High Hole Density Research Articles

Modulation Doping via a Two-Dimensional Atomic Crystalline Acceptor.

Two-dimensional nanoelectronics, plasmonics, and emergent phases require clean and local charge control, calling for layered, crystalline acceptors or donors. Our Raman, photovoltage, and electrical conductance measurements combined with ab initio calculations establish the large work function and narrow bands of α-RuCl3 enable modulation doping of exfoliated single and bilayer graphene, chemical vapor deposition grown graphene and WSe2, and molecular beam epitaxy grown EuS. We further demonstrate proof of principle photovoltage devices, control via twist angle, and charge transfer through hexagonal boron nitride. Short-ranged lateral doping (≤65 nm) and high homogeneity are achieved in proximate materials with a single layer of α-RuCl3. This leads to the best-reported monolayer graphene mobilities (4900 cm2/(V s)) at these high hole densities (3 × 1013 cm-2) and yields larger charge transfer to bilayer graphene (6 × 1013 cm-2).

Coolant Jets Blowing Across the Airfoil Stagnation Line to Enhance Film Effectiveness

Abstract A novel airfoil leading edge film cooling design has been investigated, and its performance over conventional alternatives quantified. In conventional designs, the region near the geometric stagnation line is typically between the two most upstream film hole rows, which each emit coolant in the downstream direction on their respective sides of the airfoil. This region is thus relatively starved of coolant flow and adequate cooling is achieved inefficiently with a high density of holes expelling a large amount of coolant in order to dilute the nearby mainstream flow. Drawing inspiration from recent literature on reverse-blowing film cooling holes, several film cooling geometries have been designed and tested with a view to improving upon this situation by blowing coolant from each side of the airfoil geometric stagnation line to the other in a criss-cross pattern. This is found to be capable of producing much higher film effectiveness near the stagnation line than a series of more conventional designs which were also tested, without decreasing downstream film effectiveness. A method is also described for using experimental film effectiveness data to estimate two novel measures of the efficiency of leading edge film coolant usage: the proportion of the mainstream which interacts with leading edge film coolant and the proportion of coolant from the two most upstream film hole rows which reaches the stagnation line.

Charged Exciton Dissociation Energy in (Cd,Mn)Te Quantum Wells with Variable Disorder and Carrier Density

We report on the magneto-photoluminescence of (Cd,Mn)Te/(Cd,Mg)Te quantum wells excited by photons with varied energy. We observe that laser illumination modifies the carrier density and Coulomb disorder in the quantum wells. Three different regimes are analyzed, corresponding to low hole density with low disorder, low hole density with significant disorder, and high hole density. By using the diluted magnetic semiconductor as a quantum well material, we can induce the spin singlet–triplet transition of charged excitons in a magnetic field. This transition is then used as a tool to determine the charged exciton dissociation energy. With this approach, we find the same value for the dissociation energy in all the regimes of hole density and disorder. Our result is compared with the dissociation energy obtained from the PL splitting between the X and X^{!! +} lines at zero field, which exhibits significantly greater variation.

High-electron-affinity oxide V2O5 enhances surface transfer doping on hydrogen-terminated diamond

Diamond exhibits many desirable properties that could benefit the development of future carbon-based electronic devices. Its hydrogen-terminated surface, in conjunction with a suitable surface acceptor, develops a two-dimensional (2D) p-type surface conductivity through the surface transfer doping mechanism which can then be harvested for constructing functional devices. In this study, we have revisited the surface transfer doping of diamond by a high electron affinity (EA) transition metal oxide, V2O5. Through a combination of in-situ electrical measurements, Hall effect measurements and first-principles density functional theory (DFT) calculations, we explicitly show the intrinsic surface transfer doping behavior of V2O5, with doping performance superior to other competing TMOs such as MoO3. The metallic surface conduction of diamond induced by V2O5 is persistent down to 250 mK; this when coupled with the high hole density exceeding 7 × 1013 cm−2 offers a promising platform for the development of advanced diamond surface electronics exploiting many interesting quantum transport properties of the 2D hole layer of diamond.

