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Microstructural Characterization of GaN Grown on SiC
Sabyasachi Saha, Deepak Kumar, Chandan K. Sharma, Vikash K. Singh, Samartha Channagiri, Duggi V. Sridhara Rao
Journal: Microscopy and Microanalysis / Volume 25 / Issue 6 / December 2019
Published online by Cambridge University Press: 01 August 2019, pp. 1383-1393
Print publication: December 2019
GaN films have been grown on SiC substrates with an AlN nucleation layer by using a metal organic chemical vapor deposition technique. Micro-cracking of the GaN films has been observed in some of the grown samples. In order to investigate the micro-cracking and microstructure, the samples have been studied using various characterization techniques such as optical microscopy, atomic force microscopy, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy (TEM). The surface morphology of the AlN nucleation layer is related to the stress evolution in subsequent overgrown GaN epilayers. It is determined via TEM evidence that, if the AlN nucleation layer has a rough surface morphology, this leads to tensile stresses in the GaN films, which finally results in cracking. Raman spectroscopy results also suggest this, by showing the existence of considerable tensile residual stress in the AlN nucleation layer. Based on these various observations and results, conclusions or propositions relating to the microstructure are presented.
A low-phase noise D-band signal source based on 130 nm SiGe BiCMOS and 0.15 µm AlGaN/GaN HEMT technologies
Thanh Ngoc Thi Do, Mingquan Bao, Zhongxia Simon He, Ahmed Hassona, Dan Kuylenstierna, Herbert Zirath
Journal: International Journal of Microwave and Wireless Technologies / Volume 11 / Issue 5-6 / June 2019
Published online by Cambridge University Press: 25 March 2019, pp. 456-465
This paper reports on a record-low-phase noise D-band signal source with 5 dBm output power, and 1.3 GHz tuning range. The source is based on the unconventional combination of a fundamental frequency 23 GHz oscillator in 150 nm AlGaN/GaN HEMT technology followed by a 130 nm SiGe BiCMOS MMIC including a sixtupler and an amplifier. The amplifier operates in compression mode as power-limiting amplifier, to equalize the source output power so that it is nearly independent of the oscillator's gate and drain bias voltages used for tuning the frequency of the source. The choice of using a GaN HEMT oscillator is motivated by the need for a low oscillator noise floor, which recently has been demonstrated as a bottle-neck for data rates in wideband millimeter-wave communication systems. The phase noise performance of this signal source is −128 dBc/Hz at 10 MHz-offset. To the best of the authors' knowledge, this result is the lowest reported phase noise of D-band signal source.
A streamlined drain-lag model for GaN HEMTs based on pulsed S-parameter measurements
Peng Luo, Frank Schnieder, Olof Bengtsson, Valeria Vadalà, Antonio Raffo, Wolfgang Heinrich, Matthias Rudolph
Journal: International Journal of Microwave and Wireless Technologies / Volume 11 / Issue 2 / March 2019
Accurately and efficiently modeling the drain-lag effects is crucial in nonlinear large-signal modeling for Gallium Nitride high electron mobility transistors. In this paper, a simplified yet accurate drain-lag model based on an industry standard large-signal model, i.e., the Chalmers (Angelov) model, extracted by means of pulsed S-parameter measurements, is presented. Instead of a complex nonlinear drain-lag description, only four constant parameters of the proposed drain-lag model need to be determined to accurately describe the large impacts of the drain-lag effects, e.g., drain-source current slump, typical kink observed in pulsed IV curves, and degradation of the output power. The extraction procedure of the parameters is based on pulsed S-parameter measurements, which allow to freeze traps and isolate the trapping effects from self-heating. It is also shown that the model can very accurately predict the load pull performance over a wide range of drain bias voltages. Finally, the large-signal network analyzer measurements at low frequency are used to further verify the proposed drain-lag model in the prediction of the output current in time domain under large-signal condition.
Charge-conservative GaN HEMT nonlinear modeling from non-isodynamic multi-bias S-parameter measurements
Gian Piero Gibiino, Alberto Santarelli, Fabio Filicori
Guaranteeing charge conservation of empirically extracted Gallium Nitride (GaN) High-Electron-Mobility Transistor (HEMT) models is necessary to avoid simulation issues and artifacts in the prediction. However, dispersive effects, such as thermal and charge-trapping phenomena, may compromise the model extraction flow resulting in poor model accuracy. Although GaN HEMT models should be extracted, in principle, from an isodynamic dataset, this work deals with the systematic identification of an approximate, yet most suitable, charge-conservative empirical model from standard multi-bias S-parameters, i.e., from non-isodynamic data. Results show that the obtained model maintains a reasonable accuracy in predicting both small- and large-signal behavior, while providing the benefits of charge conservation.
