Rms Surface Roughness Research Articles

Enhancing two-dimensional growth of high-temperature AlN buffer to improve the quality of GaN on Si grown by ex situ two-step method

GaN epitaxial films were grown on Si substrates by ex situ two-step method combining the technologies of pulsed laser deposition (PLD) and metal organic chemical vapor deposition (MOCVD). The N/Al ratio of high-temperature AlN (HT-AlN) buffer layer was optimized, and its influence on the HT-AlN growth mode as well as the quality of GaN epitaxial films was investigated. When the N/Al ratio was 500, the two-dimensional growth of HT-AlN was greatly enhanced, and it obtained a coalesced and smooth surface with the minimum RMS surface roughness as 1.63 nm. The as-grown GaN epitaxial film had the best crystalline quality with the minimum full-width at half maximums of GaN(0002) and GaN(10 1¯ 2) as 0.14° and 0.22°, respectively. Owing to the high energy of PLD, the ex situ low-temperature AlN template had an abrupt Si/AlN interface and flat surface, which was of significance to improve the quality of HT-AlN buffer and GaN film.

Selective control of surface characteristics of magnesite and quartz by a novel silicophilic collector stearylamine acetate

Reverse flotation desiliconization from magnesite is significant for the exploitation of complex and barren magnesite resources. In this process, a critical issue is to find efficient and selective chemicals as flotation collectors. Herein, a cationic surfactant stearylamine acetate (SAA) was first used as a collector for the separation of magnesite and quartz. Micro-flotation experiments demonstrate that quartz can be separated from magnesite with a high Gaudin’s selectivity index of 6.51 at slurry pH 5.0 and 70 mg/L SAA. Measurements of zeta potential and contact angle show that SAA selectively increased the surface charge and hydrophobicity of quartz. Field emission scanning electron microscopy (FESEM/EDS) and atomic force microscope (AFM) imaging indicate greater adsorption density of SAA on quartz than magnesite, with significantly higher nitrogen element content and RMS surface roughness of quartz. We also used surface-sensitive time of flight secondary ion mass spectrometry (TOF-SIMS) and FTIR spectroscopy to characterize the selective adsorption of SAA on quartz from quartz-magnesite mixtures. Apart from electrostatic attraction, it is found that the selective adsorption was attributed to hydrogen bonding formed between the −N–H group of SAA and the oxygen atom of the O-Si-O group on quartz surface.

Materials removal mechanism for ultra-precise cutting of single-crystal silicon with natural single-crystal diamond tools by experiment and atomic simulation

The influence of tool rake angle and cutting speed on the ultra-precision cutting of single crystal silicon with natural single crystal diamond tools is studied by experiment and molecular dynamics (MD) simulations. The findings demonstrate that the 0° rake angle tool attains superior surface quality, reduced cutting force and friction coefficient in comparison to the −10° and − 20° rake angle tools. Moreover, the MD results reveal that a smaller negative rake angle tool can decrease the formation of high pressure phase atoms and other defects. In addition, the PV, RMS and Ra surface roughness parameters decrease as the machine spindle speed increases. Additionally, higher cutting speeds improve the surface morphology of the machined workpiece and produce fewer defective atoms.

Realization of CO2 gas sensors and broadband photodetectors using metal/high-k CeO2/p-Si heterojunction

Realization of high-k dielectric oxide material-based devices such as photodetectors (PDs)/gas sensors fabricated on silicon substrate seems to be the utmost promising as a cost-effective approach to use in next generation optoelectronic field. We have explored metal/CeO2/p-Si heterojunction to construct as a broadband (BB) PD and CO2 gas sensor device. The effect of post-annealing procedure on photodetection and CO2 gas sensing characteristics were correlated using AFM, XRD, XPS, Raman and UV–Vis studies. At 0 V bias, the fabricated as-deposited Au/CeO2/p-Si PD device exhibits outstanding performance with enhanced responsivity of 85 AW−1 (at 910 nm), detectivity of 1.36×1015 Jones (at 850 nm), EQE of 1.3×104 % (at 850 nm), faster rise and fall times of 124 ms and 107 ms (at 900 nm). On the other hand, the photodetection characteristic parameters were slightly deteriorated as a function of annealing with respect to the as-deposited device. One of the causes for this fact was attributed to the increase in rms surface roughness (AFM) and decrease in absorbance of CeO2 thin film (UV–Vis). Additionally, Ag/CeO2/p-Si heterojunction was studied as a CO2 gas sensor and evaluated response/recovery times as a function of CO2 gas concentration. Sensing responses of CeO2 as-deposited, CeO2-400, CeO2-500, CeO2-600 and CeO2-700 °C were around 58, 60, 62, 81 and 90 %, respectively, when exposed to 200 ppm of CO2. Thus, we validate that the prospect of integrating enhanced performance in BB PDs and CO2 gas sensors using metal/CeO2/p-Si heterojunction could serve as a basic building block in near future optoelectronic applications. Furthermore, the effect of post-annealing temperature on the morphological, structural, BB photodetection and CO2 gas sensing properties were discussed in detail.

