Barrier Thickness Research Articles

Study of the Interface and Radial Dopant Position in Semiconductor Heterostructures Using X-ray Absorption Spectroscopy.

Two questions that remain a challenge in the field of colloidal doped core/shell nanomaterials of different morphologies are the nature of the interface and the radial location of the dopant ion due to the diffusion within the lattice. Using a model system of Cu-doped CdSe/CdS quantum dots, we develop an in-depth understanding of the extended X-ray absorption fine structure (EXAFS) spectra of the dopant and host atoms to address both issues. Our findings suggest that the interface is not sharp, in agreement with the nonstructural studies in the literature. Local structure analysis around the Cu dopant ion confirms that Cu drifts out from the core toward the outer region in the absence of the shell but stays mostly in the core after the formation of a sufficiently thick interfacial barrier (∼2 monolayers). This study highlights the significance of EXAFS spectroscopy in understanding the nature of the interface in nanomaterials.

Energy band offsets and charge transport process in an InAsSb based nBn structure: A numerical simulation

We report on the valence energy band offset (ΔEvC-A) between the InAsSb contact (C) and the InAsSb absorber (A) layers, in the C–InAsSb/B–AlAsSb/A-InAsSb nBn structure. ΔEv(C-A) is analyzed, numerically, for different thicknesses of the AlAsSb barrier (B) layer and different doping levels of the barrier and the contact layers, under equilibrium and at room temperature. A value of ΔEv(C-A) around 0,331 meV, corresponding to a near flat band situation, was obtained with donor's concentration of about 1016 cm−3 in the contact. First, simulations were carried at room temperature, under reverse bias, and for a 50 nm and a 100 nm barrier's thicknesses. The temperature dependence of ΔEv(C-A), under reverse bias, was analyzed between 150 K and 300 K. Finally, the reverse current-voltage characteristics of the structure were simulated in the dark and under illumination. Our results are compared to experimental results encountered in the literature and for the same system.

Oblique Wave Diffraction by a Bottom-Standing Thick Barrier and a Pair of Partially Immersed Barriers

Abstract On the basis of the linearized theory of water waves, the present study has demonstrated a semi-analytical method to assess the hydrodynamic performance of a pair of partially immersed barriers just above a thick bottom-standing barrier. By means of the eigenfunction expansion method, a system of the first kind Fredholm-type integral equation involving a horizontal component of velocity as unknown functions is developed for the interaction of water waves with both types of barriers. The multiterm Galerkin approximation is adopted to determine these unknown functions having square root singularities at the submerged edge of the thin barriers and one-third singularities at the corners of the thick barrier. In order to overcome such types of singularities, Chebychev polynomials for half-singularities and ultra-spherical Gegenbauer polynomials for one-third singularities with suitable weight functions have been taken into consideration. The numerical examples of both reflection and transmission coefficients are presented to examine the hydrodynamic performance of breakwater. Some fascinating results like resonant frequencies are obtained for practical engineering. At the same time, reflection coefficients for the present breakwater agree reasonably for the limiting cases with the previously available results.

Fabrication and characterization of NbN/(TaN/NbN) N stacked Josephson junctions

In this work, we present a detailed study of the electrical properties of stacked NbN/(TaN/NbN) N Josephson junctions. Cross-sectional scanning transmission electron microscopy analysis of the 5-stacked junction shows that the multilayer interface is very flat, each barrier has the same thickness, and the sidewalls of the junctions are nearly perpendicular to the substrate. Stacked junctions of different sizes and stacking numbers all have only one transition in their current–voltage curves. This indicates that the critical currents of the junctions in the stacked junctions are almost the same, showing the stability and repeatability of the multilayer fabrication and etching process. At 4.2 K, the 4-stacked junction shows excellent Josephson properties with characteristic voltage V c of 3.54 mV, which is about four times the 0.88 mV of the single junction. The temperature dependence of critical current density J c and V c of the stacked junction with N = 1, 2, 4 were measured, all of which can be fitted with dirty-limit theory. Stacked junctions with larger V c or more stacked layers can be achieved by optimizing electrode and barrier thickness, barrier resistivity, and thermal relaxation rate, etc.

Tunneling Spectroscopy of Two-Dimensional Materials Based on Via Contacts.

