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In this study, we propose and simulate the design of a non-regrowth staircase channel GaN vertical trench transistor, demonstrating an exceptional threshold and breakdown characteristic for high power and high frequency applications. The unique staircase design provides a variable capacitance through the gate-dielectric-semiconductor interface, which results in a high breakdown voltage of 1.52 kV and maintains a channel on-resistance of 2.61 mΩ∙cm2. Because of the variable length and doping profile in the channel region, this model offers greater flexibility to meet a wide range of device application requirements.

Surface plasmon resonance (SPR) has emerged as one of the most efficient and attractive techniques for optical sensors in biological applications. The traditional approach of an EC (electrochemical)-SPR biosensor to generate SPR is by adopting a prism underneath the sensing substrate, and an angular scan is performed to characterize the reflectivity of target analytes. In this paper, we designed and investigated a novel optical biosensor based on a hybrid plasmonic and electrochemical phenomenon. The SPR was generated from a thin layer of gold nanohole array on a glass substrate. Using C-Reactive Protein (CRP) as the target analyte, we tested our device for different concentrations and observed the optical response under various voltage bias conditions. We observed that SPR response is concentration-dependent and can be modulated by varying DC voltages or AC bias frequencies. For CRP concentrations ranging from 1 to 1000 µg/mL, at the applied voltage of -600 mV, we obtained a limit of detection for this device of 16.5 ng/mL at the resonance peak wavelength of 690 nm. The phenomenon is due to spatial re-distribution of electron concentration at the metal-solution interface. The results suggest that CRP concentration can be determined from the SPR peak wavelength shift by scanning the voltages. The proposed new sensor structure is permissible for various future optoelectronic integration for plasmonic and electrochemical sensing.

Traditional methods of monitoring biochemical reactions measure certain detectable reagents or products while assuming that the undetectable species follow the stoichiometry of the reactions. Here, based upon the metal-oxide thin-film transistor (TFT) biosensor, we develop a real-time molecular diffusion model to benchmark the concentration of the reagents and products. Using the nicotinamide adenine dinucleotide (NADH)-oxaloacetic acid with the enzyme of malate dehydrogenase as an example, mixtures of different reagent concentrations were characterized to extract the ratio of remaining concentrations between NAD+ and NADH. We can thus obtain the apparent equilibrium constant of the reaction, (8.06 ± 0.61) × 104. Because the whole analysis was conducted using a TFT sensor fabricated using a semiconductor process, our approach has the advantages of exploring biochemical reaction kinetics in a massively parallel manner.

The dynamic on-resistance increase during power switching is one of the challenges of GaN-based HEMTs (high-electron-mobility transistors) for power electronic applications. Both the surface traps and buffer traps reduce channel carriers, resulting in decreased operating current during power switching. In this work, we propose a source metal trench toward the buffer region to alleviate channel carriers’ trapping in the buffer region. We compare the dynamic behaviors of the HEMTs with the source trench fabricated within and out of the mesa region. The results indicate less dynamic on-resistance increase at higher drain and gate stress voltages of the device with source trench in the mesa, as compared with the device with source trench fabricated away from mesa, or the one without a trench. We further develop physical models, including multiple current-conducting paths, reduction of buffer traps through source trench, and the re-distribution of the electric field profile, to explain the phenomenon.

Understanding the binding affinities and kinetics of protein-ligand interactions using a label-free method is crucial for identifying therapeutic candidates in clinical diagnostics and drug development. In this work, the IGZO-TFT (thin-film transistor) biosensor integrated with a tailored microfluidic chip was developed to explore binding kinetics of protein-ligand biochemical interactions in the real-time manner. The IGZO-TFT sensor extracts the binding characteristics through sensing biomolecules by their electrical charges. Using lysozyme and tri-N-acetyl-D-glucosamine (NAG3) as an example, we established a procedure to obtain the parameters, such as the dissociation constant, Kd, and association rate constant, ka, that are critical to biochemical reactions. The correlation between the lysozyme concentration and TFT drain current signal was first constructed. Next, solutions of lysozyme and NAG3 of different mixing ratios were prepared. They were pre-mixed for various periods of reaction time before applying to the TFT sensor to extract signals of lysozyme molecules and the concentration remaining. With the knowledge of drain current changes at different reaction times, ka and Kd can be obtained. The values from our experiment are comparable to other methods, which suggests the proposed approach can be employed to explore protein-ligand interaction kinetics in the massively parallel manner if the TFT array is considered.

