Guixia Zhu

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.

Monolithic integration of a suspended light-emitting diode with a Y-branch structure

We describe a double-sided process for the monolithic integration of a light-emitting diode (LED) and a Y-branch structure on a GaN-on-silicon platform. The suspended LED and highly confined waveguides are fabricated by silicon removal with back-side thinning of the suspended membrane. When the LED is turned on, part of the light emission is confined by a suspended rectangular waveguide, and the light propagates laterally. The guided light is then coupled into two branching rectangular waveguides and diffracted into the air at the output facets. The light output can be tuned by the LED, opening the potential for more sophisticated integrated photonic circuits.

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 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.

Unidirectional ultraviolet whispering gallery mode lasing from floating asymmetric circle GaN microdisk

Floating asymmetric circle and circle GaN microdisks are fabricated by using standard semiconductor techniques. Unidirectional ultraviolet whispering gallery mode lasing results from floating asymmetric circle GaN microdisks under optical pumping conditions at room temperature. The characteristics of the unidirectional whispering gallery mode lasing, including the lasing emission direction, threshold, emission intensity, and lasing mode number, are studied. A 2D finite difference time domain simulation on optical field distribution confirmed the resonance mechanism of whispering gallery mode lasing. This work is crucial for enhancing collection efficiency and facilitating the coupling of the electronic and photonic devices.

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.