We introduce a novel planar tunneling architecture for van der Waals heterostructures based on via contacts, namely, metallic contacts embedded into through-holes in hexagonal boron nitride (hBN). We use the via-based tunneling method to study the single-particle density of states of two different two-dimensional (2D) materials, NbSe2 and graphene. In NbSe2 devices, we characterize the barrier strength and interface disorder for barrier thicknesses of 0, 1, and 2 layers of hBN and study the dependence on the tunnel-contact area down to (44 ± 14)2 nm2. For 0-layer hBN devices, we demonstrate a crossover from diffusive to point contacts in the small-contact-area limit. In graphene, we show that reducing the tunnel barrier thickness and area can suppress effects due to phonon-assisted tunneling and defects in the hBN barrier. This via-based architecture overcomes limitations of other planar tunneling designs and produces high-quality, ultraclean tunneling structures from a variety of 2D materials.

Microelectronic current-sourcing device based on band-to-band tunneling current

A new stable current-sourcing transistor is developed using the band-to-band tunneling phenomenon. A heterojunction between thin film WS2 and heavily hole-doped bulk silicon converts a section of the WS2 contacting the silicon into a hole-doped WS2 inside the WS2 channel, and band-to-band tunneling occurs between the electron-doped and hole-doped WS2. The output current is regulated by the tunneling barrier thickness. The thickness depends on the gate bias for device switching, but is less sensitive to the source bias, enabling stable output currents. The minimum line sensitivity is 2.6%, and the temperature coefficient is 1.4 × 103 ppm °C−1. The device can be operated as a current sourcing device with an ultralow output current and power consumption.

Growth behavior and morphology of sidewall intermetallic compounds in Cu/Ni/sn-Ag microbumps during multiple reflows

Sidewall intermetallic compounds (IMCs) grow rapidly by surface diffusion with the bump size shrinking. Cu/Ni/sn-Ag microbumps with thick Ni barrier have been fabricated and the inhibition effect of thick Ni barrier on sidewall IMCs growth during multiple reflows was investigated. Three kinds of sidewall IMCs were found: Ni3Sn4 (main product), Ni3Sn2 and Cu3Sn. The growth kinetics of sidewall Ni3Sn4 showed that the formation of Ni3Sn4 contained two stages: at first, sidewall Ni3Sn4 grew rapidly due to reactive wetting of molten solder; subsequently, the formation slowed down since the solder wetting was blocked by continuous Ni3Sn4 layer, and Ni3Sn2 and Cu3Sn formed by surface diffusion of Sn atoms.

Engineering pedicled vascularized bladder tissue for functional bladder defect repair.

An engineered bladder construct that mimics the structural and functional characteristics of native bladder is a promising therapeutic option for bladder substitution. We previously showed that pedicled vascularized smooth muscle tissue fabricated by grafting smooth muscle cell (SMC) sheets onto an axial capsule vascular bed had the potential for reliable bladder reconstruction. In this study, we investigated the feasibility of buccal mucosa graft (BMG) integration with the pedicled vascularized smooth muscle tissue to generate a full-layer pedicled vascularized bladder construct. BMG transplanted onto vascularized smooth muscle tissue showed good survival and developed into a pedicled vascularized bladder construct with full-layer structures, appropriate thickness, abundant vascularization, and effective barrier function. Then the full-thickness bladder defects were, respectively, reconstructed by pedicled capsule tissue (pedicled capsule group), nonpedicled vascularized bladder construct (nonpedicled construct group), and pedicled vascularized bladder construct (pedicled construct group). The picrosirius red (PSR) staining and immunohistochemistry results showed minimal fibrosis, maximal smooth muscle proportion, and high vascular density in the pedicled construct group. A continuous mucosal layer was observed only in the pedicled construct group. Moreover, morphological and functional studies revealed better bladder compliance and good ductility in the pedicled construct group. Overall, these results suggested that the BMG could be well integrated with vascularized smooth muscle tissue and generated a pedicled, fully vascularized, and structurally organized bladder construct, which facilitated structural remodeling and functional recovery and could become an alternative to bladder reconstruction.

Hydrophilic Composites of Chitosan with Almond Gum: Characterization and Mechanical, and Antimicrobial Activity for Compostable Food Packaging.

