Yongchao Yang

On-chip integration of suspended InGaN/GaN multiple-quantum-well devices with versatile functionalities.

We propose, fabricate and demonstrate on-chip photonic integration of suspended InGaN/GaN multiple quantum wells (MQWs) devices on the GaN-on-silicon platform. Both silicon removal and back wafer etching are conducted to obtain membrane-type devices, and suspended waveguides are used for the connection between p-n junction InGaN/GaN MQWs devices. As an in-plane data transmission system, the middle p-n junction InGaN/GaN MQWs device is used as a light emitting diode (LED) to deliver signals by modulating the intensity of the emitted light, and the other two devices act as photodetectors (PDs) to sense the light guided by the suspended waveguide and convert the photons into electrons, achieving 1 × 2 in-plane information transmission via visible light. Correspondingly, the three devices can function as independent PDs to realize multiple receivers for free space visible light communication. Further, the on-chip photonic platform can be used as an active electro-optical sensing system when the middle device acts as a PD and the other two devices serve as LEDs. The experimental results show that the auxiliary LED sources can enhance the amplitude of the induced photocurrent.

On-chip photonic system using suspended p-n junction InGaN/GaN multiple quantum wells device and multiple waveguides

We propose, fabricate, and characterize the on-chip integration of suspended p-n junction InGaN/GaN multiple quantum wells(MQWs) device and multiple waveguides on the same GaN-on-silicon platform. The integrated devices are fabricated via a wafer-level process and exhibit selectable functionalities for diverse applications. As the suspended p-n junction InGaN/GaN MQWs device operates under a light emitting diode(LED) mode, part of the light emission is confined and guided by the suspended waveguides. The in-plane propagation along the suspended waveguides is measured by a micro-transmittance setup. The on-chip data transmission is demonstrated for the proof-of-concept photonic integration. As the suspended p-n junction InGaN/GaN MQWs device operates under photodiode mode, the light is illuminated on the suspended waveguides with the aid of the micro-transmittance setup and, thus, coupled into the suspended waveguides. The guided light is finally sensed by the photodiode, and the induced photocurrent trace shows a distinct on/off switching performance. These experimental results indicate that the on-chip photonic integration is promising for the development of sophisticated integrated photonic circuits in the visible wavelength region.

Integrated p–n junction InGaN/GaN multiple-quantum-well devices with diverse functionalities

We propose, fabricate, and demonstrate integrated p–n junction InGaN/GaN multiple-quantum-well devices with diverse functionalities on a GaN-on-silicon platform. Suspended devices with a common n-contact are realized using a wafer-level process. For the integrated devices, part of the light emitted by a light-emitting diode (LED) is guided in-plane through a suspended waveguide and is sensed by another photodiode. The induced photocurrent is tuned by the LED. The integrated devices can act as two independent LEDs to deliver different signals simultaneously for free-space visible light communication. Furthermore, the suspended devices can be used as two separate photodiodes to detect incident light with a distinct on/off switching performance.

Simultaneous light emission and detection of InGaN/GaN multiple quantum well diodes for in-plane visible light communication

Abstract This paper presents the design, fabrication, and experimental characterization of monolithically integrated p-n junction InGaN/GaN multiple quantum well diodes (MQWDs) and suspended waveguides. Suspended MQWDs can be used as transmitters and receivers simultaneously, and suspended waveguides are used for light coupling to create an in-plane visible light communication system. Compared to the waveguide with separation trench, the calculated total light efficiency is increased from 18% to 22% for the continuous waveguide. The MQWDs are characterized by their typical current-voltage performance, and the pulse excitation measurements confirm that the InGaN/GaN MQWDs can achieve the light emission and photodetection at the same time. The photocurrent measurements indicate that the photocurrent is modulated by a bias voltage and that the photons are being supplied from another transmitter. An experimental demonstration is presented showing that the proposed device works well for in-plane full-duplex communication using visible light.

Saturation Behavior for a Comb-Like Light-Induced Synaptic Transistor

We propose and fabricate a comb-like light-induced synaptic transistor composed of two InGaN/GaN multiple-quantum-well diodes (MQWDs) with a common base. One InGaN/GaN MQWD is used as an emitter of light, and another InGaN/GaN MQWD is used as a collector. When a presynaptic voltage is applied to the emitter to generate light, the collector absorbs the emitted light and demonstrates an excitatory postsynaptic voltage (EPSV). Saturated EPSV behavior occurs at the collector when multiple pulse signals are continuously applied to the emitter. The saturated EPSV value is increased and the saturated pulse number is reduced as the amplitude of the applied pulse signal increases. Experimental results indicate that continuous stimuli with a high pulse intensity will greatly improve the memory effect during the learning process.