Analytical study of KOH wet etch surface passivation for III-nitride micropillars

III-Nitride micropillar structures show great promise for applications in micro light-emitting diodes and vertical power transistors due to their excellent scalability and outstanding electrical properties. Typically, III-Nitride micropillars are fabricated through a top-down approach using reactive ion etch which leads to roughened, nonvertical sidewalls that results in significant performance degradation. Thus, it isessential to remove this plasma etch induced surface damage. Here, we show that potassium hydroxide(KOH) acts as a crystallographic etchant for III-Nitride micropillars, preferentially exposing the vertical m-plane, and effectively removing dry etch damage and reducing the structure diameter at up to 36.6nm/min. Both KOH solution temperature and concentration have a dramatic effect on this wet etch progression. We found that a solution of 20% AZ400K (2% KOH) at 90°C is effective at producingsmooth, highly vertical sidewalls with RMS surface roughness as low as 2.59nm, ideal for high-performance electronic and optoelectronic devices.

Influence of swift heavy ion irradiation on charge transport and conduction mechanisms across the interface of LaMnO3 and La0.7Ca0.3MnO3 manganites

Swift heavy ion (SHI) irradiated LaMnO3/La0.7Ca0.3MnO3 (LMO/LCMO) interfaces have been investigated to understand their charge transport and conduction mechanisms. Prominent effect of ion fluence has been discussed for the interface resistivity behaviors and metal to insulator phase transition for LMO/LCMO interfaces on the bases of lattice strain, crystalline granular state, crystalline imperfection, average grain size, grain boundary density and rms surface roughness. Field effect configuration (FEC) has been employed to study the interesting modifications in the irradiated LMO/LCMO interface resistivity under different applied electric fields to understand the depletion region, free charge carrier density, ferromagnetic phase fractions and crystal field based distortions. A Phenomenological percolation model has been employed to understand the role of phase separation in governing the charge conduction processes across LMO/LCMO interfaces.

Dendrite Growth—Microstructure—Stress—Interrelations in Garnet Solid‐State Electrolyte

AbstractThis study illustrates how the microstructure of garnet solid‐state electrolytes (SSE) affects the stress‐state and dendrite growth. Tantalum‐doped lithium lanthanum zirconium oxide (LLZTO, Li6.4La3Zr1.4Ta0.6O12) is synthesized by powder processing and sintering (AS), or with the incorporation of intermediate‐stage high‐energy milling (M). The M compact displays higher density (91.5% vs 82.5% of theoretical), and per quantitative stereology, lower average grain size (5.4 ± 2.6 vs 21.3 ± 11.1 µm) and lower AFM‐derived RMS surface roughness contacting the Li metal (45 vs 161 nm). These differences enable symmetric M cells to electrochemically cycle at constant capacity (0.1 mAh cm−2) with enhanced critical current density (CCD) of 1.4 versus 0.3 mA cm−2. It is demonstrated that LLZTO grain size distribution and internal porosity critically affect electrical short‐circuit failure, indicating the importance of electronic properties. Lithium dendrites propagate intergranularly through regions where LLZTO grains are smaller than the bulk average (7.4 ± 3.8 µm for AS in a symmetric cell, 3.1 ± 1.4 µm for M in a half‐cell). Metal also accumulates in the otherwise empty pores of the sintered compact present along the dendrite path. Mechanistic modeling indicates that reaction and stress heterogeneities are interrelated, leading to current focusing and preferential plating at grain boundaries.