To enhance the characteristics of the biocomposite film, solution cast was used to incorporate almond gum at different concentrations (10.0, 30.0, and 50.0%). The functional groups and morphology were determined using FTIR and SEM. The thermal property of chitosan and its composites materials were determined via TGA. In this study, the incorporation of almond gum into the chitosan matrix resulted in good mechanical strength, film thickness, and low barrier and solubility characteristics. Water vapor transmission rate (WVTR) and oxygen transmission rate (OTR) of the composites films was also investigated. The WVTR and OTR values for the chitosan/almond gum (CSA) composite film values are 11.6 ± 1.62 (g/m2/day) and 32.9 ± 1.95(cc/m2/24 h),respectively. The obtained composites show significantly improved antimicrobial activity against Gram-negative (E. coli) and Gram-positive (S. aureus) food-borne pathogenic bacteria. The results suggest that the CSA composites may serve as a promising candidate for antimicrobial food packaging materials. After an observation of the test results, it is inferred that the CSA composites bear good mechanical and antimicrobial activity and also show enhanced morphological characteristics.

USING N-OVEL COATED SAND AS REACTIVE BED IN PERMEABLE BARRIER FOR ELIMINATION OF METHYL ORANGE DYE FROM GROUNDWATER*

This study investigates the efficacy of sand coated with calcium / aluminum (Ca/Al)-layered double hydroxide (LDH) in the elimination of methyl orange dye from simulated groundwater using method of permeable reactive barrier. For green (sustainable) manufacturing of this sand, aluminum prepared from dissolution of alum (cheap coagulant) can be interacted chemically with calcium extracted from cement kiln dust byproduct to create nanoparticles of Ca and Al that precipitate on the filter sand. Sorption measurements for interaction of methyl orange dye and coated sand was well formulated by Langmuir model with highest value of correlation (determination coefficient= 0.999) and lowest errors (sum of squared errors= 0.0122). Also, the maximum capacity of adsorption was valued of 0.9453 mg/g and the sorption curve can classify as “favorable” type. According to desorption measurements, little percentage of dye (0.91%) can desorb from exhausted coated sand through washing with water due to strength of bonding between sorbent and dye molecules. Also, the exhausted sorbent can regenerate with efficiency not less than 85% after eight of regeneration cycles. Finally, measurements of breakthrough curves in the continuous mode operation using column setup proved that the propagation of dye front (and consequently the longevity of barrier) would increase significantly with thicker barrier and lowest values of influent concentration and flow rate. COMSOL (computer solution) package can use effectively in the simulation of these curves.

Varactor diodes of hydrogenated nanocrystalline Si with hydrogenated amorphous SiC prepared by PECVD

Hetero-structural barrier varactor diodes (HBVDs) can be widely used as variable capacitors, frequency multipliers, parametric amplifiers, etc. in electronic systems. Herein, n-type hydrogenated nano-crystalline Si (n-nc-Si:H) films with narrow band-gap and un-intentional doped hydrogenated amorphous SiC (a-SiC:H) ones with wide band-gap are adopted to innovatively design the n-nc-Si:H/a-SiC:H/n-nc-Si:H-based HBVDs. Two periodic hetero-structures with different doped nc-Si:H modulation layers and different thickness a-SiC:H barriers are severally fabricated by plasma enhanced chemical vapor deposition (PECVD), the optical band-gaps of n-nc-Si:H and a-SiC:H are derived from the ultra violet-visible (UV–vis) absorption spectra, the prepared devices are demonstrated as the HBVDs by measuring the relations of current density–voltage and capacitance–voltage, respectively. The conduction mechanisms of the fabricated devices in different biased voltage ranges are probed, the variation of capacitance modulation ratio with changing the doped-level in modulation layers and thickness of barriers are analyzed. This paper will be helpful to extend the material combination and preparation method for HBVDs.

Interface Engineering Enabled Low Temperature Growth of Magnetic Insulator on Topological Insulator

AbstractCombining topological insulators (TIs) and magnetic materials in heterostructures is crucial for advancing spin‐based electronics. Magnetic insulators (MIs) can be deposited on TIs using the spin‐spray process, which is a unique nonvacuum, low‐temperature growth process. TIs have highly reactive surfaces that oxidize upon exposure to atmosphere, making it challenging to grow spin‐spray ferrites on TIs. In this work, it is demonstrated that a thin titanium capping layer on TI, followed by oxidation in atmosphere to produce a thin TiOx interfacial layer, protects the TI surface, without significantly compromising spin transport from the magnetic material across the TiOx to the TI surface states. First, it is demonstrated that in Bi2Te3/TiOx/Ni80Fe20 heterostructures, TiOx provides an excellent barrier against diffusion of magnetic species, yet maintains a large spin‐pumping effect. Second, the TiOx is also used as a protective capping layer on Bi2Te3, followed by the spin‐spray growth of the MI, NixZnyFe2O4 (NZFO). For the thinnest TiOx barriers, Bi2Te3/TiOx/NZFO samples have antiferromagnetic (AFM) disordered interfacial layer because of diffusion. With increasing TiOx barrier thickness, the diffusion is reduced, but still maintains strong interfacial magnetic exchange‐interaction. These experimental results demonstrate a novel method of low‐temperature growth of magnetic insulators on TIs enabled by interface engineering.