Arithmetic intersection on GSpin Rapoport–Zink spaces
Lie groups
Arithmetic problems. Diophantine geometry
Arithmetic algebraic geometry
Chao Li, Yihang Zhu
Journal: Compositio Mathematica / Volume 154 / Issue 7 / July 2018
Published online by Cambridge University Press: 16 May 2018, pp. 1407-1440
Print publication: July 2018
We prove an explicit formula for the arithmetic intersection number of diagonal cycles on GSpin Rapoport–Zink spaces in the minuscule case. This is a local problem arising from the arithmetic Gan–Gross–Prasad conjecture for orthogonal Shimura varieties. Our formula can be viewed as an orthogonal counterpart of the arithmetic–geometric side of the arithmetic fundamental lemma proved by Rapoport–Terstiege–Zhang in the minuscule case.
Transfer of AlGaN/GaN RF-devices onto diamond substrates via van der Waals bonding
Thomas Gerrer, Volker Cimalla, Patrick Waltereit, Stefan Müller, Fouad Benkhelifa, Thomas Maier, Heiko Czap, Oliver Ambacher, Rüdiger Quay
We present a novel bonding process for gallium nitride-based electronic devices on diamond heat spreaders. In the proposed technology, GaN devices are transferred from silicon (Si) onto single (SCD) and polycrystalline diamond (PCD) substrates by van der Waals bonding. Load-pull measurements on Si and SCD heat spreaders at 3 GHz and 50 V drain bias show comparable power-added-efficiency and output power (Pout) levels. A thermal analysis of the hybrids was performed by comparison of 2 × 1mm2 AlGaN/GaN Schottky diodes on Si, PCD, and SCD, which exhibit a homogeneous field in the channel in contrast to gated transistors. Significantly different currents are observed due to the temperature dependent mobility in the 2DEG channel. These measurements are supported by a 3D thermal finite element analysis, which suggests a large impact of our transfer technique on the thermal resistance of these devices. In summary, we show a promising new GaN-on-diamond technology for future high-power, microwave GaN device applications.
Sidelobe reduction with a GaN active array antenna
Wirelessly Powering: The Future
Naoki Hasegawa, Naoki Shinohara
Journal: Wireless Power Transfer / Volume 4 / Issue 2 / September 2017
Published online by Cambridge University Press: 21 November 2017, pp. 113-119
Print publication: September 2017
This work proposes a tunable sidelobe reduction method based on a GaN active-antenna technique, in which the output radio frequency power is controlled by the DC drain voltage of the amplifiers. In this study, a 1 × 4 array of active antenna with GaN amplifiers is designed and fabricated. GaN amplifiers capable of up to 10 W-class power output are fabricated and arranged for a four-way active-array antenna. The fabricated single-stage GaN amplifier offers a maximum power-added efficiency of 59.6% and a maximum output power of 39.3 dBm. The maximum output power is decreased to 36.5 dBm upon decreasing the operating drain voltage from 55 to 35 V. In this study, a 4.5 dB sidelobe reduction is demonstrated in a 1 × 4 active antenna based on this output power difference for each amplifier.
Thinking Outside the Circle: Reflections on Theory and Methods for School-Based Garden Research
Liesa Clague, Neil Harrison, Katherine Stewart, Caroline Atkinson
Journal: The Australian Journal of Indigenous Education / Volume 47 / Issue 2 / December 2018
Published online by Cambridge University Press: 24 July 2017, pp. 139-145
School-based gardens (SBGs) are contributing to improvements in many areas of education, including nutrition, health, connectedness and engagement of students. While considerable research has been conducted in other parts of the world, research in Australia provides limited understanding of the impact of SBGs. The aim of this paper is to give a reflective viewpoint on the impact of SBGs in Australia from the perspective of an Aboriginal philosophical approach called Dadirri. The philosophy highlights an Australian Aboriginal concept, which exists but has different meanings across Aboriginal language groups. This approach describes the processes of deep and respectful listening. The study uses photovoice as a medium to engage students to become researchers in their own right. Using this methodology, students have control over how they report what is significant to them. The use of photovoice as a data collection method is contextualised within the Aboriginal philosophical approach to deep listening. For the first author, an Aboriginal researcher (Clague), the journey is to find a research process that maintains cultural integrity and resonates with the participants by affirming that a culturally sensitive approach to learning is important.
