An official website of the United States government
With rapid evolution of mobile core network (MCN) architectures, large-scale control-plane traffic (CPT) traces are critical to studying MCN design and performance optimization by the R&D community. The prior-art control-plane traffic generator SMM heavily relies on domain knowledge which requires re-design as the domain evolves. In this work, we study the feasibility of developing a high-fidelity MCN control plane traffic generator by leveraging generative ML models. We identify key challenges in synthesizing high-fidelity CPT including generic (to data-plane) requirements such as multimodality feature relationships and unique requirements such as stateful semantics and long-term (time-of-day) data variations. We show state-of-the-art, generative adversarial network (GAN)-based approaches shown to work well for data-plane traffic cannot meet these fidelity requirements of CPT, and develop a transformer-based model, CPT-GPT, that accurately captures complex dependencies among the samples in each traffic stream (control events by the same UE) without the need for GAN. Our evaluation of CPT-GPT on a large-scale control-plane traffic trace shows that (1) it does not rely on domain knowledge yet synthesizes control-plane traffic with comparable fidelity as SMM; (2) compared to the prior-art GAN-based approach, it reduces the fraction of streams that violate stateful semantics by two orders of magnitude, the max y-distance of sojourn time distributions of streams by 16.0%, and the transfer learning time in deriving new hourly models by 3.36×.
more »
« less
Intersubband Transitions in GaNZAl0.5Ga0.5N Quantum Wells on a-Plane and m-Plane GaN Substrates
We experimentally characterize mid-infrared intersubband transitions in identical Al0.5Ga0.5N/GaN heterostructures grown on a- and m-plane GaN substrates. The absorption peaks of the m-plane samples are 10 to 40% narrower than that of the a-plane samples.
more »
« less
- Award ID(s):
- 1810318
- PAR ID:
- 10277413
- Date Published:
- Journal Name:
- Conference on Lasers and Electro-Optics
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Significant effort for demonstrating a gallium nitride (GaN)-based ferroelectric metal–oxide–semiconductor (MOS)-high-electron-mobility transistor (HEMT) for reconfigurable operation via simple pulse operation has been hindered by the lack of suitable materials, gate structures, and intrinsic depolarization effects. In this study, we have demonstrated artificial synapses using a GaN-based MOS-HEMT integrated with an α-In2Se3 ferroelectric semiconductor. The van der Waals heterostructure of GaN/α-In2Se3 provides a potential to achieve high-frequency operation driven by a ferroelectrically coupled two-dimensional electron gas (2DEG). Moreover, the semiconducting α-In2Se3 features a steep subthreshold slope with a high ON/OFF ratio (∼1010). The self-aligned α-In2Se3 layer with the gate electrode suppresses the in-plane polarization while promoting the out-of-plane (OOP) polarization of α-In2Se3, resulting in a steep subthreshold slope (10 mV/dec) and creating a large hysteresis (2 V). Furthermore, based on the short-term plasticity (STP) characteristics of the fabricated ferroelectric HEMT, we demonstrated reservoir computing (RC) for image classification. We believe that the ferroelectric GaN/α-In2Se3 HEMT can provide a viable pathway toward ultrafast neuromorphic computing.more » « less
-
Understanding and characterizing the intrinsic properties of charge carrier transport across the interfaces in van der Waals heterostructures is critical to their applications in modern electronics, thermoelectrics, and optoelectronics. However, there are very few published cross-plane resistivity measurements of thin samples because these inherently 2-probe measurements must be corrected for contact and lead resistances. Here, we present a method to extract contact resistances and metal lead resistances by fitting the width dependence of the contact end voltages of top and bottom electrodes of different linewidths to a model based on current crowding. These contributions are then subtracted from the total 2-probe cross-plane resistance to obtain the cross-plane resistance of the material itself without needing multiple devices and/or etching steps. This approach was used to measure cross-plane resistivities of a (PbSe)1(VSe2)1 heterostructure containing alternating layers of PbSe and VSe2 with random in-plane rotational disorder. Several samples measured exhibited a 4 order of magnitude difference between cross-plane and in-plane resistivities over the 6–300 K temperature range. We also reported the first observation of charge density wave transition in the cross-plane transport of (PbSe)1(VSe2)1 heterostructure. The device fabrication process is fully lift-off compatible, and the method developed enables the straightforward measurement of the resistivity anisotropy of most thin film materials with nm thicknesses.more » « less
-
The structure and optical characteristics of thin (∼30 nm) wurtzite AlInN films grown pseudomorphic on free-standing, c-plane GaN substrates are presented. The Al1−xInxN layers are grown by metalorganic chemical vapor deposition, resulting in films with varying In content from x = 0.142 to 0.225. They are measured using atomic force microscopy, x-ray diffraction, reciprocal space mapping, and spectroscopic ellipsometry (SE). The pseudomorphic AlInN layers provide a set where optical properties can be determined without additional variability caused by lattice relaxation, a crucial need for designing devices. They have smooth surfaces (rms < 0.29 nm) with minimum pit areas when the In content is near lattice-matched to GaN. As expected, SE shows that the refractive index increases and the bandgap energy decreases with increased In-content. Plots of bandgap energy vs In content are fitted with a single bowing parameter of 3.19 eV when using bandgap energies for AlN and InN pseudomorphic to GaN, which is lower than previous measurements and closer to theoretical predictions.more » « less
-
Gallium nitride (GaN)-based high electron mobility transistors (HEMTs) are essential components in modern radio frequency power amplifiers. In order to improve both the device electrical and thermal performance (e.g., higher current density operation and better heat dissipation), researchers are introducing AlN into the GaN HEMT structure. The knowledge of thermal properties of the constituent layers, substrates, and interfaces is crucial for designing and optimizing GaN HEMTs that incorporate AlN into the device structure as the barrier layer, buffer layer, and/or the substrate material. This study employs a multi-frequency/spot-size time-domain thermoreflectance approach to measure the anisotropic thermal conductivity of (i) AlN and GaN epitaxial films, (ii) AlN and SiC substrates, and (iii) the thermal boundary conductance for GaN/AlN, AlN/SiC, and GaN/SiC interfaces (as a function of temperature) by characterizing GaN-on-SiC, GaN-on-AlN, and AlN-on-SiC epitaxial wafers. The thermal conductivity of both AlN and GaN films exhibits an anisotropy ratio of ∼1.3, where the in-plane thermal conductivity of a ∼1.35 μm thick high quality GaN layer (∼223 W m−1 K−1) is comparable to that of bulk GaN. A ∼1 μm thick AlN film grown by metalorganic chemical vapor deposition possesses a higher thermal conductivity than a thicker (∼1.4 μm) GaN film. The thermal boundary conductance values for a GaN/AlN interface (∼490 MW m-2 K−1) and AlN/SiC interface (∼470 MW m−2 K−1) are found to be higher than that of a GaN/SiC interface (∼305 MW m−2 K−1). This work provides thermophysical property data that are essential for optimizing the thermal design of AlN-incorporated GaN HEMT devices.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/https://doi.org/10.1364/CLEO_AT.2020.JTh2D.17vvv