The decrease of light output efficiency with the reduction of LED (light-emitting diode) die size is one of the challenges of micro-LED displays. Here we propose a digital etching technology that employs multi-step etching and treatment to mitigate sidewall defects exposed after mesa dry etching. In this study, by two-step etching and N2 treatment, the electrical properties of the diodes show an increase of forward current and a decrease in reverse leakage due to suppressed sidewall defects. An increase of light output power by 92.6% is observed for 10 × 10-µm2 mesa size with digital etching, as compared with that with only one step etching and no treatment. We also demonstrated only 1.1% decrease in output power density for a 10 × 10-µm2 LED as compared with a 100 × 100-µm2 device without performing digital etching.

Traditional visible light communication (VLC) via light-emitting diodes (LEDs) employs the on-off keying (OOK) modulation scheme. Even though optical frequency modulation has many advantages, it is hardly used for LED VLC because a high carrier frequency cannot be applied to the LED cavity due to the resistance-capacitance limit. Here, by monolithically integrating an LED with an integrated digital transducer, we experimentally demonstrate the intermixing of gigahertz surface acoustic waves and electrical data signals in the LED cavity at room temperature. An optical transmitter was realized by in situ frequency up-conversion of the data signals from an LED, which has the advantages of improving transmission performance by up-shifting the data spectrum away from low-frequency noise. Our proposed integrated acousto-optic transducer opens a new developing scheme on the frequency up-mixed data encoding of an LED beyond its inherent modulation bandwidth for future VLC.

The fundamental detection scheme of typical grating or photonic crystal (PhC) sensors relies on the correlation of the diffraction behaviors with the refractive index of target analyte. For biomaterial detection, a thin gold film is usually deposited on the sensor surface so that cross linkers can be anchored before functionalizing the device. The nanoscale metallic film suggests plasmonic resonances play a critical role in light-matter interaction. In this work, we demonstrated a compact two-dimensional (2D) hexagonal PhC biosensor with thin gold film coating. In such a device, surface plasmon polariton (SPP) on the metal structure and phase matching of optical wave with the PhC are considered when analyzing light-biomaterial interaction on the detector. Using Epstein-Barr nuclear antigen-1 (EBNA-1) antibody as an example, protein sensing along different lattice orientations of the PhC biosensor was investigated. Based on the dispersion relationship and phase matching conditions, we unravel the mechanisms involved in the wavelength shifts and sensitivities. The simulation results verify the phenomenon of tighter spatial confinement and higher local field intensity from the SPP, which helps detecting small variations of the refractive index on the sensor surface.

We experimentally study the effect of amplitude-varying surface acoustic waves on a localized surface plasmon (LSP), which unveils exceptional properties of plasmon-phonon interaction with promising applications in future tunable photonic devices. Gold nanoparticles are deposited on X-cut LiNbO 3 to generate plasmonic oscillation, and an interdigital transducer is fabricated to create surface acoustic wave pulses. The interaction between an amplitude-varying mechanical wave and a plasmonic oscillation affects different plasmon dynamics and relaxation gradients, leading to a systematic change in LSP absorption. We also demonstrated the effect of polarized light on the device, providing a unique characteristic to explore the manipulation process effectively.

Though the acoustoelectric and acoustooptic interactions have been widely studied on III–V semiconductors, most studies were conducted at low temperature to avoid the influence of lattice scattering. Here, we demonstrate larger-than-1-GHz optical oscillation and acoustic charge transport at room temperature from a nitride-based LED (light-emitting diode) by acoustic wave excitation. The optical oscillation is generated by the harmonics of acoustic waves, while the acoustic transport of carriers was observed from the LED light output at different acoustic excitation frequencies. Furthermore, with the change of bias voltage, the frequency response of light output varies correspondingly due to the thermal disturbance that affects the lattice vibration and acoustic wave propagation. The results also suggest that we are able to achieve a tunable optical resonant frequency by varying bias voltages without changing the LED structure.