Condensed-phase isomerization through tunnelling gateways

Quantum mechanical tunnelling describes transmission of matter waves through a barrier with height larger than the energy of the wave1. Tunnelling becomes important when the de Broglie wavelength of the particle exceeds the barrier thickness; because wavelength increases with decreasing mass, lighter particles tunnel more efficiently than heavier ones. However, there exist examples in condensed-phase chemistry where increasing mass leads to increased tunnelling rates2. In contrast to the textbook approach, which considers transitions between continuum states, condensed-phase reactions involve transitions between bound states of reactants and products. Here this conceptual distinction is highlighted by experimental measurements of isotopologue-specific tunnelling rates for CO rotational isomerization at an NaCl surface3,4, showing nonmonotonic mass dependence. A quantum rate theory of isomerization is developed wherein transitions between sub-barrier reactant and product states occur through interaction with the environment. Tunnelling is fastest for specific pairs of states (gateways), the quantum mechanical details of which lead to enhanced cross-barrier coupling; the energies of these gateways arise nonsystematically, giving an erratic mass dependence. Gateways also accelerate ground-state isomerization, acting as leaky holes through the reaction barrier. This simple model provides a way to account for tunnelling in condensed-phase chemistry, and indicates that heavy-atom tunnelling may be more important than typically assumed.

Investigation of back barrier material effects on the scalability of Fe-doped recess-gated AlN/GaN HEMTs for next generation RF power electronics

GaN HEMTs (high-electron-mobility transistors) on SiC (silicon carbide) wafer with back barrier structures have gained much attention owing to the improved sheet charge density through enhanced carrier confinement, which can accomplish further improvement of RF performance. In this simulation work, the influence of different back barrier materials on RF & DC performance of Fe-doped recess gated AlN/GaN HEMT is explored. This paper also investigates the back barrier thickness effects on carrier confinement of each structure; the results show that better confinement of carriers in the GaN channel is accompanied by an optimized thickness for each back barrier material besides which, the performance is comparatively degraded. As back-barrier based structures have the capability to reduce SCEs by enhancing the carrier confinement, the investigation is done to analyse the impact of gate length scalability on the DC & RF characteristics of the proposed device. Lg = 60 nm Fe-doped recess-gated AlN/GaN HEMT with an optimized AlGaN back barrier thickness of 60 nm provided a peak drain current of 4.63 A/mm, the highest transconductance of 2333 mS/mm, and the highest cut-off frequency of 316.6 GHz, and this outstanding DC/RF performance is due to strong carrier confinement and reduced leakage current. This outstanding performance makes them a potential choice for future RF power electronics and MMIC design.

Evolution of Reverse‐Biased Current of a Barristor Junction by Varying Temperature and Barrier Height of the Junction

AbstractThe reverse‐biased current of a Schottky junction comprises the thermionic emission current and the Fowler–Nordheim tunneling current, depending on the barrier height and thickness. Because both are fixed at traditional Schottky junctions, so is the current mechanism. However, a barristor junction has a tunable barrier height and the current mechanism changes accordingly. Here, the evolution of the current mechanism of the graphene–WS2 junction is investigated by varying the gate voltage, drain voltage, and temperature. As the height decreases with the accumulation of electrons on graphene, the dominant transport mechanism of the junction changes from thermionic to field emission. As the temperature increases, the extrinsic carrier concentration of WS2 increases and thus the thickness decreases, resulting in the same evolution. In addition, a kink in the ID–VD curves over a specific range of gate voltages and temperatures is observed. This may originate from the alignment of the Fermi level of graphene to the Dirac point, which dramatically reduces the Fowler–Nordheim tunneling current.

