height of the contact barrier between metal and semiconductor was proposed. Also, various photodetectors with different structures were developed. The lateral heterojunction LED and vertical resonant-cavity LED, including dual active regions compatible with traditional CMOS processes, were developed. The luminescence performance of the devices was improved effectively and the luminescence gain of strain Ge was observed.

InGaN Resonant-Cavity Light-Emitting Diodes with Porous and Dielectric Reflectors

InGaN based resonant-cavity light-emitting diode (RC-LED) structures with an embedded porous-GaN/n-GaN distributed Bragg reflector (DBR) and a top dielectric Ta2O5/SiO2 DBR were demonstrated. GaN:Si epitaxial layers with high Si-doping concentration (n+-GaN:Si) in the 20-period n+-GaN/n-GaN stacked structure were transformed into a porous-GaN/n-GaN DBR structure through the doping-selective electrochemical wet etching process. The central wavelength and reflectivity were measured to be 434.3 nm and 98.5% for the porous DBR and to be 421.3 nm and 98.1% for the dielectric DBR. The effective 1λ cavity length at 432nm in the InGaN resonant-cavity consisted of a 30 nm-thick Ta2O5 spacer and a 148 nm-thick InGaN active layer that was analyzed from the angle-resolved photoluminescence (PL) spectra. In the optical pumping PL spectra, non-linear emission intensity and linewidths reducing effect, from 6.5 nm to 0.7 nm, were observed by varying the laser pumping power. Directional emission pattern and narrow linewidth were observed in the InGaN active layer with bottom porous DBR, top dielectric DBR, and the optimum spacer layer to match the short cavity structure.