(Invited) Gallium Nitride for Vertical Power Devices: Improving Morphology and Unintentional Impurities for Better Devices

While GaN has been researched for many years as a material for light emitting diodes, lasers, high electron mobility transistors, and other devices, further improvements to material purity are still needed to realize the full potential of this material for vertical device applications. To achieve high quality, high purity GaN for power devices, our research employs ammonia-assisted molecular beam epitaxy (NH3-MBE) and plasma-assisted molecular beam epitaxy (PA-MBE). Past studies of fast growth rates (more than 1 μm/hr) and ultra-low impurity incorporation revealed that both PAMBE and NH3-MBE can achieve low net doping levels, and NH3-MBE as low as 1x1015 cm-3.1 However, This work also indicated that impurity incorporation increased with increasing growth rate.Recent research efforts have focused on further improvements to morphology and unintentional dopants in NH3-MBE-grown homoepitaxial layers with fast growth rates. By optimizing growth conditions for faster growth rates and using indium as a surfactant, devices with drift layers up to 10 μm thick were grown. These layers exhibited smooth surface morphology as seen in AFM scans with RMS surface roughness as low as 0.21 nm for a 2x2 μm2 scan area.2 Adding the In surfactant also led to reduced incorporation of unintentional Si impurities in UID films as shown by SIMS depth profiles for GaN films grown with and without In. The extremely low impurity levels were further confirmed by CV measurements which indicated that the net doping density in the UID GaN layers decreased from 2x1016 cm-3 to 5x1015 cm-3 with the addition of the In surfactant.2 Based on these UID levels and the theoretical critical electric field of GaN (3 MV/cm), drift layers up to 29.5 μm and 7.4 μm can be depleted with a triangular electric field profile for net donor concentrations of 5x1015 cm-3 and 2x1016 cm-3, respectively. Devices with the same net concentrations with drift regions 3 μm thick can hold voltages of 854 V and 717 V, respectively.Based on the previously described studies of low-impurity GaN at different growth rates, we developed vertical p-n GaN power devices grown by NH3 MBE.3 These p-n diodes contained a 0.25 µm n+ region, 4 µm n- region with 3x1015 cm-3 unintentional carriers, 0.4 µm p+ region and 10nm p++ capping layer to improve the ohmic anode contact. The circular diodes were fabricated with Pd/Pt anode contacts and Ti/Au cathode contacts. Device diameters were between 80 and 100 µm. The devices featured a 15 µm field plate made from Ti/Au contacts on top of an Al2O3/Si3N4 dielectric stack.The diodes exhibited outstanding forward J-V behavior with a low specific on-resistance (Ron,sp) of 0.28 mΩ-cm2 and a minimum ideality factor of 1.36, which are among the best achieved among similar homoepitaxial GaN p-n diodes.3-5 The best diodes also exhibited a breakdown voltage of > 1 kV (equipment limit 1 kV). The reverse-voltage properties indicate that punch-through was achieved with a peak electric field (EC) >2.6 MV/cm, as confirmed by Silvaco simulations (Fig. 7). The combination of >1 kV breakdown voltage and on-resistance of 0.28 mΩ-cm2 represents one of the best performances of the p-n GaN diodes, achieved with a significantly thinner drift layer compared to comparable MOCVD GaN p-n diodes with drift layers more than 8 µm. Work is ongoing to develop NH3-MBE p-n diodes with indium surfactant-assisted drift layer growth which shows promise to further improve the surface morphology, reduce leakage, and enhance breakdown performance of the vertical devices.

Quantum Cascade Lasers Grown by Metalorganic Chemical Vapor Deposition on Foreign Substrates with Large Surface Roughness

The surface morphology of a buffer template is an important factor in the heteroepitaxial integration of optoelectronic devices with a significant lattice mismatch. In this work, InP-based long-wave infrared (~8 µm) emitting quantum cascade lasers with active region designs lattice-matched to InP were grown on GaAs and Si substrates employing InAlGaAs step-graded metamorphic buffer layers, as a means to assess the impact of surface roughness on device performance. A room-temperature pulsed-operation lasing with a relatively good device performance was obtained on a Si template, even with a large RMS roughness of 17.1 nm over 100 µm2. Such results demonstrate that intersubband-operating devices are highly tolerant to large RMS surface roughness, even in the presence of a high residual dislocation density.

Sub-10 μm-Thick Ge Thin Film Fabrication from Bulk-Ge Substrates via a Wet Etching Method.