We propose GaN based LEDs with the photonic crystal structure for VLC applications with a bit rate up to 400Mb/s using on-off keying modulation and orthogonal frequency division multiplexing transmission capacity up to 2 Gbit/s.

Optomechanical properties have been widely explored on the interactions between phonon, photon, and electrons. The applications range from acoustic filters for mobile handsets to quantum information science./However, up to date, the interaction between harmonic modes of surface acoustic waves (SAWs) and photons has not been studied in detail. Here, we develop radio frequency (RF) - modulated light emitters driven by the coupling between electrical and acoustic signals at room temperature. The light emitter demonstrates a 990-MHz oscillation behavior which cannot be solely achieved by electrical driving due to resistance–capacitance ( RC ) limit. Instead, the result is attributed to the excitation by the harmonics of SAWs in the light emitter. The ~gigahertz light oscillation enables a new architecture for information processing. In this work, we also demonstrate the coupling between acoustooptical and electrooptical interactions by simultaneously applying 990-MHz acoustic signals and 20-MHz modulated electrical inputs.

Recently, GaN-based light-emitting diodes (LEDs) find their applications in, other than general lighting, visible light communication (VLC) for high-speed wireless data networks. The pursuit for more bandwidth from the LED can be realized by engineering the LED material structure and device design, or by modulation techniques. In this paper, we proposed GaN-based LEDs with the photonic crystal (PhC) structure for VLC applications. Contradictory to general thought that higher small frequency response translates to better large-signal performance, our results reveal that a PhC LED may not perform well at low data rate due to its relatively poorer signal-to-noise ratio (SNR). However, at higher data rates, the performance of PhC LEDs surpasses conventional LED structure. We showed data transmission capability of PhC LEDs with a bit rate up to 400 Mb/s using on–off keying modulation. To demonstrate the chip capability for large-signal transmission, without using preemphasis or postemphasis, VLC with 16-quadrature amplitude modulation orthogonal frequency-division multiplexing transmission capacity up to 2 Gbit/s is achieved with an error vector magnitude of 17.07%, SNR of 15.35 dB, and bit error rate of $3.3 \times {10}^{-3}$ . Our LEDs embedded with PhCs pass the forward error correction criterion. The results reveal the advantages of LEDs with PhC for achieving higher data rate transmission.

In this study, a 50-Gb/s 16-quadrature amplitude modulation discrete multitone (16-QAM-DMT) was applied to an 850-nm oxide-confined vertical-cavity surface-emitting laser (VCSEL) at various temperature ranging from 25 °C to 85 °C. This study reports the highest bit rate for directly modulated VCSELs operating at 85 °C, in addition to demonstrating, for the first time, 16-QAM-DMT with less dependence on slope efficiency (SE) reduction. By using a temperature-compensated VCSEL, this study determined the degradation of the bit error rate (BER) in terms of the signal-to-noise ratio. The analysis results demonstrate that the transmission quality is dominated by optical bandwidth rather than the SE. Therefore, the preleveling technique was applied for error rate recovery to reduce the BER from $\text{6.3}\times \text{10}^{-3}$ to $\text{3.8}\times \text{10}^{-3}$ with a 0.2-dB/GHz preleveling slope. Thus, a low-bandwidth system (nearly 10 GHz) was realized for high data-rate transmissions (50 Gb/s) at 85 °C. The 16-QAM-DMT transmission provides an effective approach to alleviating thermal problems that occur in high-speed optical communication without the requirement of any external amplification circuits.