Effect of deformation due to stretching of the Gas Electron Multiplier (GEM) Foil

The Gas Electron Multiplier (GEM) was first introduced by Fabio Sauli in 1997, which is a thin layer of an insulating polymer, coated on both sides with copper and chemically perforated with a high density of microscopic holes. The GEM detectors, which are built using GEM foils, have been utilized for various applications due to their excellent spatial resolution, high rate capabilities and flexibility in design. Large area of triple GEM detectors are planned in experiments as it is the case in the upgrade of the CMS forward muon system. During the assembly of these detectors, the GEM foils are manually stretched to maintain the required gap configuration throughout the detector area. This stretching procedure can introduce local variation in the size or the shape of the perforated holes in GEM foil which can further vary the operational characteristics of the foil as well as the detector. Therefore, the distribution and size of the holes over a GEM foil should be uniform to achieve homogeneous functionality of the detector over the active surface. We can prevent the deformation of the perforated holes by optimizing the stretching force which is used during the assembly.

The Impact of Channel Semiconductor on the Memory Characteristics of Ferroelectric Field-Effect Transistors

In this work, channel semiconductor is identified and demonstrated to have significant impact on the memory characteristics of ferroelectric field-effect transistors (Fe-FETs). It is understood that, to achieve high electron density at on-state, it requires high hole density at the off-state to realize the charge balance and strong ferroelectric polarization switching in n-type Fe-FETs. Therefore, Fe-FETs with a wider bandgap semiconductor channel have a much smaller memory window than Fe-FETs with a narrower bandgap semiconductor channel due to the insufficient polarization switching. The simple device physics suggests that narrow bandgap semiconductor channel such as Ge is preferred for Fe-FETs with large memory window.

Salt‐Assisted Growth of P‐type Cu9S5 Nanoflakes for P‐N Heterojunction Photodetectors with High Responsivity

AbstractP‐n junctions based on two dimensional (2D) van der Waals (vdW) heterostructure are one of the most promising alternatives in next‐generation electronics and optoelectronics. By choosing different 2D transition metal dichalcogenides (TMDCs), the p‐n junctions have tailored energy band alignments and exhibit superior performance as photodetectors. The p‐n diodes working at reverse bias commonly have high detectivity due to suppressed dark current but suffer from low responsivity resulting from small quantum efficiency. Greater build‐in electric field in the depletion layer can improve the quantum efficiency by reducing recombination of charge carriers. Herein, Cu9S5, a novel p‐type semiconductor with direct bandgap and high optical absorption coefficient, is synthesized by salt‐assisted chemical vapor deposition (CVD) method. The high density of holes in Cu9S5 endows the constructed p‐n junction, Cu9S5/MoS2, with strong build‐in electric field according to Anderson heterojunction model. Consequently, the Cu9S5/MoS2 p‐n heterojunction has low dark current at reverse bias and high photoresponse under illumination due to the efficient charge separation. The Cu9S5/MoS2 photodetector exhibits good photodetectivity of 1.6 × 1012 Jones and photoresponsivity of 76 A W−1 under illumination. This study demonstrates Cu9S5 as a promising p‐type semiconductor for high‐performance p‐n heterojunction diodes.

Investigation of nitrogen polar p-type doped GaN/AlxGa(1-x)N superlattices for applications in wide-bandgap p-type field effect transistors

In this study, the metal-organic chemical vapor deposition growth and electrical properties of N-polar modulation doped p-AlGaN/GaN superlattices (SLs) were investigated. Hole sheet charge density and mobility were studied as a function of the concentration of the p-type dopant Mg in the SL and the number of SL periods. Room temperature Hall measurements were carried out to determine the hole mobility and the sheet charge density. While the hole density increased with the increasing number of SL periods, the hole mobility was largely unaffected. Hole mobilities as high as 18 cm2/V s at a simultaneously high hole density of 6.5 × 1013 cm−2 were observed for N-polar SLs with a Mg modulation doping of 7.5 × 1018 cm−3. For comparable uniformly doped Ga-polar SL samples, a mobility of 11 cm2/V s was measured. These results confirm the presence of abrupt Mg doping profiles in N-polar p-type GaN/AlxGa(1−x)N SL, allowing the demonstration of SLs with properties comparable to those of state-of-the-art Ga-polar modulation doped AlGaN/GaN SLs grown using molecular beam epitaxy. The lowest sheet resistance in the GaN/AlGaN material system of 5 kΩ/◻ is also reported. Test-structure transistors were also fabricated to investigate the applicability of these SL structures, with the planar device resulting in a current of 5 mA/mm and a FinFET structure resulting in a current of over 100 mA/mm.

