Efficiency GaN Research Articles

GaN-based E-mode p-FETs with polarization-doped p-type graded AlGaN channels

Herein, a novel enhancement-mode (E-mode) GaN-based p-channel FETs (p-FETs) with a linearly graded AlGaN (LGA) p-channel is proposed and numerically studied by Silvaco TCAD. Thanks to strong polarization-induced doping, three-dimensional hole gas (3DHG) can be uniformly generated in LGA to form a continuous p-channel with a hole concentration over 1018 cm–3. Combined with an optimized recessed gate structure, the LGA p-FET can simultaneously achieve a large threshold voltage (|V TH|) > 2 V and a high current density (|J DS|) of ∼10 mA mm−1 at V DS = −10 V. Additionally, two critical parameters of the LGA p-FETs, i.e. the depth of recessed gate and initial Al composition of LGA, are specifically studied to reveal the unique carrier behavior of 3DHG in the devices. Importantly, the LGA structure is further optimized and implemented as the p-type cap layer to construct an E-mode GaN n-FET. Thereby, based on the same LGA configuration, a GaN-based inverter with the matched complementary n- and p-FETs is monolithically constructed, showing sharp voltage transition. The reported novel LGA structure and its availability in both GaN-based E-mode n- and p-FETs provides valuable insights and guidance to construct highly efficient GaN p-type devices and All-GaN-based integrated circuits for compact power electronic systems.

High Efficiency of 5 μm‐Diameter Blue Micro‐Light‐Emitting Diodes

Small‐size pixels and high efficiency under low injection levels are required for high‐resolution microdisplay. Efficient blue InGaN micro‐light‐emitting diodes (μLEDs) with 5 μm diameter are fabricated using AuSn flip‐chip bonding, high reflection electrodes, and large‐area N electrodes surrounding the mesas. The peak external quantum efficiency (EQE) measured in an integrating sphere is as high as 13.67% at a current density of 5.4 A cm−2. Moreover, at a current density of 0.1 A cm−2, EQE can still reach 11.69%. The electrical efficiency approaches 1, and the differential slope of log L versus log I is close to 1 at low current density. These results suggest significant progress in exploring high‐efficiency 5 μm InGaN blue μLEDs.

High efficiency GaN power amplifier with compact harmonic tuning network

AbstractOne high efficiency second harmonic tuned (2HT) power amplifier (PA) with a compact multi‐harmonic tuning network is presented. The proposed design method can drive the third harmonic impedance to short‐circuit condition to achieve an ideal 2HT PA operation. Then the second harmonic impedance is controlled to proper position to improve the PA efficiency. Meanwhile, the fundamental impedance is also transferred to 50 Ω load by making the most of this tuning network. Consequently, the proposed output network can be designed to a compact size and is suitable for high frequency PA applications. For demonstration, a PA using Cree CGH40010 GaN high‐electron‐mobility transistor is designed and fabricated at 3.5 GHz. The measured results show that the PA achieves peak power added efficiency of 72.8%, output power of 41.3 dBm and drain efficiency of 80.2% at 3.3 GHz.

A Novel Enhancement-Mode Gallium Nitride p-Channel Metal Insulator Semiconductor Field-Effect Transistor with a Buried Back Gate for Gallium Nitride Single-Chip Complementary Logic Circuits

In this work, a novel enhancement-mode GaN p-MISFET with a buried back gate (BBG) is proposed to improve the gate-to-channel modulation capability of a high drain current. By using the p-GaN/AlN/AlGaN/AlN double heterostructure, the buried 2DEG channel is tailored and connected to the top metal gate, which acts as a local back gate. Benefiting from the dual-gate structure (i.e., top metal gate and 2DEG BBG), the drain current of the p-MISFET is significantly improved from −2.1 (in the conv. device) to −9.1 mA/mm (in the BBG device). Moreover, the dual-gate design also bodes well for the gate to p-channel control; the subthreshold slope (SS) is substantially reduced from 148 to ~60 mV/dec, and such a low SS can be sustained for more than 3 decades. The back gate effect and the inherent hole compensation mechanism of the dual-gate structure are thoroughly studied by TCAD simulation, revealing their profound impact on enhancing the subthreshold and on-state characteristics in the BBG p-MISFET. Furthermore, the decent device performance of the proposed BBG p-MISFET is projected to the complementary logic inverters by mixed-mode simulation, showcasing excellent voltage transfer characteristics (VTCs) and dynamic switching behavior. The proposed BBG p-MISFET is promising for developing GaN-on-Si monolithically integrated complementary logic and power devices for high efficiency and compact GaN power IC.