In this work, we demonstrate an IGZO TFT-based biosensor integrated with a microfluidic channel that can be used to monitor biochemical reactions between proteins and small molecules. The target biomaterials are applied to a Y-shaped microfluidic chamber while the reactant signal is readout by the TFT. Using Biotin-Streptavidin reaction as an example, the specific diffusion time of biotin, streptavidin, or streptavidin-biotin complex across the fluidic channel are benchmarked. By intentionally delaying the application of one specie to another, one can study properties of biochemical reactions, such as excess and exhaust conditions of the reactants, and the formation of the products while diffusing in the channel. The proposed TFT sensor provides an excellent platform in understanding the biochemical functions for the advance of biological science.

With the purpose to increase the threshold voltage of the enhancement mode GaN high-electron mobility transistors, we fabricated devices with gate field plates on the p-GaN/AlGaN/GaN/AlGaN double heterostructures. We observed an existence of a subthreshold region from the current–voltage transfer curves. The threshold voltage of the device extracted based on linear extrapolation method is much higher than that of a typical device without a gate field plate. We investigated electrical properties based on carrier distributions with the influence of gate electric field at different channel regions.

By changing the transverse-mode spectral linewidth of vertical cavity surface emitting lasers (VCSELs) at 850 nm, the directly encoded four-level pulse amplitude modulation data transmission performance over 100-m-long OM4 multimode fiber (MMF) are demonstrated and compared. The multi-mode VCSEL chip with the largest aperture of $11~\mu \text{m}$ reveals the widest spectral linewidth and the highest optical power, but provides the smallest modulation bandwidth to support only 44- and 28-Gb/s data rates for back-to-back (BtB) and 100-m OM4 MMF transmission cases, respectively. By shrinking the aperture size to reduce transverse-mode number, the few-mode VCSEL with the strongest throughput power enables a BtB transmission capacity as high as 52 Gb/s. However, its modal dispersion induced after OM4 MMF transmission inevitably degrade the data rate to 32 Gb/s. In contrast, the single-mode VCSEL with the smallest aperture of $3~\mu \text{m}$ reveals the highest modulation bandwidth and negligible modal dispersion to show competitive BtB transmission capacity with that of the few-mode VCSEL. In particular, the single-mode VCSEL successfully achieves a data rate of 34 Gb/s with a power penalty as low as 1.4 dB, after 100-m OM4 MMF transmission.

An 850-nm multi-mode vertical cavity surface emitting laser (VCSEL) bare chip with high-indium-density InGaAs/AlGaAs quantum-well pairs is demonstrated for directly encoded QAM-OFDM transmission in multi-mode fiber (MMF). By directly encoding the 850-nm VCSEL bare chip with a pre-leveled 14-GHz 16-QAM OFDM data, >50-Gb/s transmission over 100-m-long OM4 MMF can be realized without using data recovery circuit. Increasing the bias current of the VCSEL beyond 7.5Ith improves the signal-to-noise ratio (SNR) and the bit error ratio (BER) of received QAM-OFDM data to 15.5 dB and $2.9\times 10^{-3}$ , respectively. The 100-m-long OM4 MMF transmission degrades the SNR with its covered bandwidth reducing to 13 GHz. The OFDM subcarrier pre-leveling technique with a slope of 0.2 dB/GHz ensures the 16-QAM-OFDM data transmission with an error vector magnitude of 17.1% and a BER of $3.4\times 10^{-3}$ .

We demonstrated an integrated biosensor with a thin film transistor for recording electrical charges carried by bio-molecules and a microfluidic channel for detecting diffusion properties of the target solution. Using streptavidin and biotin as examples, the sensor is able to detect the binding interaction of streptavidin-biotin complexes by monitoring the transient responses of the transistor current. Our approach can be applied to the field of detection of protein–protein interactions.

Current collapse is a phenomenon that increases the channel resistance during the switching process when the high gate and drain voltages are applied. The effect can be found from GaN-based high-electron mobility transistors (HEMTs) and is an obstacle for their applications to power electronics. There have been numerous reports on suppressing current collapse using semiconductor process technologies. In this paper, an enhancement mode (E-mode) AlGaN/GaN/AlGaN double heterostructure was proposed. The current collapse phenomena were studied on devices of E-mode MIS and Schottky gate HEMTs. The results indicate the suppression of current collapse for devices with double heterostructure.

