Developments of elemental technologies to produce inch-size single-crystal diamond wafers

Seen as the future of wide band gap semiconductor materials, single-crystal diamonds need to be fabricated in at least inch-size wafers if they are to be of use in industry. The key methods required to achieve this are 1) improving the growth of single crystals with sufficient quality over large areas at an acceptable growth rate, 2) enlarging the seed crystal, and 3) improving the fabrication of the freestanding wafers. This paper briefly reviews recent progresses and reports the most recent results of our research of solving these technical problems.

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Research Highlights

► By using a lift-off process with ion implantation, we fabricated clone substrates. ► These clones are found to be useful to fabricate 1 inch mosaic wafers. ► The lift off process is applied also to make several clones of this 1 inch wafers. ► Some characterizations imply their quality is close to those of HPHT substrates.

Keywords

• Single-crystal-diamond; 
• Bulk-crystal-growth; 
• Freestanding wafer; 
• Simulation; 
• Mosaic wafer
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    • SOURCE:SCIENCEDIRECT
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Celebrating the 100th anniversary of the Stoney equation for film stress: Developments from polycrystalline steel strips to single crystal silicon wafers

Stress in a thin film on a flexible substrate induces a curvature of the substrate. Usually the substrate is orders of magnitude thicker than the film, leading to small and purely elastic deformation of the substrate. In this case, the Stoney equation yields the stress in the film from the measured curvature of the substrate. The Stoney equation contains thickness of film and substrate and the elastic properties of the substrate. Typically the elastic properties of the substrate are specified by E (Young's modulus), and ν (Poisson's ratio). E and ν provide a valid description for elastically isotropic substrates, e.g. polycrystalline steel strips, as used by Stoney in 1909.

Today the Stoney equation is still used for relating substrate curvature to film stress. However, in the majority of thin film stress measurements by means of substrate curvature, Si wafers are used as the substrate. Silicon wafers are cut from single crystals and are thereby elastically anisotropic. In the present paper, a modified form of the Stoney equation, well known for elastic isotropic substrates, is derived for Si(001) and Si(111) wafers, using the elastic stiffness constants of silicon, c_ij, instead of the orientation averaged values E and ν, which do not have a meaning for elastically anisotropic single crystal materials.

Curvature measurements of thin films on Si(001) and Si(111) wafers are presented. The difference in film-stress-induced curvature of Si(001) and Si(111) wafers is discussed.

Keywords

• Stress; 
• Thin film; 
• Coating; 
• Stoney; 
• Elastic anisotropy; 
• Silicon; 
• Wafer curvature
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• SOURCE:SCIENCEDIRECT
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Plastically deformed Ge-crystal wafers as elements for neutron focusing monochromator

Plastically deformed Ge-crystal wafers that have the cylindrical shape with a large curvature were characterized by neutron diffraction. The box-type rocking curve of Bragg reflection with the angular width ofΓ_box≃2°${}_{}\mathrm{}$ in FWHM, which is observable in the monochromatic neutron diffraction, results in an enhancement in the angle-integrated intensity (I_θ${}_{}$). Besides, I_θ${}_{}$ efficiently increases by stacking such Ge wafers. In the course of white neutron diffraction, the reflected-beam width near the focus point becomes sharper than the initial beam width. Further, the dependence of the horizontal beam width on the distance between the sample and detector is quantitatively explained by taking account of the large Γ_box${}_{}$, the small mosaic spread of η≃0.1°$\mathrm{}$, and the thickness of the wafers. On the basis of these characterizations, use of plastically deformed Ge wafers as elements for high-luminance neutron monochromator is proposed.

