CrN Buffer Layer Research Articles

An investigation on microstructure and milling performance of arc-evaporated TiSin/AlTiN film

In this work, TiSiN/AlTiN multilayer film was deposited on cemented-carbide solid end mill tools by cathodic arc evaporation. The multilayer consisted of CrN buffer layer, Al0.67Ti0.33N adhesion layer, Ti0.9Si0.1N/Al0.67Ti0.33N alternate layer, and Ti0.9Si0.1N outlayer. An investigation on microstructure, mechanical properties, high-temperature wear rate, and milling performance of TiSiN/AlTiN multilayer film was conducted. The results indicate that the as-deposited TiSiN/AlTiN film exhibits a mixture phase of fcc-TiN and fcc-(Ti, Al)N. The hardness and elastic modulus of the TiSiN/AlTiN film are 41.7 ± 1.6 GPa and 340 ± 17 GPa, respectively. The wear rate of TiSiN/AlTiN film changes slightly when the experiment temperature is below 400°C, and then increases with the temperature increases to 600°C. Indentation hardness of TiSiN/AlTiN changes can be maintained above 40 GPa upon annealing to 800°C. However, the hardness of the film decreases from above 40 GPa to ⁓30.6 GPa when the annealing temperature increases to 1000°C. During dry milling, the TiSiN/AlTiN film reduces the adhesion between the coated tool and machined material SKD 11, leading to a low cutting force and cutting temperature.

Magnetization of Fe4N thin films: Suppression of interfacial intermixing using buffer layers

We studied the magnetization (Ms) of 60 nm thick polycrystalline Fe4N thin films deposited using reactive dc magnetron sputtering. The optimum substrate temperature (Ts) to grow an stoichiometric Fe4N phase is about 673 K, in agreement with earlier works. However, at this Ts, we found that significant intermixing is taking place at the substrate-film interface, affecting the Ms of Fe4N film, adversely. We performed secondary ion mass spectroscopy (SIMS) measurements to extract the extent of such intermixing. It was found that Si from the SiO2 substrate get interdiffused into Fe4N film forming an undesired interface extending up to almost half of the film. As a result, the average Ms of Fe4N film get reduced by about 25% as compared to its theoretical value. To prohibit such intermixing, we placed thin layers of Ag, Cu, or CrN as a buffer layer between the substrate and Fe4N film. Such buffer layer suppress the extent of interdiffusion remarkably. From SIMS measurements, we found that among all buffer layers, CrN is most suitable as it reduces the extent of intermixing to a minimum level. Magnetization measurements performed using bulk magnetization and polarized neutron reflectivity (PNR) methods also clearly revealed that the Ms was the highest when CrN buffer layer was used. From these results, it becomes apparent that the intermixing taking place at the substrate-film interface plays a vital role in affecting the Ms of Fe4N thin films. To further suppress such intermixing an attempt was also made to bring down the Ts from 673 to 523 K. Obtained results are presented and discussed in this work.

Polarity Determination of Polarity-Controlled ZnO Films Using Photoresponse Characteristics

We report on the use of the photoresponse characteristics of polarity- controlled ZnO films for determining ZnO polarity. ZnO films were grown on CrN and Cr2O3 buffer layers in order to produce Zn- and O-polar films, respectively, and Ti/Au metal contacts were formed. All samples showed Ohmic behavior, but the Zn-polar ZnO film showed lower contact resistance than the O-polar ZnO film. The O-polar ZnO film showed higher photocurrent and longer decay time than the Zn-polar film by photoresponse measurement. These phenomena can be explained by the expansion of the depletion layer into the bulk ZnO surface. Compared with current methods, this method of determination of the polarity of ZnO films through the measurement of photoresponse characteristics is very easy and simple to implement.

