A hybrid approach for obtaining normally off high electron mobility transistors (HEMTs) combining fluorine treatment, recess etch techniques, and AlGaN buffer was studied. The effects of process variations (recess etch depth and fluorine treatment duration) and epitaxial differences (AlGaN and carbon doped GaN buffers) on the DC characteristics of the normally off HEMTs were investigated. Two different epitaxial structures and three different process variations were compared. Epitaxial structures prepared with an AlGaN buffer showed a higher threshold voltage (V th = +3.59 V) than those prepared with a GaN buffer (V th = +1.85 V).
In this paper, we report an angstrom-thick atomic layer deposited (ALD) aluminum oxide (Al 2 O 3) dielectric passivation layer for an AlGaN/GaN high electron mobility transistor (HEMT). Our results show a 55% improvement in the gate lag performance of the design and a decrease by half in interface state density upon coating with two cycles of ALD Al 2 O 3. DC characteristics such as current density, threshold voltage, and leakage currents were maintained. ALD Al 2 O 3 passivation layers with thicknesses up to 10 nm were investigated. XPS analyses reveal that the first ALD cycles are sufficient to passivate GaN surface traps. This study demonstrates that efficient passivation can be achieved in atomic-scale with dimensions much thinner than commonly used bulk layers.
We demonstrate the electrical performances of an AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor (MIS-HEMT) with low gate leakage current (I g ). A low gate leakage current as low as the order of 10 −11 A/mm was achieved from normally-off MIS-HEMT device (V th = 2.16 V) with a partially recessed gate, fluorine treatment, and ALD Al 2 O 3 gate dielectric layer. The gate leakage current decrease is attributed to the pre-treatment of the gate region with hydrofluoric acid (HF) and deionized water (DI) solution, which acts to remove the native oxide layer and thus decrease interface traps. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) analyses demonstrate that the AlGaN surfaces are modified such that the surface roughness and native oxide introduced by the treatments used to achieve normally-off operation are remedied with the use of the pre-treatment.
A normally-off InAlN/GaN high electron mobility transistor (HEMT) on Si substrate with a p-GaN gate is reported. Devices are fabricated on two different epitaxial structures, one containing a high resistive GaN buffer layer and one containing an AlGaN back-barrier, and the threshold voltage, drain current density, and buffer leakage current are compared. With the epitaxial structure containing a high resistive GaN layer, normally-off operation with a threshold voltage of +0.5 V is achieved. The threshold voltage is further increased to +2 V with the AlGaN back-barrier, and the buffer leakage current was improved by over an order of magnitude.
Typical surface-enhanced Raman scattering (SERS) approaches rely on localized surface plasmon resonances that provide a significant enhancement of the localized electric field. Unfortunately, this technique faces challenges in terms of repeatability, which appears due to the strong dependence of the field enhancement on the surface roughness and the presence of hot-spots in nanostructures; and adequate excitation, as the laser beam must be tuned at a very specific wavelength that corresponds to the resonant frequency of the system. Hyperbolic metamaterials (HMTMs), a type of composite materials whose effective permittivity changes as a function of the electric field polarization, can effectively address these challenges because they support bulk and surface hyperbolic modes able to drastically boost the local fields over a broadband portion of the electromagnetic spectrum. In fact, the frequency response of these artificial materials can be manipulated by adjusting the system composing materials and filling ratios. This work aims to explore the potential of HMTMs to enhance the SERS of molecules located nearby and to address some of the challenges faced by common SERS platforms. To this purpose, we focus on Au/SiO2 HMTMs stacks that exhibit a hyperbolic dispersion for wavelengths larger than ~580 nm. A prototype has been fabricated and characterized using TEM and ellipsometry measurements. Power-dependent SERS measurements were obtained for a monolayer of biphenyl-4,4’-dithiol (BPDT) molecules self-assembled onto the HMTM surface and a gold-based control sample. HMTMs provide repeatable SERS detection with low laser powers <900µW and integration times <97ms (~30X and ~100X lower than control, respectively) over a large surface area, exhibiting a performance like complex TERS systems.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.