Multi-Octave bandwidth, 100 W GaN power amplifier using planar transmission line transformer
Mhd Tareq Arnous, Zihui Zhang, Felix Rautschke, Georg Boeck
Journal: International Journal of Microwave and Wireless Technologies / Volume 9 / Issue 6 / July 2017
Published online by Cambridge University Press: 08 March 2017, pp. 1261-1269
In this paper, design, implementation, and experimental results of efficient, high-power, and multi-octave gallium nitride-high electron mobility transistor power amplifier are presented. To overcome the low optima source/load impedances of a large transistor, various topologies of a broadside-coupled impedance transformer are simulated, implemented, and measured. The used transformer has a flat measured insertion loss of 0.5 dB and a return loss higher than 10 dB over a decade bandwidth (0.4–4 GHz). The transformer is integrated at the drain and gate sides of the transistor using pre-matching networks to transform the complex optima source/load impedances to the appropriate impedances of the transformer plane. The measurement results illustrate a saturated output power ranged between 80 and 115 W with an average drain efficiency of 57% and gain of 10.5 dB across 0.6–2.6 GHz.
Refined global Gan–Gross–Prasad conjecture for Fourier–Jacobi periods on symplectic groups
Discontinuous groups and automorphic forms
Hang Xue
Journal: Compositio Mathematica / Volume 153 / Issue 1 / January 2017
Published online by Cambridge University Press: 19 January 2017, pp. 68-131
Print publication: January 2017
In this paper, we propose a conjectural identity between the Fourier–Jacobi periods on symplectic groups and the central value of certain Rankin–Selberg $L$ -functions. This identity can be viewed as a refinement to the global Gan–Gross–Prasad conjecture for $\text{Sp}(2n)\times \text{Mp}(2m)$ . To support this conjectural identity, we show that when $n=m$ and $n=m\pm 1$ , it can be deduced from the Ichino–Ikeda conjecture in some cases via theta correspondences. As a corollary, the conjectural identity holds when $n=m=1$ or when $n=2$ , $m=1$ and the automorphic representation on the bigger group is endoscopic.
A high-power solid state amplifier for Galileo satellite system exploiting European GaN technology
Rocco Giofré, Paolo Colantonio, Elisa Cipriani, Franco Giannini, Laura Gonzalez, Francisco De Arriba, Lorena Cabria
Journal: International Journal of Microwave and Wireless Technologies / Volume 8 / Issue 4-5 / June 2016
This paper describes the development of an L-Band (f0 = 1.575 GHz) high power and efficient solid state power amplifier (SSPA) designed for the European satellite navigation system (i.e. Galileo). The amplifier, developed in the framework of the European Project named SLOGAN, exploits the GH50-10 GaN technology available at United Monolithic Semiconductor foundry. The aim of the project is to offer, using as much as possible European technologies, a valid alternative to replace traveling wave tube amplifiers with more compact and reliable systems. All the SSPA functionalities, i.e. power supply, power conditioning and radio frequency amplification, are integrated in the developed architecture and accommodated in a single box with limited volume and mass. The required output power level is achieved by parallelizing several GaN die power bars of 12 and/or 25.6 mm. In continuous wave operating mode, the overall SSPA delivers an output power higher than 250 W at less than 2 dB of gain compression in the whole E1-band. Moreover, the registered gain and efficiency are higher than 67 dB and 54%, respectively.
PERIODS OF AUTOMORPHIC FORMS: THE TRILINEAR CASE
Shunsuke Yamana
Journal: Journal of the Institute of Mathematics of Jussieu / Volume 17 / Issue 1 / February 2018
Published online by Cambridge University Press: 26 October 2015, pp. 59-74
Following Jacquet, Lapid and Rogawski, we regularize trilinear periods. We use the regularized trilinear periods to compute Fourier–Jacobi periods of residues of Eisenstein series on metaplectic groups, which has an application to the Gan–Gross–Prasad conjecture.
