Papers by Keyword: GaN

Abstract: In this paper, the radiation resistance of GaN and SiC is compared. The effect of the irradiation temperature on the carrier removal rate in both semiconductors during proton irradiation is considered. It was found that in GaN, as well as in SiC, the rate of carrier removal decreases with increasing irradiation temperature. The dependence of the GaN sample resistance on the radiation dose was also calculated based on a model previously proposed to describe a similar dependence for SiC. Based on the experimental data obtained, it is concluded that the processes of radiation compensation in GaN and SiC are similar.

Abstract: The electronic structure of ultrathin Na/GaN interfaces was studied using photoelectron spectroscopy with synchrotron radiation in the photon energy range of 75–770 eV. The experiments were carried out in situ in ultrahigh vacuum of 5·10^–10 Torr with submonolayer sodium coverages on the gallium nitride surface. The photoemission spectra of the Ga 3d and N 1s core levels were studied at different excitation energies. It was found that Na adsorption causes a decrease in the intensity and a shift in the spectra of the Ga 3d and N 1s core levels towards higher binding energies. It was found that the sodium adsorption leads to some changes in the spectra due to charge transfer between the Na adlayer and the surface Ga or N atoms.

Abstract: Subsurface photoacoustic imaging with high resolution is utilized to image the teeth layer due to periodontal tissue inflammation. The aim of this imaging method is to determine the difference between healthy teeth and teeth affected by inflammation based on the acoustic signals obtained. An 808 nm diode laser is used as a radiation source, a condenser microphone is used as a detector, and computer numerical control (CNC) is used for the sample scanning process. The samples were healthy and inflamed Sprague-Dawley rat teeth. The average acoustic intensity of healthy teeth layers was 60.200.9 dB for enamel and 52.210.9 dB for dentin, while the average acoustic intensity of inflammation-affected teeth layers was 93.140.4 dB for enamel and 84.840.4 dB for dentin. Based on the histogram results obtained, the generative adversarial network (GAN) method can be used to improve photoacoustic image resolution to become more detailed. The study shows that high-resolution subsurface photoacoustic imaging can be utilized to image teeth layers.

Abstract: This work explores the application of gallium nitride (GaN)-based solid-state devices for high-power, high-frequency, and high-temperature technologies. It presents an in-depth study of GaN on semi-insulating SiC substrates. The study demonstrates, through bow range investigation, optical microscopy, and X-ray diffraction (XRD), that by adapting growth parameters from those used for Si substrates to those suitable for SiC substrates, it is possible to achieve high-quality crystalline MOCVD growth both under on-axis and 4°off-axis substrate orientations.

Abstract: GaN power HEMTs enable the design of power electronic systems with highest efficiencies and reduced size. Despite strong advancements in device reliability, charge carrier trapping is still an important challenge. The applied methodology allows to characterize defects that cause the dynamic R_DS,on in GaN power devices at product level with flexibility in duty cycle, number of pulses and mission profile. A pronounced trapping is observed for lateral GaN-on-Si HEMTs with Schottky p-GaN gate structure at low drain bias and long off-state pulses (> 100 ms). The effect is investigated by fast determination of the on-state resistance R_DS,on under different trap capturing conditions: a) different drain bias b) off-state time and number of cycles c) variation of temperature. The trapping and detrapping effects are characterized and the activation energy is extracted from time constants. An elevated on-state resistance was present for up to 3 hours. The threshold voltage modification due to high drain bias does explain the significant R_DS,on increase.

Abstract: Understanding heat transfer phenomena is crucial in high-power amplifiers to keep components within safe operating temperatures. This article investigates the GaN Power Amplifier (PA) thermal analysis for the optimum design of the heatsink. GaN PAs are roughly separated into junction, package, and heat sink layers to calculate the junction’s transient thermal response. It has been proven that allowing individual components to operate at temperatures over their maximum rated junction temperatures significantly reduces the system's operational reliability as a whole. This analysis investigates two different heat sinks for the optimum case temperature (T_case) for these different PAs. These PAs are operating S-band (2-3.4 GHz) and C-Ku-band (5-18 GHz) with drain efficiency of 60-65% and 9-22%, respectively. The design analysis of the heat sink for optimal performance is explored in this work.

Abstract: GaN-based nanopillar crystals are directly grown on multicrystalline Si and amorphous-carbon-coated graphite substrates whose surfaces are not mirror-polished. Light-emitting diodes (LEDs) of a double-hetero structure are prepared from the nanopillar crystals, and their optical–emission properties are investigated. Despite the substrate type and surface conditions, moderate light emissions are obtained from nanopillar LEDs though the light emissions are not always homogeneous, especially in the LEDs prepared on the graphite-based substrate. Nevertheless, these results will lead to realizations of novel large-area light-emitting devices.

Abstract: With the increasing use of III-nitride semiconductors, more knowledge is needed about the manufacturing processes and reactions with different chemicals. Gallium nitride semiconductors show a different behavior in wet chemistry compared to the known silicon technologies [4,5]. The different behavior can be explained, among other things, by the polar axis in the c-direction [0001] [6]. Surface characterization is necessary to gain a better understanding of the native surface and after different processes. We have used Low Energy Ion Scattering (LEIS) with its very high sensitivity for surface characterization to characterize the surface of different gallium nitride semiconductors and to establish a depth profile by sputtering [1,8].

Abstract: The new laser ablation technique has been developed for analysis of metallic impurities in SiC and GaN wafers. Particles generated by a femto-second laser ablation were aspirated by an ejector and introduced to an Inductively Coupled Plasma Mass Spectrometry (ICP-MS) via a Gas Exchange Device (GED) and analyzed. A Metal Standard Aerosol Generation (MSAG) was used for quantitation of metallic impurities in SiC and GaN wafers.

Abstract: Gold nanoparticles (AuNPs) is known for its high surface area to volume ratio which acts as an excellent receptor when placed in between electrodes in sensors application. Microelectrodes which are bar and needle shape pointed ends with two arrangements; comb and castle wall configurations were designed to be used for fabrication of electrodes to observe the relation between geometry of electrodes and dielectrophoretic of AuNPs on p-gallium nitride (GaN) substrates. The dielectrophoretic behaviour and electrical properties were analysed before and after the drop cast of AuNPs using current-voltage (I-V) curve method with manual probing. Resistance values of each sample were calculated under reverse bias condition. The effect of design on the nanomanipulation of AuNPs will be discussed.