Keywords

• Plastically deformed Ge wafer; 
• Neutron monochromator crystal; 
• Neutron beam focus,crystal wafer,crystal wafer facebook,wafer crystal defects

• Source:Sciencedirect

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A high-performance bulk mode single crystal silicon microresonator based on a cavity-SOI wafer

Abstract

A cavity-silicon-on-insulator (SOI)-based single crystal silicon (SCS) micromechanical resonator has been demonstrated in this paper. The most distinguishing feature of this method is that it solves the restrictions of being released from the sacrificial layer. The resonator structures can be fabricated and released in one step using dry anisotropic etching. The differential drive, single-ended sense configuration is implemented to measure the electrical characterization of the fabricated resonator. The fabricated square plate resonator has been excited in the Lame´ mode at a resonant frequency of 4.126 MHz and exhibits a quality factor (Q) as high as 5.49× 10⁶ at a pressure of 0.05 mbar. This result corresponds to a frequency–Q product of 2.27× 10¹³, which is the highest value demonstrated to date for silicon-based resonators as far as we know. The dependence of Q and resonant frequency on the operating pressure is measured and characterized. The temperature stability of the device is also demonstrated, with the temperature coefficient of resonant frequency less than −20.8 ppm °C⁻¹ in the temperature range from −10 to 60 °C. The high performance of the resonator not only benefits from the superior performance of SCS as a mechanical material, but also the merit of the cavity-SOI structure.

Key words:
crystal sapphire wafer
single crystal wafer

wafer crystal defects

piezo crystal wafers

single crystal silicon wafer

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Two-channel IR gas sensor with two detectors based on LiTaO3 single-crystal wafer

Keywords

• LiTaO₃ wafer;
• Gas cell structure;
• Gas sensor

An infrared (IR) single-element detector based on a lithium tantalate (LiTaO₃) single-crystal wafer has been successfully fabricated. The preparation and design of the device are discussed and analyzed in detail. The processing of a thin LiTaO₃ wafer, the characterization of an IR filter window, and the assembly of the wafer and filter are explained. A LiTaO3 sensor element, a CMOS amplifier, a narrow-band filter (which can be selected to operate within the appropriate spectral region), and the read-out circuits are set into a TO-18 vessel. Each TO-18-type detector offers a single channel (a single detection wavelength). Two TO-18 detectors with different filters, one acting as a detection channel and the other as a reference, a broadband light source, a circuit board and a flake of wire gauze are assembled and integrated into a gilded gas cell for the purpose of detecting ethene gas.


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Uniform growth and repeatable fabrication of inch-sized wafers of a single-crystal diamond

We conducted a repetitive process for tiling freestanding substrates made from one identical seed crystal. After the mechanical polishing of both sides of the tiled substrates over the inch-sized area, the boundaries between the constituent substrates were barely recognized. By repeating the tiling process, we succeeded in fabricating several freestanding wafers with a size of 1.5 in. (area of approximately 20 × 40 mm2). For this wafer size range, we found that non-uniformities in the morphology, as well as the growth rate, became remarkable. By qualitative comparison between the numerical predictions and the experimental observations, we discussed the dominant factors that control the non-uniformity.

Highlights:
► Inch size wafers of single-crystal diamond are fabricated.
► Such large size wafers are processed to enlarge the wafer size moreover.
► Finally, 1.5 inch size freestanding wafers are fabricated.
► Possible reasons of non-uniformity in impurity concentration are discussed.

Keywords:
Single-crystal diamond; Microwave plasma CVD; Lift-off processing; Mosaic wafers; Simulation

More details....

Ammonothermal growth of high-quality GaN crystals on HVPE template seeds

High quality GaN crystals have been successfully grown by the ammonothermal method in alkaline ammonia solutions using hydride vapor phase epitaxy (HVPE) seeds. The grown crystals, over 1 mm thick, are clear and possess excellent structural and optical properties. The crystalline structure of the as-grown bulk GaN is as good as, or better than the HVPE seeds as measured by high resolution X-ray rocking curves with 100 arcsec of full width at half maximum (FWHM) on (0 0 2) and 90 arcsec on (1 0 2) diffractions. The crystal quality is improved through a process of careful seed selection and controlled heating during nucleation, so that the ammonothermal growth replicates the seed crystals on both the nitrogen and gallium faces. The results are confirmed by low temperature photoluminescence spectra resolving donor-bound and free excitons as well as multiple phonon replicas, and further by room temperature cathodoluminescence indicating reduced yellow-band emission. Successful growth of high quality GaN crystals on HVPE seeds will facilitate the scale-up to large area growth by use of large area GaN HVPE templates as seeds.