Thick thermal barrier coatings with different segmentation crack densities: Microstructure analysis and thermal oxidation behavior

Thick thermal barrier coatings (TTBCs) have been developed to increase the lifetime of hot section parts in gas turbines by increasing the thermal insulating function. The premeditated forming of segmentation cracks was found to be a valuable way for such an aim without adding a new layer. The TTBC introduced in the current study are coatings with nominal thickness ranging from 1 to 1.1 consisting of MCrAlY bond coat and 8YSZ top coat deposited by air plasma spray technique (APS). TTBCs with segmented crack densities of 0.65 mm−1 (type-A) and 1 mm−1 (type-B) were deposited on a superalloy substrate by adjusting the coating conditions. It was found that the substrate temperature has an influential role in creating the segmentation crack density. The crack density was found to increase with substrate temperature and liquid splat temperature. The two types of coatings (type-A and B) with different densities of segmentation crack were heat-treated at 1000 °C (up to 100 h) and 1100 °C (up to 500 h). The variation of hardness measured by indentation testing indicates a similar trend in both types of coatings after heat treatments at 1000 °C and 1100 °C. Weibull analysis of results demonstrates that higher preheating coating during the deposition results in a denser YSZ coating. The growth rate of TGO for TTBCs was evaluated for cyclic and isothermal oxidation routes at 1000 °C and 1100 °C. The TGO shows the parabolic trend for both two types of coatings. The Kps value for two oxidation types is between 5.84 × 10−17 m2/s and 6.81 × 10−17 m2/s. Besides, the type B coating endures a lifetime of more than 40 cycles at thermal cycling at 1000 °C.

Crystallization and stability of rare earth iron garnet/Pt/gadolinium gallium garnet heterostructures on Si

The crystallization of rare earth iron garnet films such as dysprosium iron garnet on Si substrates provides a path for integration of these complex oxides into magnetic devices. We report the growth of 50–75 nm thick dysprosium yttrium iron garnet (YDyIG) films, deposited without a seed layer then crystallized by a 750 °C rapid thermal anneal, forming a polycrystalline film with grains of several µm diameter containing radiating low-angle boundaries. The Y:Dy ratio affects the magnetization and anisotropy of YDyIG. Crystallization becomes more challenging as the garnet film thickness decreases. To crystallize thinner rare earth garnet films, tri-layer stacks consisting of a 50 nm thick gadolinium gallium garnet (GGG) seed layer, a 1.5 nm thick Pt diffusion barrier, and a 10 nm thick YDyIG film were prepared. The YDyIG/Pt/GGG tri-layers showed agglomeration of the Pt leading to a morphology consisting of a polycrystalline garnet film enriched with Dy and Fe and containing a layer of Pt nanoparticles embedded near its surface.

(Digital Presentation) Negative Bias Illumination Stress on a-Igzo TFT with a Top Barrier