Modifying the structure, emulsifying and rheological properties of water-soluble protein from chicken liver by low-frequency ultrasound treatment

The influence of low-frequency ultrasound on the structure, emulsifying and rheological properties of water-soluble protein from chicken liver (CLWP) was investigated. CLWP solutions (10%, w/v) were treated by ultrasound for 4 min at a frequency of 20 kHz (UCLWP, amplitude 50% at an output 100 W, 11.5 W/cm2). The secondary and tertiary structure and thermal denaturation properties were changed in UCLWP. However, SDS-PAGE showed no changes in the subunit compositions between UCLWP and CLWP. Surface hydrophobicity and sulfhydryl groups of UCLWP increased demonstrating partial unfolding of water-soluble proteins and reduced its intermolecular interactions by ultrasound effect. UCLWP showed the smaller and more uniform particles with high-density holes. Furthermore, emulsifying activity index and emulsion stability index of UCLWP had a significant improvement over that of CLWP. UCLWP had lower shear stress and motion resistance during the rheological evaluation. These modifications of the structure, emulsifying and rheological properties for UCLWP could expand the application of chicken liver protein and increase the added value of chicken liver by-products.

Disappeared deep charge-states transition levels in the p-type intrinsic CsSnCl3 perovskite

Lead-free inorganic perovskites are promising for optoelectronic applications. Understanding their phase diagram and defect properties is beneficial to predict the stable phase and applications. Here, taking CsSnCl3 as an example, the stability and defect properties are investigated systemically. The results show that the stoichiometric CsSnCl3 can only be grown in a narrow area determined by Sn and Cs chemical potentials. No matter what the Sn condition is, both acceptor defects (Cs- and Sn-vacancies with low charge states) are formed spontaneously with negative formation energies, and the donor defects are difficult to be formed with high formation energies. Interestingly, these charge-state transition levels induced by such stable defects are in the valence band. Meanwhile, no deep acceptor and donor states are formed in the bandgap. In addition, although the Fermi levels can vary in a wide range, the Fermi levels are pinned in the valence band, irrespective of the atmospheric conditions, leading to p-type CsSnCl3 with high hole density and low electron density. Such electronic characters are elucidated in detail by the atomic orbitals and structural deformations. Our studies provide an insight view of the defect properties of CsSnCl3 and provide a valuable guideline for CsSnCl3 fabrication and further modulation.

Effect of substituted nitrogen atom location on the photophysical and charge transporting properties of carboline derivatives

In this work, three carboline derivatives, 9,9′-m-phenylenedi-α-carboline (NmCP1), 9,9′-m-phenylenedi-β-carboline (NmCP2), and 9,9′-m-phenylenedi-γ-carboline (NmCP3) were designed and synthesized to examine the effect of nitrogen atom position on the photophysical and charge transport properties of carboline derivatives. NmCP1 with α-carboline showed high hole and electron current density in the single carrier device owing to formation of π-π stacking by weak hydrogen bond between α-carbaoline and a phenyl linker from single crystal analysis. Whereas, NmCP2 and NmCP3 were advantageous to increase the triplet energy due to the distortion of the carboline unit from the central phenyl unit. Among the three compounds, the NmCP1 achieved high external quantum efficiency of 18.6% in the deep blue phosphorescent organic light-emitting diodes. Therefore, the control of the nitrogen position could manage the carrier transport properties, photophysical properties and device performances of the carboline derivatives. • Design and synthesis of three carboline derivatives with different nitrogen positions. • Efficient charge transport properties by molecular stacking in the carboline derivatives. • High external quantum efficiency close to 20% in the deep blue phosphorescent organic light-emitting diodes.

The effect of hole density variation in the PECVD reactor showerhead on the deposition of amorphous carbon layer

In the showerhead structure composed of two stages of porous media, the changes in the ACL (Amorphous Carbon Layer) deposition rate and extinction coefficient were experimentally analyzed and numerically simulated. Depositions were carried out by applying perforated plates with various hole densities in the central region under the conditions of C3H6/N2/He plasma and a 550 °C heater temperature. With a uniform hole density as a reference case, the deposition rate decreased with increasing process pressure, and the maximum deposition rate of 2707 Å/min was achieved at 733 Pa. The deposition rate decreased with the reduced residence time at the total flow rate of over 2000 sccm. The extinction coefficient decreased drastically with increasing molar concentration of C3H6 and process pressure. In the case of a high hole density pattern, the deposition rate of the central region of the wafer decreased, but the change of the extinction coefficient was insignificant, while the velocity of the fluid at the center portion was accelerated and the residence time varied with the gradient of velocity. The ACL growth could be optimized by controlling the velocity gradient of the fluid, which could be achieved by modifying the hole density of the perforated plate.