Source:IEEE

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Improved electrical properties of SiC wafer with defects covered by free standing graphene

As a single crystal SiC is grown, defects and dislocations occur due to many reasons. In particular, defects such as micropipes and micropores that are generated during the growth of single crystal SiC ingot have irregular locations and sizes. These defects continue to exist after the manufacturing process and undermine the properties of single crystal SiC wafer. Moreover, they lower the electrical properties of the wafers and can even cause detrimental damages after being applied in devices.

We combined single crystal SiC wafer and graphene with a floating method in order to use graphene as a bridge to connect the SiC bonding that is broken due to defects such as micropipes and micropores in single crystal SiC wafer. In this process, we characterized the layers of graphene needed, ranging from monolayer to multilayer, to cover micropipes and micropores of various sizes. As a result of measuring the thermoelectrical conductivity of single crystal SiC wafer combined with monolayer graphene up to temperatures of 400 °C, we observed electrical conductivity that was two or three orders higher than that of the SiC wafer alone. In addition, the connection between the SiC and the graphene was stable.

Highlights

• We covered defects in single crystal SiC with graphene using a floating method.

• Multi-μm sized defects in single crystal SiC were covered with monolayer graphene.

• We varied the number of graphene layers according to the sizes of the micropipes.

• The electrical conductivity of single crystal SiC wafer combined with graphene was improved.

• Graphene maintained its stable combination with single crystal SiC wafer at 400 °C.

Source:Diamond and Related Materials

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Production of large‐area single‐crystal wafers of cubic SiC for semiconductor devices

A reproducible process is described for growing a thick single‐crystal layer of cubic SiC on a single‐crystal Si wafer by chemical vapor deposition. A buffer layer, grown in situ, is used between the cubic SiC and the Si substrate to minimize the effect of lattice mismatch. Layers of up to 34 μm thick and several cm2 in area have been grown. Wafers are obtained by chemically removing the Si substrates from the grown layers. Excellent electron channeling patterns produced by these wafersindicate very good crystal quality. Preliminary electrical measurements have yielded electron mobilities up to 380 cm2/Vs.

Source:IEEE

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Photoelastic characterization of residual strain in MWA SI InP crystal wafers

A reproducible process is described for growing a thick single‐crystal layer of cubic SiC on a single‐crystal Si wafer by chemical vapor deposition. A buffer layer, grown in situ, is used between the cubic SiC and the Si substrate to minimize the effect of lattice mismatch. Layers of up to 34 μm thick and several cm2 in area have been grown. Wafers are obtained by chemically removing the Si substrates from the grown layers. Excellent electron channeling patterns produced by these wafers indicate very good crystal quality. Preliminary electrical measurements have yielded electron mobilities up to 380 cm2/Vs.

Source:IEEE

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Epitaxial high saturation magnetization FeN thin films on Fe(001) seeded GaAs(001) single crystal wafer using facing target sputterings

It was demonstrated that Fe–N martensite (α′) films were grown epitaxially on Fe(001) seeded GaAs(001) single crystal wafer by using a facing target sputtering method. X-ray diffraction pattern implies an increasing c lattice constant as the N concentration increases in the films. Partially ordered Fe16N2 films were synthesized after in situ post-annealing the as-sputtered samples with pure Fe8N phase. Multiple characterization techniques including XRD, XRR, TEM, and AES were used to determine the sample structure. The saturation magnetization of films with pure Fe8N phase measured by VSM was evaluated in the range of 2.0–2.2 T. The post annealed films show systematic and dramatic increase on the saturation magnetization, which possess an average value of 2.6 T. These observations support the existence of giant saturation magnetization in α″-Fe16N2 phase that is consistent with a recent proposed cluster-atom model and the first principles calculation.

