Jingyi Wang

We report on the demonstration of an InGaP/AlGaAs heterojunction avalanche photodiode (APD) with an aluminum composition of 0.8, optimized for high-speed visible-light detection. The APD achieves a 3-dB bandwidth of 2.25 GHz at a multiplication gain of 72, corresponding to a gain–bandwidth product (GBP) of 162 GHz. It exhibits low dark current, low excess noise, and high multiplication gain, highlighting its suitability for high-performance optical applications. To showcase its potential, we integrated the APD into a visible-light communication system with a GaN micro-LED transmitter, achieving a data rate exceeding 1063 Mb/s. These findings highlight the promise of InGaP/AlGaAs APDs for advancing high-speed visible-light communication technologies.

High performance InGaAs photodetectors are highly desired for the ever-growing photoelectric industry. Despite maturity at the production level, the underlying causes of noise and dark current need clarification for further improvement. We studied the dark current and noise characteristics in PIN In0.53Ga0.47As photodiodes with different mesa sizes. The dark current noise exhibits a clear spectral 1/ $f$ shape in all conditions. The results at low temperatures suggest that the dark current is dominated by the sidewall shunt paths while generation-recombination dark current comes into play at high temperatures. The noise intensity follows the squared leakage current in the temperature range of 100-240 K. Since the extracted activation energy of 1/ $f$ noise approximates that of the surface leakage current, suggesting that the surface leakage current may be the primary factor of the 1/ $f$ noise.

Ultra-compact spectrometers are becoming increasingly popular for their promising applications in biomedical analysis, environmental monitoring, and food safety. In this work, we report a single-pixel-photodetector spectrometer with a spectral range from 480 nm to 820 nm, based on the AlGaAs/GaAs p-graded-n junction with a voltage-tunable optical response. To reconstruct the optical spectrum, we propose a tailored method called Neural Spectral Fields (NSF) that leverages the unique wavelength and bias-dependent responsivity matrix. Our spectrometer achieves a high spectral wavelength accuracy of up to 0.30 nm and a spectral resolution of up to 10 nm. Additionally, we demonstrate the high spectral imaging performance of the device. The compatibility of our demonstration with the standard III-V process greatly accelerates the commercialization of miniaturized spectrometers.

In this work, we demonstrate two InGaP/AlGaAs heterojunction avalanche photodiodes with Al component of 0.8 and 0.6 for Li-Fi applications in near-UV and visible light bands. The devices exhibit high multiplication gain, low dark current, and low excess noise factor. By incorporating an InGaP p-layer with a low recombination velocity, we overcome the issue of low UV and near-UV response caused by the high surface recombination of GaAs and AlGaAs materials. The ${Al_{0.8}Ga_{0.2}As}$ device with a recessed window showed an external quantum efficiency (EQE) of 13.12% at 355 nm and 27.12% at 405 nm, with a peak EQE of 38.72% at 440 nm. The ${Al_{0.6}Ga_{0.4}As}$ device exhibits a peak EQE of 43.55% at 540 nm. Furthermore, the photodiodes demonstrate a 3 dB bandwidth of up to 1.59 GHz at 405 nm and 1.12GHz at 520 nm at 99% breakdown voltage. This indicates their future potential for applications in short-distance visible and near-UV light communications.

InGaAs photodiodes have a wide range of important applications; for example, NIR imaging, fiber optical communication, and spectroscopy. In this paper, we studied InGaAs photodiodes with different doping concentration absorber layers. The simulated results suggested that, by reducing the absorber doping concentration from 1 × 10¹⁶ to 1 × 10¹⁵ cm⁻³, the maximum quantum efficiency of the devices can rise by 1.2%, to 58%. The simulation also showed that, by increasing the doping concentration of the absorber layer within a certain range, the dark current of the device can be slightly reduced. A PIN structure was grown and fabricated, and CV measurements suggested a low doping concentration of about 1.2 × 10¹⁵ cm⁻³. Although the thermal activation energy of the dark current suggested a distinct component of shunt dark current at a high temperature range, a dark current of ~6 × 10⁻⁴ A/cm² (−0.5 V) was measured at room temperature. The peak quantum efficiency of the InGaAs device was characterized as 54.7% without antireflection coating and 80.2% with antireflection coating.

Ultra-compact spectrometers are becoming increasingly popular for their promising applications in biomedical analysis, environmental monitoring, and food safety. In this work, we report a novel single-pixel-photodetector spectrometer with a spectral range from 480 nm to 820 nm, based on the AlGaAs/GaAs p-graded-n junction with a voltage-tunable optical response. To reconstruct the optical spectrum, we propose a tailored method called Neural Spectral Fields (NSF) that leverages the unique wavelength and bias-dependent responsivity matrix. Our spectrometer achieves a high spectral wavelength accuracy of up to 0.30 nm and a spectral resolution of up to 10 nm. Additionally, we demonstrate the high spectral imaging performance of the device. The compatibility of our demonstration with the standard III-V process greatly accelerates the commercialization of miniaturized spectrometers.