Maximizing the utility of single atom electrocatalysts on a 3D graphene nanomesh

Vertically aligned N-doped graphene nanomesh arrays (VNGNMAs) with a high density of in-plane surface holes and out-of-plane interconnected, vertically aligned structures as a scaffold can facilitate the diffusion of reactants and maximize the utility of single atoms in the liquid phase.

High-aspect ratio mechanical microdrilling process for a microhole array of nitride ceramics

In semiconductor industry, wafer testing requires a microhole array constructed by high-density holes below ϕ 100 μm for stabilizing the microprobe used in conduction testing. This study conducted mechanical microdrilling experiments of a nitride ceramic sheet to investigate the effects of drilling parameters on quality characteristics of the microhole drilled. Fabrications of a high-aspect ratio microhole must be implemented by segmented machining. A center pilot hole was first made and then drilled the microhole by a two-segment process. Drilling factors analyzed in this study included depth of the center pilot hole, depth ratio of the hole segments, and machining parameters of cutting speed (spindle rotation rate), tool feed rate, and step in peck drilling in the microdrilling. Because both diameter and position of the microhole affect the functionality of hole array directly, this is a multi-objective problem. This study proposes a new decision method for deriving the optimal parameter level set in the multi-object problem based on the level effects obtained from Taguchi’s analyses. In addition, this study used a scanning electron microscopy (SEM) to observe the influences of drilling stroke on flank wear of the microdrill. This study implemented two series experiments of ϕ 69 μm and ϕ 55 μm with aspect ratios of 15.36 and 11.64, respectively. Experimental results indicate that applying the optimal parameter level set derived in ϕ 55 μm experiment could obtain excellent performances after the drilling stroke of 384 mm, 600 holes drilled. The microdrills have fulfilled a high use efficiency.

Alternative simple method to realize p-type BaSi2 thin films for Si heterojunction solar cell applications

Abstract:A novel preparation method of B-doped p-type BaSi2 (p-BaSi2) is proposed to realize heterojunction crystalline Si solar cells with p-BaSi2. The method consists of thermal evaporation of BaSi2 on B-doped amorphous Si (a-Si). In this study, the effect of a-Si interlayers and substrate temperature during BaSi2 evaporation on the electrical characteristics and crystalline quality of the evaporated films were investigated. While no cracks were found in the BaSi2 films formed using hydrogenated a-Si deposited by plasma enhanced chemical vapor deposition (PECVD), the films formed with sputtered a-Si have cracks. In addition, BaSi2 films formed with a 600 °C substrate temperature using PECVD a-Si showed p-type characteristics. After a post-deposition anneal at 800 °C for 5 minutes, the film hole density was measured at 1.3×1019 cm-3 and boron was found to be uniformly distributed throughout the film. These results show that the proposed method using PECVD is promising to obtain p-BaSi2 thin films with high hole density for p-BaSi2/n-type crystalline Si heterojunction solar cells.

Simulation Study of a Novel Snapback-Free and Low Turn-Off Loss Reverse-Conducting IGBT With Controllable Trench Gate

A novel ultra-fast snapback-free controllable trench gate (CTG) reverse-conducting insulated gate bipolar transistor (RC-IGBT) is proposed and investigated by simulation. It features a CTG in the collector side and a bias voltage ( ${V}_{\text {RC}}$ ) is applied between the CTG and collector electrode. In the forward conduction state with ${V}_{{\text {RC}}} , a high-density hole inversion layer is formed around the CTG. The CTG acts as not only a folded controllable hole injector to enhance the hole injection efficiency, but also an electron barrier to increase the distributed resistance. The CTG RC-IGBT achieves a low on-state voltage drop ( ${V}_{{ \mathrm{\scriptscriptstyle ON}}}$ ) and snapback-free with a small cell pitch. In the blocking state with ${V}_{\text {RC}} > {0}$ , an electron accumulation layer is formed around the CTG. The electron layer together with the CTG acts as an equivalent N-buffer layer to stop the electric field and support high breakdown voltage. During turn-off, the CTG RC-IGBT behaves like a unipolar device without long tail current because the hole injection is deactivated by properly switching the ${V}_{\text {RC}}$ . Compared with conventional RC-IGBT, the proposed device decreases the ${V}_{\text {on}}$ and turn-off energy loss ( ${E}_{\text{off}}$ ) by 34% and 74%, respectively, under the load current of 100 A/cm2 and bus voltage of 600 V.