Growth of N-polar GaN Using a CrN buffer layer on (0001) Al2O3 via plasma-assisted molecular beam epitaxy

The growth of N-polar GaN films on (0001) Al2O3 substrates by plasma-assisted molecular beam epitaxy was demonstrated using a CrN buffer layer. Analysis of reflection high energy electron diffraction (RHEED) patterns and a chemical etching method were used in order to confirm the polarity of GaN on CrN. RHEED patterns show the 3×3 pattern characteristic of GaN. Chemical etching significantly changes the GaN surface morphology which implies that the N-polar GaN was grown on the CrN buffer layer. In addition, an improvement in the crystal properties of GaN was achieved using the annealing process for the CrN buffer layers.

Surface Polarity Effects on the Hydride Vapor Phase Epitaxial Growth of GaN on 6H-SiC with a Chrome Nitride Buffer Layer

A CrN buffer layer was introduced to 6H-SiC substrate to aid the subsequent hydride vapor phase epitaxial growth of GaN. Crystallinities of GaN layers grown on both Si- and C-terminated surfaces of 6H-SiC wafers with and without CrN layers were compared. On Si-terminated SiC, CrN formed with a trigonal morphology, indicating a good crystallographic relationship with growth along the 111 axis. CrN formed randomly on C-terminated SiC, leading to the subsequent GaN growth occurring with no preferred orientation, suggesting deteriorated crystallinity. High-quality GaN layers were grown on the CrN buffered Si-terminated SiC.

Epitaxial growth of GaN films on Cr‐compound buffer layers by plasma assisted molecular beam epitaxy

AbstractEpitaxial GaN layers were successfully grown on Al2O3 substrate with CrN buffer layer by plasma assisted molecular beam epitaxy (PA MBE). In order to form CrN layer, two kinds of formation methods are used such as nitridation of Cr‐metal and conventional MBE growth without extra process. With reflection high energy electron diffraction pattern analysis and x‐ray diffraction (XRD) measurement, it was confirmed that formed CrN layers have a cubic structured (111) CrN with single phase at all growth temperatures. Based on photoluminescence and XRD measurements, we suggest that the procedure of CrN buffer layer formation is more preferred the conventional MBE growth to nitrided Cr metal layer for GaN growth. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The thermal treatment effects of CrN buffer layer on crystal quality of Zn-polar ZnO films

We report on the annealing effects of CrN buffer layers on the crystal quality of Zn-polar ZnO films grown by plasma assisted molecular beam epitaxy. The high-temperature (HT) annealing of CrN buffer layer improved the crystallinity of ZnO films. The full width at half maximums of (0002) and (10–11) ZnO ω-scan X-ray diffraction show 574 and 1296 arcsec, respectively, which show the 3 and 2 times narrower values than those of ZnO films without the annealing process. Moreover, the HT annealing can be effective method to improve the surface smoothness of ZnO film and reduce the crystal tilting.

Growth of epitaxial ZnO films on Si (1 1 1) substrates with Cr compound buffer layer by plasma-assisted molecular beam epitaxy

Single crystalline ZnO film was grown on (1 1 1) Si substrate through employing an oxidized CrN buffer layer by plasma-assisted molecular beam epitaxy. Single crystalline characteristics were confirmed from in-situ reflection high energy electron diffraction, X-ray pole figure measurement, and transmission electron diffraction pattern, consistently. Epitaxial relationship between ZnO film and Si substrate is determined to be (0 0 0 1) ZnO‖(1 1 1) Si and [1 1 2¯ 0] ZnO‖[0 1 1] Si. Full-width at half-maximums (FWHMs) of (0 0 0 2) and (1 0 1¯ 1) X-ray rocking curves (XRCs) were 1.379° and 3.634°, respectively, which were significantly smaller than the FWHMs (4.532° and 32.8°, respectively) of the ZnO film grown directly on Si (1 1 1) substrate without any buffer. Total dislocation density in the top region of film was estimated to be ∼5×10 9 cm −2. Most of dislocations have a screw type component, which is different from the general cases of ZnO films with the major threading dislocations with an edge component.