An efficiently excited Eu3+ luminescent site formed in Eu,O-codoped GaN

For the development of III-nitride-semiconductor-based monolithic micro-light-emitting diode (LED) displays, Eu,O-codoped GaN (GaN:Eu,O) is a promising material candidate for the red LEDs. The luminescence efficiency of Eu-related emission strongly depends on the local atomic structure of Eu ions. Our previous research has revealed that post-growth thermal annealing is an effective method for reconfiguring luminescent sites, leading to a significant increase in light output. We observed the preferential formation of a site with a peak at ∼2.004 eV by the annealing process. In this study, we demonstrate that it is a previously unidentified independent site (OMVPE-X) using combined excitation–emission spectroscopy and time-resolved photoluminescence measurements. In addition, we perform excitation power-dependent photoluminescence measurements and show that this OMVPE-X site dominates the emission at a low excitation power region despite its small relative abundance, suggesting a high excitation efficiency. Most importantly, applying our annealing technique to an LED exhibits a reasonably increased electroluminescence intensity associated with OMVPE-X, confirming that this site has a high excitation efficiency also under current injection. These results demonstrate the importance of OMVPE-X as a notable luminescent site for brighter and more efficient GaN:Eu,O-based LEDs.

Design of a Highly Efficient Class-F GaN MMIC Power Amplifier Using a Multi-Function Bias Network and a Harmonic-Isolation L-C Resonator

Design of a Highly Efficient Class-F GaN MMIC Power Amplifier Using a Multi-Function Bias Network and a Harmonic-Isolation L-C Resonator

High external quantum efficiency (6.5%) InGaN V-defect LEDs at 600 nm on patterned sapphire substrates

Highly efficient long-wavelength InGaN LEDs have been a research focus in nitride LEDs for their potential applications in displays and solid-state lighting. A key breakthrough has been the use of laterally injected quantum wells via naturally occurring V-defects which promote hole injection through semipolar sidewalls and help to overcome the barriers to carrier injection that plague long wavelength nitride LEDs. In this article, we study V-defect engineered LEDs on (0001) patterned sapphire substrates (PSS) and GaN on (111) Si. V-defects were formed using a 40-period InGaN/GaN superlattice and we report a packaged external quantum efficiency (EQE) of 6.5% for standard 0.1 mm2. LEDs on PSS at 600 nm. We attribute the high EQE in these LEDs to lateral injection via V-defects.

Orthogonal Filter Frequency Followed by LNA Linearity Tuning for Efficient Instinctual GaN Receiver Front-End

Orthogonal Filter Frequency Followed by LNA Linearity Tuning for Efficient Instinctual GaN Receiver Front-End

A Multioutput and Highly Efficient GaN Distributed Power Amplifier for Compact Subarrays in Wideband Phased Array Antennas

This article presents the design, implementation, and measurement results of a multioutput distributed power amplifier (MODPA) in 100-nm AlN–GaN–AlGaN high-electron-mobility transistor (HEMT) on a silicon substrate. The proposed MODPA improves power-added efficiency (PAE) in distributed amplifiers (DAs) by not wasting reverse traveling waves and delivering all forward and reverse waves to the output ports. Utilizing MODPA in implementing a subarray-based phased-array transceiver reduces the number of power splitters and PAs, significantly reducing the subarray’s chip area and power loss. A design methodology for broadband, efficient amplifier implementation by optimizing load/source impedances at the fundamental and harmonic frequencies is presented based on comprehensive source/load—pull simulations and class-J dynamic load lines. The presented broadband design methodology addresses an ambiguity for picking optimum load/source impedance at a single frequency caused by higher order harmonics of operating frequencies dropping in the band. The fabricated MODPA occupies a 1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> 3 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{2}$</tex-math> </inline-formula> chip area. In 0.01–25-GHz frequency, MODPA delivered 37–41-dBm power to the four outputs, with a 17–21-dB total power gain and 22%–73% total PAE. The power gain and phase variation between the four matched-output ports are less than 1.5 dB and 3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> , respectively, making MODPA an attractive design for implementing subarrays.

Enhancement of Short-Circuit Current Density in Superlattice-Based InGaN/GaN Solar Cells

In this paper, the mechanism of short-circuit current density (JSC) enhancement in InGaN/GaN superlattices(SLs)-structured solar cells (SCs) is investigated theoretically and experimentally, and compared with conventional InGaN/GaN multiple quantum wells (MQWs) SCs. Due to the ultrathin structure of the X-ray diffraction SLs, a tunneling model is introduced in Silvaco software. The simulation results show that the trend of the simulation results is consistent with the experimental values. Due to the contribution of the tunneling effect, the JSC of SCs with SLs structure is greatly improved, but the open circuit voltage (VOC) is also reduced due to defects in the growth process of epitaxial wafers with SLs structure. These observations suggest that tunneling effects increase the JSC of the SCs, thus improving the photovoltaic conversion efficiency (PCE) of SCs. This study provides evidence for the fabrication of highly efficient InGaN SCs.