Metal Templates and Boron Sources Controlling Borophene Structures: An Ab Initio Study

Interlayer binding of 2D borophene phases are determined as a function of hole density (HD) and metal surfaces Cu, Ag, and Au. The Cu surface prefers formation of monolayers whereas the Au surface shows multilayer stacking. Ag surface enables formation of monolayers with higher HD and bilayers for borophenes with lower HD. The growth pattern of bilayers on metal templates are investigated using ab-initio molecular dynamic simulations. Formation of icosahedral B12 clusters and extension to sheets are also studied on Cu surface. Icosahedral sheet formation by boron atom deposition is found to be a thermodynamically unfavorable process on this surface. Thus, structure of borophene phases could also be tuned by modulating the parameters such as boron source or the metal templates, in addition to the substrate temperature and boron atom deposition rate.

Asperomagnetic order in diluted magnetic semiconductor (Ba,Na)(Zn,Mn)2As2

We report an investigation of magnetic ordering in (Ba,Na)(Zn,Mn)2As2 (BNZMA) single crystals, a type of II-II-V magnetic semiconductor based on BaZn2As2, with a combination of magnetic, electron transport, and spin polarization measurements. At temperatures above 90 K, the susceptibility is found to follow the Curie-Weiss law with a Curie-Weiss temperature of 16 K. At low temperatures, both the dc and ac susceptibilities exhibit spin-glass-like features and the electron spin polarization is determined to be 48 ± 8% using Andreev reflection spectroscopy. Our experimental results suggest that the ground state of BNZMA has an asperomagnetic order, an intermediate regime between a ferromagnet and a canonical spin glass. Such a partially spin polarized glassy phase can be attributed to the competition between the short range antiferromagnetic superexchange interaction and the long range ferromagnetic/antiferromagnetic exchange interactions mediated by high-density holes.

Two-Dimensional Holey Nanoarchitectures Created by Confined Self-Assembly of Nanoparticles via Block Copolymers: From Synthesis to Energy Storage Property.

Advances in liquid-phase exfoliation and surfactant-directed anisotropic growth of two-dimensional (2D) nanosheets have enabled their rapid development. However, it remains challenging to develop assembly strategies that lead to the construction of 2D nanomaterials with well-defined geometry and functional nanoarchitectures that are tailored to specific applications. Here we report a facile self-assembly method leading to the controlled synthesis of 2D transition metal oxide (TMO) nanosheets containing a high density of holes. We utilize graphene oxide sheets as a sacrificial template and Pluronic copolymers as surfactants. By using ZnFe2O4 (ZFO) nanoparticles as a model material, we demonstrate that by tuning the molecular weight of the Pluronic copolymers we can incorporate the ZFO particles and tune the size of the holes in the sheets. The resulting 2D ZFO nanosheets offer synergistic characteristics including increased electrochemically active surface areas, shortened ion diffusion paths, and strong inherent mechanical properties, leading to enhanced lithium-ion storage properties. Postcycling characterization confirms that the samples maintain structural integrity after electrochemical cycling. Our findings demonstrate that this template-assisted self-assembly method is a useful bottom-up route for controlled synthesis of 2D nanoarchitectures, and these holey 2D nanoarchitectures are promising for improving the electrochemical performance of next-generation lithium-ion batteries.

Low temperature fabrication of CuxO thin-film transistors and investigation on the origin of low field effect mobility

Cuprous (Cu2O) and cupric (CuO) oxide thin films have been deposited by radio frequency magnetron sputtering with two different oxygen partial pressures. The as-deposited copper oxide films were subjected to post-annealing at 300 °C for 30 min to improve the microstructural, morphological, and optical properties of thin films. Optical absorption studies revealed the existence of a large number of subgap states inside CuO films than Cu2O films. Cu2O and CuO thin film transistors (TFTs) were fabricated in an inverted staggered structure by using a post-annealed channel layer. The field effect mobility values of Cu2O and CuO TFTs were 5.20 × 10−4 cm2 V−1 s−1 and 2.33 × 10−4 cm2 V−1 s−1, respectively. The poor values of subthreshold swing, threshold voltage, and field effect mobility of the TFTs were due to the charge trap density at the copper oxide/dielectric interface as well as defect induced trap states originated from the oxygen vacancies inside the bulk copper oxide. In order to study the distribution of the trap states in the Cu2O and CuO active layer, the temperature dependent transfer characteristics of transistors in the temperature range between 310 K and 340 K were studied. The observed subgap states were found to be decreasing exponentially inside the bandgap, with CuO TFT showing higher subgap states than Cu2O TFT. The high-density hole trap states in the CuO channel are one of the plausible reasons for the lower mobility in CuO TFT than in Cu2O TFT. The origin of these subgap states was attributed to the impurities or oxygen vacancies present in the CuO channel layer.