Source:IEEE

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Nondestructive evaluation of large-area PZN-8%PT single crystal wafers for medical ultrasound imaging probe applications

It was demonstrated that Fe–N martensite (α′) films were grown epitaxially on Fe(001) seeded GaAs(001) single crystal wafer by using a facing target sputtering method. X-ray diffraction pattern implies an increasing c lattice constant as the N concentration increases in the films. Partially ordered Fe16N2 films were synthesized after in situ post-annealing the as-sputtered samples with pure Fe8N phase. Multiple characterization techniques including XRD, XRR, TEM, and AES were used to determine the sample structure. The saturation magnetization of films with pure Fe8N phase measured by VSM was evaluated in the range of 2.0–2.2 T. The post annealed films show systematic and dramatic increase on the saturation magnetization, which possess an average value of 2.6 T. These observations support the existence of giant saturation magnetization in α″-Fe16N2 phase that is consistent with a recent proposed cluster-atom model and the first principles calculation.

Source:IEEE

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300 mm silicon crystal growth and wafer processing

We have grown 300 mm silicon single crystals using a 28" hot zone with 200 kg charge size. The mechanical strength of silicon seeds was tested and a new style seed and chuck were developed for safer operation. Oxygen concentration and radial gradient (ORG) were controlled to ±2.5 ppma between 33 and 23 ppma and to less than 5% respectively. Crystal originated pit (COP) sizes were less than 0.15 μm. Wire saw technology has been used to slice the 300 mm wafers and the damage layer of the as-cut wafers investigated. The results show that wire sawn wafers have few defects. It has been found that rapid thermal annealing (RTA) can affect COP counts.

Source:IEEE

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Semi-insulating InP crystal wafers characterized by different nondestructive techniques

Nondestructive techniques of mapping of residual strain, photoluminescence and resistivity were utilized to optimize the multiple wafer annealing (MWA) procedure of undoped or slightly Fe doped InP crystal wafers under phosphorous atmosphere. The annealing procedure optimized did not additionally produce unwanted residual strain but reduced and homogenized it. In conclusion, MWA has proved to be a promising method to obtain semi-insulating InP crystals without undesired high Fe doping

Source:IEEE

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Growth of bulk GaN crystal by Na flux method under various conditions

High-quality and low cost bulk crystals are needed in the field of group III nitride semiconductors in order to develop optical and electrical devices. There are two approaches for the growth of bulk GaN crystal by the Na flux method. One is to grow thick GaN crystal on a large seed GaN crystal grown by vapor phase method. The other is to grow GaN crystal on a small seed GaN crystal. 3 in diameter GaN crystals were grown on the large GaN seed crystal. In the case of the growth on a small GaN seed, we obtained bulk crystal with a pyramidal shape and its height and diameter were 15 mm and >20 mm, respectively. We also present the effects of the impurity in the solution on the property and growth habit.

Source: Journal of Crystal Growth

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Reflection and transmission X-ray topographic study of a SiC crystal and epitaxial wafer

Defects in commercially available silicon carbide (SiC) wafers have been investigated by X-ray topography and optical microscopy. Dots appearing in transmission topographs are identified as a screw dislocation running through the [0001] direction by a comparative observation of the reflection topographs from the front and rear sides. In the peripheral region, these dots appear with high density and accompany large strain fields at the edge, which are related with the dislocations in the basal plane emanating from the dots and connecting them and large holes with diameters of about 10–20 μm opening at the epilayer surface. These large strain fields are considered to originate from the large Burgers vector associating with the screw dislocations.