Structural and stimulated emission characteristics of diameter-controlled ZnO nanowires using buffer structure

The diameter of ZnO nanowires grown by chemical vapour deposition was controlled by employing CrN buffer structures on the c-Al2O3 substrate. The nanosized CrN islands with different morphologies were prepared by nitridation of thickness-controlled Cr film in NH3 atmosphere. The ZnO nanowires grew normal to the surface of the CrN/c-Al2O3 templates due to reduction in the lattice mismatch between ZnO and c-Al2O3 by the CrN buffer layer. Investigation of the interface between CrN and ZnO by high resolution transmission electron microscopy revealed the presence of reactive layers such as ZnCr2O4 and Cr2O3. The diameter of nanowires significantly affected their stimulated emission characteristics. At room temperature, the threshold intensity for stimulated emission increased from 35 to above 500 kW cm−2 as the diameter of ZnO nanowires decreases from 223 to 77 nm. This dependence of threshold intensity for stimulated emission from nanowires is caused by an increase in the surface recombination and/or enhanced leakage of optical field in narrower nanowires.

Leakage current improvement of nitride-based light emitting diodes using CrN buffer layer and its vertical type application by chemical lift-off process

We report the electrical characteristics of vertical and lateral type light emitting diodes (LEDs) grown with CrN buffer layer. The LED with CrN buffer showed lower reverse leakage current than the reference sample grown with conventional low-temperature GaN buffer. It was also observed that the density of open core screw dislocation was smaller by one order of magnitude, which was thought to relate to the leakage current of devices. The vertical type LED fabricated by chemical etching of CrN buffer showed lower series resistance, lower turn-on voltage, and larger light output power than those of the conventional LEDs.

Fabrication of one-dimensional and two-dimensional periodically polarity inverted ZnO structures using the patterned CrN buffer layers

By employing the simple patterning and regrowth procedures, one-dimensional and two-dimensional (2D) periodically polarity inverted (PPI) ZnO structures are fabricated on (0001) Al2O3 substrates. For the selection of Zn- and O-polarity of ZnO films, patterned CrN buffer layers and Al2O3 substrates are used, respectively. The periodical change of the polarity is clearly confirmed by the polarity sensitive piezoresponse microscopy images, which are evidences for the successful fabrication of periodical polarity inversion structures. Cathodoluminescence investigation revealed that both polar layers have high crystal quality with strong free exciton emission. Moreover, 2D PPI ZnO structures with subnanometer scale periodicity are demonstrated by using the holographic lithography.

Chemical lift‐off of GaN epitaxial films grown on c‐sapphire substrates with CrN buffer layers

AbstractGaN epitaxial films are grown on c‐plane sapphire substrates with CrN buffer. The GaN layers show high crystalline quality and smooth surface morphology without being cracked. Selective etching of CrN buffer is performed by wet etching using conventional Cr metal etchant, which results in success ful lift‐off of GaN thick layers. We confirm that the crystalline quality of GaN does not change through the etching process. These results indicate that the chemical lift‐off process using CrN buffer is promising for production of both freestanding GaN substrates and vertical‐structure devices. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The Fabrication of Vertical Light-Emitting Diodes Using Chemical Lift-Off Process

Vertical light-emitting diodes (LEDs) were successfully fabricated by a chemical lift-off process using a selectively etchable CrN buffer layer. The novel CrN metallic layer worked well as a buffer layer for growth of the GaN LED and was etched out clearly during selective chemical etching. The vertical LED by chemical lift-off showed very good current-voltage performance with low series resistance of 0.65 Omega and low operated voltage of 3.11 V at 350 mA. Also, this device could be operated at a much higher injection forward current (1118 mA at 3.70 V) by thermally conductive metal substrate which enabled the high current operation with excellent heat dissipation.