A transistor-based biosensor with high sensitivity is demonstrated in this paper. The sensor is composed of a reusable In–Ga–ZnO (IGZO)-thin-film transistor (TFT) array wire connected to an external sensing pool. The TFT acts as an electrical charge transducer as well as the signal readout device. Contrast to typical approachesofemploying parameters, such as transconductance, threshold voltage, or current change as the benchmark for sensitivity, we develop a model to extract the corresponding electrical changes after introducing analytes so as tomitigate device-to-device sensing variations. Using Epstein–Barr nuclear antigen-1 (EBNA-1) antibody as the example of target analyte, the IGZO-TFT biosensors are able to selectively detect 10 pg/mL of EBNA-1 antibody in the phosphate-buffered saline solution. The measurement results were cross verifiedwith conventional enzyme-linked immunosorbent assay (ELISA). Our approach is four orders of magnitude better than the ELISA.

This talk is aiming on presenting two novel detecting schemes that were developed in our lab. First of all, we demonstrate a highly sensitive IGZO TFT (thin film transistor) with dual gate electrodes that detects electric charges of the target biomaterial. The TFT also functions as a transducer for signal readout. An IGZO TFT-based biosensor integrated with a microfluidic channel can be further used to monitor biochemical reactions between proteins and small molecules. Using Biotin-Streptavidin reaction as an example, the specific diffusion time of biotin, streptavidin, or streptavidin-biotin complex across the fluidic channel are benchmarked. By intentionally delaying the application of one specie to another, we can study properties of biochemical reactions, such as excess and exhaust conditions of the reactants, and the formation of the products while diffusing in the channel. The proposed TFT sensor provides an excellent platform in understanding the biochemical functions for the advance of biological science Second, the target biomaterial can also be detected by a compact 2-dimensional hexagonal photonic crystals (PhCs). A critical wavelength that satisfies the phase matching or becomes evanescent is employed to benchmark the refractive index of the target analyte applied on the sensor. Using glucose solution as the example, our sensor demonstrates very high sensitivity and low limit of detection. It shows the diffraction mechanism from the hexagonal photonic crystals can be used for sensors when the compact size is a concern. The talk will spend a little bit of time comparing the sensitivity of both TFT and PhC sensors. Pros and cons of both approaches will be briefly mentioned.

We demonstrate a silicon via backend process for AlGaN/GaN-on-Si (111) platform-based devices which was processed by assisted back grinding, chemical mechanical polishing, deep reactive ion etching (DRIE) and copper (Cu) electroplating. The DC output characteristics can be improved about 20% after the introduction of backside via and copper heat dissipation layer. Moreover, the improvement also can be seen from the load-pull measurements under 20%, 25% and 30% duty cycle. Under higher pulse width operation, the more obvious improvement of output current can be observed. These results indicate that the substrate removal and copper filling technique are effective to achieve high-performance AlGaN/GaN HEMTs.

Recently, GaN based light-emitting diodes (LEDs) have been developed for visible light communication (VLC) with the increase of the usage in wireless data transmission. In this work, we successfully make the GaN-based LEDs with the photonic crystal (PhC) structure with high frequency response. Data transmission demonstrated using on-off keying (OOK) and 16- Quadrature Amplitude Modulation (QAM)- orthogonal frequency division multiplexing (OFDM) modulation methods on photonic crystal LEDs (PhCLEDs) and conventional LEDs (CLEDs).

The real-time monitoring of biotin-protein biochemical interaction was successful demonstrated by the In-Ga-Zn-O (IGZO) thin film transistor (TFT) biosensor integrated with microfluidic channel. The biomaterials diffused inside the microfluidic channel and attached on the sensing area of microfluidic channel. Then, the net charges carried by biomaterials induced the transient variation of drain current. The transient variation was analyzed to understand the diffusion properties. After the characterization of diffusion properties for reactants separately, it was possible to investigate the biochemical reaction. Based on the time and amount of drain current increment, the species and the exhaust or excess condition of biomaterials could be told respectively. In this work, the biotin-streptavidin reaction was monitored within 15 minutes. Not only the reactants, biotin and streptavidin, were sensed, but the product formation, biotin-streptavidin complex, was also observed from the measurement. By and large, there is a high potential for the method proposed here to be widely applied in biomedical engineering for the merits of time-saving, cost-efficiency, and simple-to-use.