Source: Materials Science and Engineering: B

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X-ray characterization of detached-grown germanium crystals

Germanium (1 1 1)-oriented crystals have been grown by the vertical Bridgman technique, in both detached and attached configurations. Microstructural characterization of these crystals has been performed using synchrotron white beam X-ray topography (SWBXT) and double axis X-ray diffraction. Dislocation densities were measured from X-ray topographs obtained using the reflection geometry. For detached-grown crystals, the dislocation density is on the order of 10⁴ cm⁻² in the seed region, and decreases in the direction of growth to less than 10³ cm⁻², and in some crystals reaches less than 10² cm⁻². For crystals grown in the attached configuration, dislocation densities were on the order of 10⁴ cm⁻² in the middle of the crystals, increasing to greater than 10⁵ cm⁻² near the edge. The measured dislocation densities are in excellent agreement with etch pit density (EPD) results. Broadening and splitting of the rocking curve linewidths was observed in the vicinity of subgrain boundaries identified by X-ray topography in some of the attached-grown crystal wafers. The spatial distribution of rocking curve linewidths across the wafers corresponds to the spatial distribution of defect densities measured in the X-ray topographs and EPD micrographs.

Source: Journal of Crystal Growth

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Prospects for the ammonothermal growth of large GaN crystal

The device technology for the wide-band-gap semiconductor group-III element nitrides (AlN, GaN, and InN) is much advanced over the growth of large-size, single-crystalline bulk material. In fact, lacking availability of thermal and lattice-matched substrates impedes the cost-effective fabrication of low-defect (low-loss) devices, which would bring a new quality in terms of device efficiency and lifetime. A promising route towards mass production of true bulk group-III element nitride crystal is the ammonothermal technique using supercritical ammonia under high-pressure conditions. Already demonstrated were the hydrothermal growth of a 3-in (0 0 0 1) ZnO crystal and, very recently, the first successful ammonothermal growth of a 1-in (0 0 0 1) GaN crystal. Based on the history of low-temperature SiO₂ and later ZnO growth by the hydrothermal technique, we report on recent achievements including solubility of GaN, and give an outlook for the growth of large-size GaN crystal by the ammonothermal route.

Source: Journal of Crystal Growth

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Silicon crystals for future requirements of 300 mm wafers

Today, the main challenge in Si crystal growth development is the transition from 200 to 300 mm diameter. While the complexity of the growth process increases with larger charge size and crystal diameter, the perfection of the growth process must significantly improve to avoid any disturbances that result in structure loss during growth and, hence, cause massive material losses. With regard to the future bulk quality, radical changes may be required as the design rule approaches the size of the prevailing grown-in defect type. Therefore, grown-in defect free wafers will be required, which can be produced either directly by pulling, by wafer annealing or by epitaxy. As substrates for annealed and epitaxial wafers, nitrogen doped and fast pulled crystals provide sufficient internal gettering capability in low thermal budget device processes. Moreover, grown-in defects in nitrogen doped crystals are so small that they are easily covered during epitaxy or annealed during high temperature treatment.

Source: Journal of Crystal Growth

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Correlation between energy deposition and AlN crystal growth induced by ion bombardment

A study has been made of the effects of ion (He, O, N and Ne) bombardment on the crystallization of AlN. AlN_0.8 thin films 100 nm thick were deposited on Si (111) wafers by an activated reactive evaporation method in a nitrogen atmosphere. He, O, N and Ne ions were bombarded onto films at room temperature to a dose of 5 × 10¹⁷ ions/cm², using an energy of 150 keV. This energy was chosen to place the average projected range of the ions in the substrate interior. XRD measurements were carried out using CuK α radiation (40 keV, 30 mA). The quantities of energy deposited in the films, through ionization and by recoil atoms, were calculated using TRIM-88. It is concluded that ion bombardment of AlN_0.8 thin films causes crystal growth of AlN, with the c-axis oriented perpendicular to the substrate plane, near to room temperature without any thermal annealing. Energy deposition through the ionization plays an essential role in the crystallization of AlN in AlNx thin films.