Optical properties of defects in nitride semiconductors
Ingo Tischer, Matthias Hocker, Benjamin Neuschl, Manfred Madel, Martin Feneberg, Martin Schirra, Manuel Frey, Manuel Knab, Pascal Maier, Thomas Wunderer, Robert A.R. Leute, Junjun Wang, Ferdinand Scholz, Johannes Biskupek, Jörg Bernhard, Ute Kaiser, Ulrich Simon, Levin Dieterle, Heiko Groiss, Erich Müller, Dagmar Gerthsen, Klaus Thonke
Journal: Journal of Materials Research / Volume 30 / Issue 20 / 28 October 2015
Published online by Cambridge University Press: 23 September 2015, pp. 2977-2990
Print publication: 28 October 2015
Group III nitrides are promising materials for light emitting diodes (LEDs). The occurrence of structural defects strongly affects the efficiency of these LEDs. We investigate the optical properties of basal plane stacking faults (BFSs), and the assignment of specific spectral features to distinct defect types by direct correlation of localized emission bands measured by cathodoluminescence in a scanning electron microscope with defects found in high resolution (scanning) transmission electron microscopy and electron beam induced current at identical sample spots. Thus, we are able to model the electronic structure of BSFs addressing I1, I2, and E type BSFs in GaN and AlGaN with low Al content. We find hints that BSFs in semipolar AlGaN layers cause local changes of the Al content, which strongly affects the usability of AlGaN as an electron blocking layer in nitride based LEDs.
Practical Issues for Atom Probe Tomography Analysis of III-Nitride Semiconductor Materials
Fengzai Tang, Michael P. Moody, Tomas L. Martin, Paul A.J. Bagot, Menno J. Kappers, Rachel A. Oliver
Journal: Microscopy and Microanalysis / Volume 21 / Issue 3 / June 2015
Various practical issues affecting atom probe tomography (APT) analysis of III-nitride semiconductors have been studied as part of an investigation using a c-plane InAlN/GaN heterostructure. Specimen preparation was undertaken using a focused ion beam microscope with a mono-isotopic Ga source. This enabled the unambiguous observation of implantation damage induced by sample preparation. In the reconstructed InAlN layer Ga implantation was demonstrated for the standard "clean-up" voltage (5 kV), but this was significantly reduced by using a lower voltage (e.g., 1 kV). The characteristics of APT data from the desorption maps to the mass spectra and measured chemical compositions were examined within the GaN buffer layer underlying the InAlN layer in both pulsed laser and pulsed voltage modes. The measured Ga content increased monotonically with increasing laser pulse energy and voltage pulse fraction within the examined ranges. The best results were obtained at very low laser energy, with the Ga content close to the expected stoichiometric value for GaN and the associated desorption map showing a clear crystallographic pole structure.
Endoscopie et conjecture locale raffinée de Gan–Gross–Prasad pour les groupes unitaires
Linear algebraic groups and related topics
R. Beuzart-Plessis
Published online by Cambridge University Press: 18 February 2015, pp. 1309-1371
Under endoscopic assumptions about $L$ -packets of unitary groups, we prove the local Gan–Gross–Prasad conjecture for tempered representations of unitary groups over $p$ -adic fields. Roughly, this conjecture says that branching laws for $U(n-1)\subset U(n)$ can be computed using epsilon factors.
Effect of p-GaN layer on the properties of InGaN/GaN green light-emitting diodes
Wenliang Wang, Zuolian Liu, Shizhong Zhou, Weijia Yang, Yunhao Lin, Haiyan Wang, Zhiting Lin, Huirong Qian, Guoqiang Li
Journal: Journal of Materials Research / Volume 30 / Issue 4 / 28 February 2015
Print publication: 28 February 2015
InGaN/GaN green light-emitting diodes (LEDs) have been prepared by metal-organic chemical vapor deposition with various growth temperatures for p-GaN layer. The structural and optoelectronic properties of as-grown multiple quantum wells (MQWs) and LEDs are studied in detail. It reveals that with the growth of p-GaN layer, the crystalline qualities of the as-grown n-GaN layer are improved significantly, while the optoelectronic properties of MQWs are decreased dramatically. Furthermore, the mechanisms for the effect of p-GaN growth temperature on the properties of InGaN/GaN green LEDs are proposed. It is demonstrated that the p-GaN layer grown at a suitable temperature of 950 °C shows the highest optoelectronic properties due to the fact that this suitable temperature for p-layer growth is good for the Mg doping and would not cause the fluctuation of indium in the MQWs, and eventually benefits to the effective recombination of carriers. This work provides an optimized p-GaN layer growth temperature for realizing highly efficient InGaN/GaN green LED devices.