Low-defect density Ge thin films are crucial for studying the impact of defect density on the performance limits of Ge-based optical devices (optical detectors, LEDs, and lasers). Ge thinning is also important for Ge-based multijunction solar cells. In this work, Ge wet etching using three acidic H2O2 solutions (HF, HCl, and H2SO4) was studied in terms of etching rate, surface morphology, and surface roughness. HCl-H2O2-H2O (1:1:5) was demonstrated to wet-etch 535 μm-thick bulk-Ge substrates to 4.1 μm with a corresponding RMS surface roughness of 10 nm, which was the thinnest Ge film from bulk-Ge via a wet etching method to the best of our knowledge. The good quality of pre-etched bulk-Ge was preserved, and the low threading dislocation density of 6000-7000 cm-2 was maintained after the etching process. This approach provides an inexpensive and convenient way for accurate Ge substrate thinning in applications such as multijunction solar cells and sub-10 μm-thick Ge thin film preparation, which enables future studies of low-defect density Ge-based devices such as photodetectors, LEDs, and lasers.

Chemical vapor deposition growth of [formula omitted] on Si- and C- face off-axis 4H–SiC at high temperature

Realization of β‐Ga2O3 on a high-thermal-conductivity substrate is crucial to overcome the poor thermal conductivity of β‐Ga2O3 which is one of the major roadblocks against its era in power electronics. We investigated low-pressure chemical vapor deposition (LPCVD) growth on both Si and C- face (0001) 4H–SiC at a high growth temperature of 925 °C using Ga metal and O2 gas source. Growths on C-face 4H–SiC resulted polycrystalline β‐Ga2O3 for the entire O2-flow range, whereas under optimized O2-flow conditions, step flow growth of (−201) β‐Ga2O3 was achieved on Si-face 4H–SiC with 3.7 nm rms surface roughness and rocking curve FWHM of 0.54° at a growth rate reaching 2.48 μm/h 4° off-axis nature of the substrate promoted the growth of some of the in-plane rotational domains while suppressing others. Raman measurements further verified the pure β‐Ga2O3 nature of the grown films. Using a customized LPCVD with solid source Ga, a cost-effective, safe and industrially scalable method was shown to pave the way to enable β‐Ga2O3 heteroepitaxy on 4H–SiC for high-power electronics.

Ultra-low resistance Au-free V/Al/Ti/TiN ohmic contacts for AlGaN/GaN HEMTs

We report on the electrical and microstructural characterization of an Au-free V/Al/Ti/TiN ohmic contact for AlGaN/GaN heterostructures. Ultra-low contact resistance and specific contact resistivity of Rc < 0.1 Ω mm and ρc < 2.4 × 10−7 Ω cm2 have been achieved with very low RMS surface roughness. This was accomplished at a comparably low annealing temperature of 800 °C and without applying any contact recess, regrowth, or implantation process. High electron mobility transistors were fabricated and a comparison of the electrical performance with state-of-the-art Ti/Al/Ti/TiN and Ti/Al/Ni/Au contacts was made. The contact formation mechanism is discussed on the basis of microstructural features.

Adsorption behavior of serum proteins on anodized titanium is driven by surface nanomorphology.

Protein adsorption behavior can play a critical role in defining the outcome of a material by affecting the subsequent in vivo response to it. To date, the effect of surface properties on protein adsorption behavior has been mainly focused on surface chemistry, but research on the effect of nanoscale surface topography remains limited. In this study, the adsorption behavior of human serum albumin, immunoglobulin G, and fibrinogen in terms of the adsorbed amount and conformational changes were investigated on bare and anodized titanium (Ti) samples (40 and 60 V applied voltages). While the surface chemistry, RMS surface roughness, and arithmetic surface roughness of the anodized samples were similar, they had distinctly different nanomorphologies identified by atomic force microscopy and scanning electron microscopy, and the surface statistical parameters, surface skewness Ssk and kurtosis Sku. The Feret pore size distribution was more uniform on the 60 V sample, and surface nanostructures were more symmetrical with higher peaks and deeper pores. On the other hand, the 40 V sample surface presented a nonuniform pore size distribution and asymmetrical surface nanostructures with lower peaks and shallower pores. The amount of surface-adsorbed protein increased on the sample surfaces in the order of Ti < 40 V < 60 V with the predominant factor affecting the amount of surface-adsorbed protein being the increased surface area attained by pore formation. The secondary structure of all adsorbed proteins deviated from that of their native counterparts. While comparing the secondary structure components of proteins on anodized surfaces, it was observed that all three proteins retained more of their secondary structure composition on the surface with more uniform and symmetrical nanofeatures than the surface having asymmetrical nanostructures. Our results suggest that the nanomorphology of the peaks and outer walls of the nanotubes can significantly influence the conformation of adsorbed serum proteins, even for surfaces having similar roughness values.