Light Induced Synaptic Transistor With Dual Operation Modes

We propose and fabricate a light induced transistor using a combination of two multiple-quantum-well diodes (MQWDs) with a common n-electrode as the base. Both silicon removal and back wafer etching are conducted to obtain a suspended device architecture. The InGaN/GaN MQWD detects light only when the bias voltage is below the turn-ON voltage and can simultaneously achieve light emission and detection when it turns ON. Therefore, the light induced transistor operates with two distinct light detection modes. The excitatory postsynaptic voltages (EPSVs) are distinct due to the different decay times. Paired-pulse facilitation is experimentally demonstrated to mimic the synaptic plasticity behavior. The EPSV amplitudes are dependent on the pulse interval and pulse number.

On-chip integration for in-plane video transmission using visible light

We demonstrate a wafer-level process for achieving monolithic photonic integration of a light-emitting diode (LED) with a waveguide and photodiode on a GaN-on-silicon platform. Both silicon removal and back-side thinning are conducted to achieve a suspended device architecture. A highly confined waveguide that utilizes the large index contrast between GaN and air is used for the connection between the LED and the photodiode. The suspended waveguide is considered as an in-plane escape cone of the LED, and the photodiode is located at the other end of the waveguide. The photons emitted from the LED are transported to the photodiode through the suspended waveguide parallel to the LED surface, leading to in-plane data transport using visible light. This proof-of-concept monolithic integration paves the way towards in-plane visible light communication as well as photonic computation on a single chip.

On-chip optical interconnect using visible light

We propose and fabricate a monolithic optical interconnect on a GaN-on-silicon platform using a wafer-level technique. Because the InGaN/GaN multiple-quantum-well diodes (MQWDs) can achieve light emission and detection simultaneously, the emitter and collector sharing identical MQW structure are produced using the same process. Suspended waveguides interconnect the emitter with the collector to form in-plane light coupling. Monolithic optical interconnect chip integrates the emitter, waveguide, base, and collector into a multi-component system with a common base. Output states superposition and 1×2 in-plane light communication are experimentally demonstrated. The proposed monolithic optical interconnect opens a promising way toward the diverse applications from in-plane visible light communication to light-induced artificial synaptic devices, intelligent display, on-chip imaging, and optical sensing.

Mirco Signal Wireless-Communication Device Based on GaN-on-Silicon Platform with Light Emitting Diodes

In this paper, we demonstrate a photonic wireless-communication device based on GaN-on-silicon platform with membrane light emitting diodes for in-plane ultra-short distance visible light communication (VLC). We utilize two bidirectional InGaN/GaN multiple-quantum-well devices integrated on one chip as signal emitter and receiver, which are operated under light-emitting diode (LED) or photo detector (PD) mode respectively. The peak wavelength 450nm in electroluminescent (EL) spectra is applicable for blue range. As a micro-scale device, it can be operated on higher frequency above 30MHz and the optimum frequency is from 30MHz to 90MHz. The light with direct modulation carrying digital signal is detected by PD and has excellent transmit performance at 50Mbps rate with low inter-symbol interference (ISI). In particular, the integrated device has the lowest bit error rate (BER) at 80MHz bandwidth. The stable transmit frequency and communication rate could be applied for small clients such as smart phone and so on. For further study, the improved rate with better performance will let the client maintain the 4G even the 4G + transmission rate for a long term.

Suspended waveguide photodetector featuring p-n junction InGaN/GaN multiple quantum wells

In this paper, we report on the fabrication and characterization of a suspended waveguide photodetector featuring p-n junction InGaN/GaN multiple quantum wells (MQWs) on a GaN-on-silicon platform. Both silicon removal and back wafer etching are conducted to achieve the suspended waveguide photodetector combination. The light illumination measurements experimentally demonstrate that the metallization stacks can serve as the bottom metal mirror to reflect the incoming light back for re-absorption, leading to an improved photocurrent response. The out-of-plane light can couple into the suspended waveguide and propagate as a confined optical mode, resulting in an induced photocurrent. The photodetector exhibits two operation modes. The peak values of the responsivity spectra for the suspended waveguide photodetector are located around 401 nm at 3 V bias and 435 nm at 0 V bias, respectively. These results pave a promising way to develop the suspended waveguide photodetector for diverse applications in the visible wavelength region.