The double-layer a-IGZO thin film transistors (DL-TFTs) using a quantum well channel and a top barrier can improve not only the electrical properties and the positive bias temperature instability as compared to the single-layer TFT (SL-TFTs) [1][2] but also the negative bias illumination stress (NBIS). In this work, DL-TFTs have less negative VT shifts than that of SL-TFTs under NBIS. Moreover, the negative VT shift of DL-TFTs decreases with increasing top barrier thickness due to the energy barrier formed by the valence band discontinuity at the interface between the channel layer and the top barrier. Experimental Process: The 100 nm Mo/Al layers were first deposited on a glass substrate and patterned to form the bottom gate (BG) metal, followed by the deposition of 320 nm thick SiNx/SiOx gate insulator (GI) using plasma-enhanced chemical vapor deposition (PECVD). For the active layer of SL-TFT, 15 nm a-IGZO with high indium content was deposited to form a high mobility channel (HM-IGZO) using radio frequency magnetron sputtering with Ar plasma. As for the DL-TFTs, an extra standard a-IGZO (STD-IGZO, the atomic composition of the target is In2O3:Ga2O3:ZnO=1:1:2 mol%) was deposited as a top barrier. Two different top barrier thicknesses were deposited (10 nm and 30 nm) to investigate the thickness effect on the NBIS. The active layer was then patterned by photolithography. A 260 nm Ti was deposited and patterned by photolithography and reactive ion etch (RIE) as the S/D metal, followed by SiOx/SiNx top gate insulator deposition and the transparent indium tin oxide (ITO) top gate (TG) metal formation. To conduct the NBIS test, -30 V and 0 V were applied to the bottom gate and the top gate, respectively, and a light source with a wavelength of 365 nm was used as the illumination stress. Additional 100 nm films of HM and STD IGZO were deposited to investigate the band alignment. The bandgap (Eg), valence band offsets (EF-EV, where EF is the Fermi level and EV is the valence band edge), and work function can be extracted by Tauc method, X-Ray photoelectron spectroscopy (XPS), and Kelvin probe force microscopy (KPFM), respectively, to obtain the band alignment of the HM (channel layer) and the STD (top barrier) IGZO [3]. Results and Discussions: The evolution of VT shifts under NBIS are shown in Fig. 1. DL-TFTs have less VT shift than that of SL-TFT. Since the energy of the photon (3.4 eV) is larger than the bandgap of the a-IGZO (~3 eV), electron-hole pairs are generated by the light source. Since a negative voltage is applied to the BG, the generated holes are trapped into the BG GI, resulting in the negative VT shift. In DL-TFTs, the holes generated in the top barrier cannot be trapped into the BG GI due to the energy barrier formed by the valence band discontinuity. With the band alignment analysis [1], the valence band discontinuity is found to be 0.39 eV, which is high enough to stop the holes generated in the top barrier from trapping into the BG GI. The electrons generated in the top barrier can still be trapped into the TG GI, compensating the negative VT shift (Fig. 2(a)), resulting in a smaller VT shift in DL-TFTs than that of SL-TFTs. Reportedly, the VT shift increases with increasing a-IGZO thickness in SL-TFTs [4]. However, the VT shift decreases with increasing top barrier thickness in DL-TFTs (Fig. 1). Although the generated electron-hole pairs in the top barrier increase with increasing top barrier thickness, the additional holes cannot be trapped into the BG GI due to the valence band discontinuity, while the additional electrons can easily be trapped into the TG GI, leading to more VT shift compensation and thus less negative VT shift in the DL-TFT (Fig. 2(b)). Conclusion: The DL-TFTs have less VT shift under NBIS as compared to SL-TFTs. The NBIS can be further improved by increasing the top barrier thickness. Acknowledgment: This work was supported in part by the Ministry of Science and Technology, Taiwan, under Grant MOST 110-2218-E-A49-013-MBK, Grant MOST 110-2218-E-002-030, and Grant MOST 110-2622-8-002-014, and in part by the Ministry of Education, Taiwan, under Grant NTU-CC-110L892601. Reference: [1] J.-C. Chiu et al., J-EDS (2021) [2] J.-C. Chiu et al., IEDMS (2021) [3] A.-H. Tai et al., TED (2019) [4] M. M. Billah et al., EDL (2016) Figure 1

Investigation of Thin-Barrier AlGaN/GaN HEMT Heterostructures for Enhanced Gas-Sensing Performance

In this study, a theoretical relationship between two-dimensional electron gas (2DEG) properties of AlGaN/GaN high-electron-mobility transistor (HEMT) hetero- structure and various gas-sensing characteristics using this structure was established. Based on the analytical study, it is proposed that a thinner barrier layer in AlGaN/GaN HEMT heterostructure should result in lower detection limits, higher sensing response, and a faster response time. To prove the analytical study, a thin-barrier (~8 nm) AlGaN/GaN HEMT structure was designed and grown to study its sensing characteristics. The results are compared with the thick-barrier (~18 nm) gas sensor structure. For the thin-barrier NO2 sensor, the sensing response increased by almost ten times when <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sf \Delta {I}$ </tex-math></inline-formula> was changed by more than 25%. The sensor also showed a faster response time of 10 s when compared to the thick barrier sensor. Similarly, the thin-barrier NH3 sensor showed a remarkable improvement in sensing response by 17 times and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sf \Delta {I}$ </tex-math></inline-formula> by two times. Based on the response time, the thin-barrier NH3 sensor was also found to be 40% more faster compared to the thick-barrier AlGaN/GaN HEMT sensor.

A novel E-mode GaN p-MOSFET featuring charge storage layer with high current density

In this work, a trench gate enhancement-mode GaN p-type metal oxide semiconductor field effect transistor featuring charge storage (CS) layer is proposed, which exhibits an effectively improved current density. Based on device simulations, the current density can be increased by 154% (@V DS = −5 V, V GS = −7 V) compared with conventional devices without CS layer. Besides, the impact of the critical parameters including AlGaN barrier thickness t, Al mole-fraction x, trench gate depth T recess, and negative charge concentration N CSL on device performance are studied and optimized. In this case, the p-MOSFETs show an on-current |I ON, max| of 14 mA mm−1, V TH of −0.47 V, I ON /I OFF of >108, and on-resistance R ON of 0.27 kΩ mm. The proposed GaN p-MOSFETs exhibit a promising method to improve the current drive capability of GaN p-channel devices.