Tunable bandgap and Si-doping in N-polar AlGaN on C-face 4H-SiC via molecular beam epitaxy

N-polar AlGaN is an emerging wide-bandgap semiconductor for next-generation high electron mobility transistors and ultraviolet light emitting diodes and lasers. Here, we demonstrate the growth and characterization of high-quality N-polar AlGaN films on C-face 4H-silicon carbide (SiC) substrates by molecular beam epitaxy. On optimization of the growth conditions, N-polar AlGaN films exhibit a crack free, atomically smooth surface (rms roughness ∼ 0.9 nm), and high crystal quality with low density of defects and dislocations. The N-polar crystallographic orientation of the epitaxially grown AlGaN film is unambiguously confirmed by wet chemical etching. We demonstrate precise compositional tunability of the N-polar AlGaN films over a wide range of Al content and a high internal quantum efficiency ∼74% for the 65% Al content AlGaN film at room temperature. Furthermore, controllable silicon (Si) doping in high Al content (65%) N-polar AlGaN films has been demonstrated with the highest mobility value ∼65 cm2/V-s observed corresponding to an electron concentration of 1.1 × 1017 cm−3, whereas a relatively high mobility value of 18 cm2/V-s is sustained for an electron concentration of 3.2 × 1019 cm−3, with an exceptionally low resistivity value of 0.009 Ω·cm. The polarity-controlled epitaxy of AlGaN on SiC presents a viable approach for achieving high-quality N-polar III-nitride semiconductors that can be harnessed for a wide range of emerging electronic and optoelectronic device applications.

Hard and Highly Adhesive AlMgB14 Coatings RF Sputtered on Tungsten Carbide and High-Speed Steel

We report a new industrial application of aluminum magnesium boride AlMgB14 (BAM) coatings to enhance the hardness of tungsten carbide ceramic (WC-Co) and high-speed steel tools. BAM films were deposited by RF magnetron sputtering of a single dense stoichiometric ceramic target onto commercial WC-Co turning inserts and R6M5 steel drill bits. High target sputtering power and sufficiently short target-to-substrate distance were found to be critical processing conditions. Very smooth (6.6 nm RMS surface roughness onto Si wafers) and hard AlMgB14 coatings enhance the hardness of WC-Co inserts and high-speed R6M5 steel by a factor of two and three, respectively. Complete coating spallation failure occurred at a scratch adhesion strength of 18 N. High work of adhesion and low friction coefficient, estimated for BAM onto drill bits, was as high as 64 J/m2 and as low as 0.07, respectively, more than twice the surpass characteristics of N-doped diamond-like carbon (DLC) films deposited onto nitride high-speed W6Mo5Cr4V2 steel.

Effects of La-Doped HfO2 Films on Dielectric Properties by Sol-Gel Method

HfO2 and La-doped HfO2 with 20, 40, 50, and 60 mol% were deposited on silicon wafers by spin-coating technique. The crystallization process was annealed temperature at 600 °C. Then, characterization techniques of XRD, AFM, SEM, Full-field XRF imaging, and XAS were applied to reveal structural morphology, local structure, grain, distribution, etc. This study aims to investigate the effect of doping La into the HfO2 system on surface formation, microstructure, and dielectric properties. According to the results, RMS surface roughness, and grain size increased relative to La concentration levels. These films demonstrated homogeneous, low surface roughness, and crack-free. The XRD confirms the existence of the monoclinic phase in pure HfO2 and the mixture phase of the monoclinic and orthorhombic phases in La-doped HfO2 films. Increasing La concentration caused the structural transformation, the XAS of La L3 -edge indicating that lanthanum remained in the HfO2 system. Dielectric response based on interface-phase polarization was improved with La content from 0 mol% to 60 mol%. Compared with HfO2 film, the dielectric constant of La-doped HfO2 films was increased and dielectric loss was decreased.

Pulsed laser deposition grown La0.3Ca0.7Fe0.7Cr0.3O3-δ thin films on yttria-stabilized zirconia substrates for fundamental electrochemical energy conversion studies