In this study, we present a local substrate removal approach to suppress current collapse phenomenon for Al-GaN/GaN HEMT. For comparison, we made a conventional HEMT without substrate removal process. Result shows that the removal process has no negative effect on DC IV performance, instead, the drain current increase slightly after Si substrate removal, which may result from stress release due to lattice mismatch between Si and GaN. Then, pulse IV measurement is conducted using Keithley 2601a and Keithley 2651a to simultaneously provide gate and drain voltage pulse. Measurement results show that current collapse is strongly suppressed after Si substrate removal. Our findings suggest that current collapse may be related to not only buffer trap but also substrate trap, and Si substrate removal technique is an very effective way to mitigate current collapse phenomenon

The electrical characteristics and current collapse phenomenon of AlGaN/GaN/Si HEMTs after local Si substrate removal are investigated. Our study shows that removal process has no obvious impact on 2DEG density. However, we observe mitigation of current collapse after Si substrate removal, which is in contrast with a severe current degradation when we gradually increase the negative gate bias at pulse condition on the HEMTs with Si substrate. A physical model which involves strain relaxation and GaN buffer/Si interface defect reduction is employed to explain the electrical behavior.

Recent research and progress have shown that using light-emitting diodes (LEDs) as a high-speed transmitter is a promising candidate in a high-speed data system. The photonic crystal (PhC) LED (PhCLED) can improve the performance of the devices for visible light communication (VLC) due to its unique spatial and temporal management of photonic modes. In this paper, the dynamic behaviors of PhCLEDs at both small- and large-signal modulation are studied. Room-temperature time-resolved photoluminescence (TRPL) and Raman scattering measurements were carried out to understand the photon lifetime and strain in the PhC structure. PhCLEDs demonstrate much better high-frequency performance than conventional planar LEDs. Our study also shows that the common wisdom of shrinking the mesa size of LEDs to achieve high-frequency operation has its limit since the spontaneous emission rate has to be increased accordingly to maintain high light output efficiency in VLC LEDs.

The sensitivity of traditional diffraction grating sensors is limited by the spatial resolution of the measurement setup. Thus, a large space is required to improve sensor performance. Here, we demonstrate a compact hexagonal photonic crystal (PhC) optical sensor with high sensitivity. PhCs are able to diffract optical beams to various angles in azimuthal space. The critical wavelength that satisfies the phase matching or becomes evanescent was used to benchmark the refractive index of a target analyte applied on a PhC sensor. Using a glucose solution as an example, our sensor demonstrated very high sensitivity and a low limit of detection. This shows that the diffraction mechanism of hexagonal photonic crystals can be used for sensors when compact size is a concern.

Semiconductor nanocomposites provide advantages beyond the capability of typical fluorescent materials for cancer detection. In this work, nanowire-based probes with dual color channels are employed to demonstrate the capacity of cancer cell detection. Purple emitting ZnO/antibody probes are applied to detect cancer cells and meanwhile TiO2 /antibody probes with green light emission are applied to identify normal fibroblast cells. A series of quantitative analyses are conducted to verify the correlation between the concentrations of ZnO and TiO2 probes, cell numbers, and peak intensities of the PL spectra. The results provide a quantitative reference for developing nanowire-based cancel cell probes.

We demonstrate a novel design of large-size device in AlGaN/GaN high-electron-mobility transistor (HEMT). Depletion mode (D-mode) HEMTs and enhancement mode (E-mode) HEMTs are fabricated in our research. The saturation current of D-mode HEMTs is over 6A. By using Cascode structure, the D-mode HEMT becomes a normally-off device efficiently, and the threshold voltage of it rises from-7V to 2V. By using BCB (Benzocyclobutene) as the passivation, the E-mode HEMT shows an excellent characteristic. Also, when the VGS of the E-mode HEMT is over 9V, it still shows a good performance.