Generative adversarial networks based skin lesion segmentation

Skin cancer is a serious condition that requires accurate diagnosis and treatment. One way to assist clinicians in this task is using computer-aided diagnosis tools that automatically segment skin lesions from dermoscopic images. We propose a novel adversarial learning-based framework called Efficient-GAN (EGAN) that uses an unsupervised generative network to generate accurate lesion masks. It consists of a generator module with a top-down squeeze excitation-based compound scaled path, an asymmetric lateral connection-based bottom-up path, and a discriminator module that distinguishes between original and synthetic masks. A morphology-based smoothing loss is also implemented to encourage the network to create smooth semantic boundaries of lesions. The framework is evaluated on the International Skin Imaging Collaboration Lesion Dataset. It outperforms the current state-of-the-art skin lesion segmentation approaches with a Dice coefficient, Jaccard similarity, and accuracy of 90.1%, 83.6%, and 94.5%, respectively. We also design a lightweight segmentation framework called Mobile-GAN (MGAN) that achieves comparable performance as EGAN but with an order of magnitude lower number of training parameters, thus resulting in faster inference times for low compute resource settings.

High-density 2D hole gas in p-GaN/AlN/AlGaN on a silicon substrate with polarization-enhanced Mg ionization

Improving the hole concentration in p-GaN specimens has posed a major challenge due to the high activation energy of Mg doping in GaN. Recently, a delta doping technique for modulating the valence band and increasing the Mg ionization efficiency in GaN has been proposed. However, the memory effect of Mg in the reaction chamber greatly increases the difficulty of epitaxial growth; additionally, the Mg ionization efficiency remains too low. In this study, we demonstrate a novel p-GaN/AlN/AlGaN structure with an increased Mg ionization efficiency, from 5.16% to 14.22%, relative to the conventional p-GaN/AlGaN structure. The inserted AlN layer effectively modulates the valence band of p-GaN near the p-GaN/AlN interface and decreases the activation energy, as confirmed by density functional theory and the 1D Poisson–Schrodinger equation. Moreover, a high-performance p-channel GaN FinFET with a high output current of 114 mA/mm is fabricated, and the polarization-enhanced epitaxial layer shows great promise for next-generation digital ICs.

Design of a wideband highly efficient GaN HEMT power amplifier for multiband applications

AbstractA distributed basic matching network (MN) designed method that can achieve multioctave bandwidth and highly efficient power amplifier (PA) for multiband applications is presented in this letter. The distributed network unit with a left-rotating T-type structure is employed to construct the wideband MN, whose topology and circuit parameters are acquired through optimization. Finally, the impedance realized by the designed MN falls into the target impedance region obtained by using multi-harmonic bilateral pull technique in the desired frequency band. For the proof of the method, a broadband highly efficient PA has been designed, fabricated, and measured using commercialized GaN high electron mobility transistors (HEMT). The measured results show that the implemented PA achieves a bandwidth of 137.8% from 0.7 to 3.8 GHz. The drain efficiency is between 59% and 70% with an output power of greater than 39 dBm and a gain ranging from 9 to 12.1 dB.

Solid-State Power Combining for Heating Small Volumes of Mixed Waste Materials

Microwave heating of waste results in chemical breakdown that can lead to conversion of mixed waste materials to fuel. Heating waste mixtures with microwave energy rather than incineration results in faster breakdown and can therefore be more efficient. Here we address heating of small volumes of mixed food waste materials with widely differing and temperature-dependent electrical properties. Uniform heating is accomplished with mode mixing within a loaded cavity and by spatial power combining of solid-state power amplifiers (SSPAs). We present a heating comparison of two circuit-combined and spatially-combined 2.45 GHz 70-W 65% efficient GaN SSPAs with controlled relative phase. The heating efficacy is shown to improve by volumetric combining inside the waste loading. The temperature changes in several locations and for several common waste materials and mixtures are investigated and compared to FEM electromagnetic simulations, as well as FDTD multi-physics simulations that incorporate thermal dependence of material properties. The approach is scalable in volume and power, demonstrated by a simulation comparison of the 1.4 L small cavity to a 5.2 L volume.

12‐3: Invited Paper: Nanowire Micro‐LEDs for Augmented Reality and Virtual Reality (AR/VR) Displays

We report on high efficiency InGaN nanowire‐based micro and nanoscale light emitting diodes (LEDs). We show that record‐ high efficiency and highly directional emissions can be achieved with red and green submicron nanowire micro‐LEDs. Such LEDs are critical for augmented reality displays which require both efficiency and high optical throughput.