Growth of Polarity-Controlled ZnO Films on (0001) Al2O3

The polarity control of ZnO films grown on (0001) Al2O3 substrates by plasma-assisted molecular-beam epitaxy (P-MBE) was achieved by using a novel CrN buffer layer. Zn-polar ZnO films were obtained by using a Zn-terminated CrN buffer layer, while O-polar ZnO films were achieved by using a Cr2O3 layer formed by O-plasma exposure of a CrN layer. The mechanism of polarity control was proposed. Optical and structural quality of ZnO films was characterized by high-resolution X-ray diffraction and photoluminescence (PL) spectroscopy. Low-temperature PL spectra of Zn-polar and O-polar samples show dominant bound exciton (I8) and strong free exciton emissions. Finally, one-dimensional periodic structures consisting of Zn-polar and O-polar ZnO films were simultaneously grown on the same substrate. The periodic inversion of polarity was confirmed in terms of growth rate, surface morphology, and piezo response microscopy (PRM) measurement.

The Growth of ZnO on CrN Buffer Layer Using Surface Phase Control by Plasma Assisted Molecular-beam Epitaxy

ABSTRACTEpitaxial ZnO films are successfully grown on Al2O3 substrates with phase controlled CrN buffer layer using Zn and O-plasma pre-exposures on CrN layers by plasma assisted molecular beam epitaxy (P-MBE). The Zn exposures on CrN layers prior to ZnO film growth result in the formation of rocksalt CrN without surface oxidation. On the other hand, the surface of the initially deposited CrN layers with rocksalt structure changes into hexagonal structured Cr2O3 after O-plasma exposure as confirmed by reflection high-energy electron diffraction (RHEED) and high resolution transmission electron microscopy (HR TEM). Etching studies show that the ZnO films grown on CrN have +C polarity, while the polarity of ZnO on Cr2O3/CrN double buffer is -C polarity. The interdiffusion of Zn and Cr occurs at the ZnO/CrN interface, while the interdiffusion is negligible at the ZnO/ Cr2O3 interface. The interdiffusion of Cr and Zn can be suppressed by inserting a low-temperature ZnO buffer layer in between ZnO and CrN layers, which helps improve the crystal quality of ZnO layers grown with CrN buffer.

Damage-free extreme ultraviolet mask with TaBN absorber

This article presents the results of evaluation of process-induced damage and improved reflectivity of an extreme ultraviolet (EUV) mask fabricated using a blank consisting of a multilayer, a Si capping layer, a CrN buffer layer, and a TaBN absorber. Long-term storage causes a centroid wavelength shift and stress change in the multilayer. The multilayer blank annealed at 90 °C was quite stable in centroid wavelength and film stress against resist baking at 135 °C and air storage. After the CrN buffer layer was etched with a mixture of Cl2 and O2 gases, the mask featured reflectivity loss of 1.5% due to the additional oxide layer generated on the Si capping layer. The reflectivity loss was able to be completely restored to its original value by treatment with a diluted HF solution. An EUV mask with a high reflectivity of 65% and excellent reflectivity uniformity of 0.7% 3σ was demonstrated using a blank consisting of a 40-period multilayer and a Si capping layer through a newly developed damage-free process that includes HF treatment.

Preparation and transport properties of Nb 1− xCr xN epitaxial thin films on silicon wafers

Nb 1− x Cr x N eptiaxial thin films were deposited on Si(0 0 1) and Si(1 1 1) substrates by molecular beam epitaxy of niobium nitride on a CrN buffer layer, followed by annealing at 973 K under nitrogen radical irradiation. X-ray photoelectron spectroscopy and X-ray diffraction measurements showed that on annealing the CrN buffer layer diffused into the niobium nitride layer to form Nb 1− x Cr x N films. The films showed superconductivity below 5–8 K. The temperature dependence of the resistivities above the transition temperatures were semiconductor-like, and varied on the orientation of the films.