La0.3Ca0.7Fe0.7Cr0.3O3-δ (LCFCr) perovskites, normally deposited as a powder-based ink to form porous electrode layers, have been shown to be exceptional catalysts for the electrochemical splitting of CO2 to form CO at one electrode and O2 at the other during electrolysis in solid oxide cells, while also being highly active and stable under fuel cell conditions. This work constitutes the first report of thin film deposition of LCFCr via pulsed laser deposition on a 001-oriented yttria-stabilized zirconia substrate, used to simulate the ionically conducting electrolyte in operating cells. The primary goal of this work was to determine fundamental LCFCr properties and performance metrics without complications from morphology effects. Scanning Transmission Electron Microscopy and X-ray Photoelectron Spectroscopy analysis confirmed that oriented, dense, uniform, and smooth films with a thickness of ca. 25 nm and a RMS surface roughness of 0.2 nm are grown at 700 °C from a stoichiometric LCFCr target, while containing all the components of LCFCr in their expected oxidation states. These thin films have allowed the determination of the oxidation states of the redox active species on the electrode surface. Moreover, the preliminary electrochemical response of the LCFCr thin films in an air environment is shown to mimic the trends observed in more common highly porous LCFCr electrodes, thus arguing for a similar reaction mechanism and kinetics per real surface area.

Indium-zinc-oxide thin films produced by low-cost chemical solution deposition: Tuning the microstructure, optical and electrical properties with the processing conditions

Indium-zinc-oxide (IZO) films were prepared by spin coating an ethanol-ethylene-glycol precursor solution with a Zn/(In + Zn) ratio of 0.36 on glass. The effects of temperature on the structure, microstructure, electrical, and optical properties of the IZO thin films were investigated by thermal analysis, Fourier-transform infrared spectroscopy, X-ray diffraction, electron and atomic-force microscopy, X-ray photoelectron spectroscopy and variable-angle spectroscopic ellipsometry. The prepared IZO thin films heated at 500, 600, and 700 °C in air were transparent, without long-range ordering, and with an RMS surface roughness of less than 1 nm. The lowest electrical resistivity at room temperature, 0.0069 Ωcm, was observed for the 115-nm-thick IZO thin film heated at 600 °C in air and subsequently post-annealed in Ar/H2. The thin film exhibited a microstructure characterized by grains typically 20 nm in size and had no organic residues. This film exhibits uniaxial optical anisotropy due to its ultra-thin lamellae with a high electron density. The ordinary refractive index was fitted as a Tauc-Lorentz-Urbach function, which is typical of an indirect absorption edge occurring in amorphous semiconductor materials. The principal absorption peak with an onset at about 2.8 eV and a Tauc gap energy of ∼2.6 eV is similar to those observed for In2O3. The described process of chemical solution deposition and subsequent curing is promising for the low-cost fabrication of IZO thin films for transparent electronics, and can be used to tune the structure and microstructure of IZO thin films, as well as their electrical and optical properties.

Irradiation effect on structural and electrical properties of YMnO3/ITO/glass thin film

In this communication, the structural, microstructural and electrical properties of YMnO3/ITO/glass thin films have been thoroughly studied. Moreover, the electrical properties of this film have been studied in the absence of magnetic field and in the vicinity of applied magnetic field of 1 T. In addition to it, the YMnO3/ITO/glass thin films were grown using sophisticated pulsed laser deposition (PLD) technique which was further irradiated by 120 MeV Ag+9 ions with different ion fluence of 5 × 1011–5 × 1013 ions/cm2. In order to calculate crystallite size of the film, Scherrer’s formula and W-H plot are plotted. For the investigation of surface morphology, Atomic force microscopy (AFM) has been performed. Variation in electrical properties have been discussed in the context of average grain size, grain boundary density, rms surface roughness, defect density and oxygen vacancies. To understand the dielectric response of pristine and all the irradiated thin films under zero and 1 T applied magnetic fields, universal dielectric response (UDR) model and relaxation model have been fitted. Frequency dependent a.c. conductivity have been fitted by Jonscher’s power law and from its calculation maximum barrier height have been estimated. Average normalized constant (ANC), which provides the grain boundary density, have been analyzed from impedance data.

Bias-pulsed atomic layer etching of 4H-silicon carbide producing subangstrom surface roughness

A new approach to atomic layer etching (ALE) has been demonstrated, and its application to 4H-SiC is reported here. By pulsing only the DC bias for an Ar/Cl2 inductively coupled plasma-reactive ion etching system, the etch cycle duration is reduced by more than an order of magnitude relative to conventional ALE processes. Gas flows are not changed throughout the ALE process. With this process protocol, we achieved an etch rate of 2.48±0.09 Å/cycle with 6 s cycles, an RMS surface roughness (Rq) of 0.83±0.08 Å, and an ALE synergy value of S = 99%. The parameters explored within this ALE process demonstrate effective subangstrom smoothening of 4H-SiC surfaces and is well-suited for a variety of classical and quantum device nanofabrication.