Significant Quantum Efficiency Enhancement of InGaN Red Micro-Light-Emitting Diodes with a Peak External Quantum Efficiency of up to 6%

We demonstrate a significant quantum efficiency enhancement of InGaN red micro-light-emitting diodes (μLEDs). The peak external quantum efficiency (EQE) of the packaged 80 × 80 μm2 InGaN red μLEDs was largely increased to 6.0% at 12 A/cm2, representing the significant process in exploring the efficiency of InGaN red μLEDs. The improvement of the EQE is attributed to the significant enhancement of the quantum efficiency, which is confirmed by the electron–hole wavefunction overlap in the InGaN quantum well from the band gap simulation and the photoluminescence intensity ratio at room temperature/low temperature. Ultrasmall 5 × 5 μm2 InGaN red μLEDs were also obtained, which show a high peak EQE of 4.5%. This work demonstrates a simple approach to achieving highly efficient InGaN red μLEDs, which are very promising candidates for ultrasmall red μLEDs required by AR/VR displays.

Development of Low-Resistance Ohmic Contacts with Bilayer NiO/Al-Doped ZnO Thin Films to p-type GaN

The fabrication of low-resistance and thermally stable Ohmic contacts is essential for the realization of reliable GaN power devices. In the particular case of p-type GaN, a thin Ni/Au bilayer is commonly used for Ohmic contacts. However, Au metal contacts are quite expensive, are incompatible with the complementary metal oxide-semiconductor foundries, and also have poor thermal stability. Thus, seeking an alternative that is affordable and thermally stable is crucial. In the present study, we investigate Au-free Ohmic contact formation on p-type GaN using a bilayer Ni/Al-doped ZnO (AZO) thin film. Careful studies were focused on identifying the role of process parameters such as annealing parameters: temperature, time, and atmosphere in order to obtain an excellent Ohmic contact on p-GaN. Our results show that the contact resistance can be significantly reduced using a Ni/AZO bilayer with a suitable rapid thermal process. We demonstrate that the specific contact resistance for Ni/AZO on p-GaN can reach the lowest value of 1.85 × 10-4 Ω·cm2 for a sample with a 5 nm Ni layer annealed at 500 °C in air for 5 min. Our work demonstrates that the bilayer Ni/AZO contact could be suitable for efficient GaN power diodes or transistors.

Dy3+ and Tb3+ codoped mixed garnet crystals with a high-disorder structure for promising efficient InGaN laser-diode pumped yellow lasers

Dy3+ and Tb3+ codoped mixed garnet crystals with a high-disorder structure were grown by the Cz method. These mixed crystals exhibit distinct advantages for the development of blue laser diode pumped one-step solid-state yellow lasers.

Tailoring the performance of GaN-based yellow light-emitting diodes

Efficient yellow InGaN light-emitting diodes (LEDs) have been a challenge for the researchers. To achieve yellow emission, high indium composition is necessary. However, high indium composition comes with its own challenges. In our work, the performance of InGaN yellow light emitting diodes is improved by using quaternary (AlInGaN) quantum barriers and ternary (AlGaN) quantum barriers in the conventional InGaN/GaN LED. We show that employing AlGaN quantum barriers in the light-emitting diodes significantly increases the concentration of electrons as well as holes, resulting in a 47% increase in radiative recombination rate than the conventional yellow LED. Additionally, the efficiency droop is significantly reduced in our proposed LEDs.

Anomaly Detection of Lung Sounds Using Deep Neural Networks

To find lung diseases, physicians need to conduct various examinations. Recently, to reduce their burdens, many applications of deep learning have been proposed to diagnose chest X-ray images. However, there are few studies using deep learning for auscultation, and also, there are only a few small-scale benchmark datasets of lung sounds that are annotated for machine learning. Therefore, we aim to build an anomaly detection system that only uses normal data for the training. When building anomaly detection systems, it is important to capture generalized features based only on the normal data. To solve this problem, first, we propose some algorithms that improve the Deep Autoencoding Gaussian Mixture Model (DAGMM). Second, we propose some algorithms that improves Efficient GAN. Various types of neural networks such as CNN, LSTM, and convolutional LSTM (C-LSTM) are applied to DAGMM, and GMM and C-LSTM are applied to Efficient GAN for effective feature extraction. The experimental results show that each of the proposed methods has effective classification performance for lung sounds, and especially, the combination of convolution and LSTM, and the combination of feature extraction and GMM are effective for any of the models.