Periods of automorphic forms: the case of $(\text{GL}_{n+1}\times \text{GL}_{n},\text{GL}_{n})$
Atsushi Ichino, Shunsuke Yamana
Journal: Compositio Mathematica / Volume 151 / Issue 4 / April 2015
Print publication: April 2015
Following Jacquet, Lapid and Rogawski, we define a regularized period of an automorphic form on $\text{GL}_{n+1}\times \text{GL}_{n}$ along the diagonal subgroup $\text{GL}_{n}$ and express it in terms of the Rankin–Selberg integral of Jacquet, Piatetski-Shapiro and Shalika. This extends the theory of Rankin–Selberg integrals to all automorphic forms on $\text{GL}_{n+1}\times \text{GL}_{n}$ .
Wideband, high-efficiency, high-power GaN amplifiers, using MIC and quasi-MMIC technologies, in the 1–4 GHz range
Chamssedine Berrached, Diane Bouw, Marc Camiade, Kassem El-Akhdar, Denis Barataud, Guillaume Neveux
Journal: International Journal of Microwave and Wireless Technologies / Volume 7 / Issue 1 / February 2015
Published online by Cambridge University Press: 09 June 2014, pp. 1-12
In this paper, the designs and experimental performances of wideband (higher than one octave) high-efficiency, high-power amplifiers (HPA) working in the 1–4 GHz range, using the same GaN process, are presented. They are based on the Bode–Fano integrals, which can be applied to a trade-off calculation between bandwidth and efficiency. Firstly, an microwave intregrated circuits (MIC) wideband HPA, externally matched, is presented. It generates a continuous wave (CW) output power (Pout) greater than 40 W, a power gain (GP) higher than 9.2 dB and a corresponding power added efficiency (PAE) (drain efficiency (DE)) ranged between 36 and 44% (40 and 48%) over the 1–3 GHz bandwidth. Two other amplifiers have been designed upon the same theoretical methodology, with a passive GaAs MMIC circuit technology, enabling to reduce the final size down to 420 mm2. The first internally matched Quasi monolithic microwave intergrated circuits (Quasi-MMIC) single-ended HPA generates a pulsed Pout greater than 25 W, GP higher than 9.8 dB, and a corresponding PAE (DE) ranged between 37 and 52.5% (40 and 55%) over the 2–4 GHz bandwidth. The second internally matched Quasi-MMIC HPA, based on balanced architecture, generates a pulsed Pout higher than 45 W, GP higher than 9.5 dB and PAE (DE) ranged between 33 and 44% (38 and 50%) over the 2–4 GHz bandwidth. These results are among the best ones published in terms of PAE and Pout in instantaneous octave bandwidth in the 1–4 GHz frequency range.
Evaluation of GaN-HEMT power amplifiers using BST-based components for load modulation
Mhd. Tareq Arnous, Alex Wiens, Paul Saad, Sebastian Preis, Zihui Zhang, Rolf Jakoby, Georg Boeck
In this paper, the concept of load-modulated power amplifiers (PAs) is studied. Two GaN-HEMT power amplifiers (PAs), targeted for high efficiency at maximum and output back-off (OBO) power levels, are designed, implemented, and tested across 1.8–2.2 GHz. The load modulation in the first design is realized by tuning the shunt capacitors in the output matching network. A novel method is employed in the second design, where barium–stronrium–titante is used for the realization of load modulation. The large-signal measurement results across the desired band show 59–70% drain efficiency at 44–44.5 dBm output power for both designs. Using the available tunable technique, the drain efficiency of the PAs is enhanced by 4–20% at 6 dB OBO across the bandwidth.
Structural and Chemical Evolution of the Spontaneous Core-Shell Structures of Al x Ga1-x N/GaN Nanowires
Rabie Fath Allah, Teresa Ben, David González
Journal: Microscopy and Microanalysis / Volume 20 / Issue 4 / August 2014
Published online by Cambridge University Press: 03 April 2014, pp. 1254-1261
A study by electron microscopy techniques of the structural and compositional properties of Al x Ga1-x N/GaN nanowire (NW) heterostructures on Si(111) is presented. Al x Ga1-x N depositions grown without catalyst by plasma-assisted molecular beam epitaxy were designed to form NWs in the range of 0.20<x<0.40 with different lengths and growth temperatures. The NWs exhibit a well-defined core-shell radial structure with a complex chemical distribution along and across the growth direction that finally affects the NW morphology. All the wires have an initial stage with a maximum Al content in the core slightly above the GaN/Al x Ga1-x N interface, which initially decreases exponentially with the NW height depending on the nominal Al content and the growth temperature. In longer NWs, this trend changes and evolves increasing both the Al/Ga ratio and the core diameter as well as sharpening the shell. Adatom surface kinetic differences and the geometrical shadow effect during the growth are the probable drivers of this behavior.