Source:sciencedirect

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Strain profiles and defect structure in 6H–SiC crystals implanted with 2 MeV As+ ions

Highly perfect (00.1) oriented 6H–SiC wafers were implanted with 2 MeV As⁺ ions to a number of fluencies in the range from 5 × 10¹² cm⁻² to 1 × 10¹⁴ cm⁻² and examined with synchrotron X-ray diffraction methods and RBS/channeling method. The X-ray methods included the investigation of rocking curves recorded with a small 50 × 50 μm² probe beam and white beam Bragg-Case section and projection topography.

The implanted layers provided distinct interference maxima in the rocking curves and interference fringes in Bragg-Case section topographies (strain modulation fringes). A good visibility of interference maxima enabled effective evaluation of the strain profile by fitting the theoretical rocking curves to the experimental ones. The evaluated strain profiles approximated by browsed Gaussian curves were similar to the distribution of point defects calculated with SRIM 2008 code. The profiles were similar to the defect distribution determined from the channeling measurements.

Source: Vacuum

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Etching study of dislocations in heavily nitrogen doped SiC crystals

Extensive study of threading dislocations in 4H SiC crystals has been carried out using etching in molten KOH. In contrast to well-defined hexagonal pits formed on lightly doped 4H epilayers, etching of bulk 4H SiC crystals heavily doped with nitrogen produced rounded etch pits with their sizes varying in a wide range. Neither shape nor size of the etch pits in the bulk n+4H crystals could be used to distinguish between threading edge and treading screw dislocations. Data on the density of threading screw dislocations were obtained by counting etch pits on the carbon face of the wafers.

Sequential steps of material removal, which included polishing followed by KOH etching, were used to track threading dislocations along the growth direction. It was found that a threading dislocation can produce etch pits of different sizes at different depths in the wafer.

Mobility of the front of threading dislocations during growth was assessed by measuring change in the position of the dislocation etch pits upon sequential material removal. Statistical distribution of such displacements in the wafer plane was found to be lognormal. On average, the growth distance of 8 μm corresponded to the change in the etch pit position of about 2 μm. This shows that the front of threading dislocations has significant mobility during SiC sublimation growth, resulting in tilted or curved dislocation lines in the grown crystal.

Source:Journal of Crystal Growth

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Growth and strain characterization of high quality GaN crystal by HVPE

Freestanding GaN crystals were fabricated by hydride vapor phase epitaxy using a random-islands facet-initiated epitaxial overgrowth technique. In this method, small micrometer sized GaN islands were firstly deposited on a TiC buffer layer on a sapphire substrate. Successive three-dimensional growth of GaN was controlled to a thickness of a few hundred micrometers on the buffer layer. Finally, a thick GaN layer was grown and high quality freestanding GaN crystals (dislocation density: <3×10⁶ cm⁻², radius of curvature: >5 m) were obtained by self-separation from the sapphire substrate. It was found that the dislocation density was drastically reduced in the initial growth stage of this method by the appearance of sidewall facets. Depth profiles of the residual strain in the freestanding GaN substrates have been successfully measured by a novel method employing cross-sectional micro-reflectance spectroscopy. It was found that the intrinsic strain, the driving force of wafer bending, can be greatly reduced by the introduction of three-dimensional growth in the initial growth stage.

Source:Journal of Crystal Growth

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Electrical properties and electrical field in depletion layer for CZT crystals

Current—voltage (I—V) and capacitance—voltage (C—V) characteristics of Au/p-CZT contacts with different surface treatments on cadmium zinc telluride (CZT) wafer's surface were measured with Agilent 4339B high resistance meter and Agilent 4294A precision impedance analyzer, respectively. The Schottky barrier height was 0.85±0.05, 0.96±0.05 eV for non-passivated and passivated CZT crystals by I—V measurement. By C—V measurement, the Schottky barrier height was 1.39±0.05, 1.51±0.05 eV for non-passivated and passivated CZT crystals. The results show that the passivation treatment can increase the barrier height of the Au/p-CZT contact and decrease the leakage current. The main reason is that the higher barrier height of Au/p-CZT contacts can decrease the possibility for electrons to pass through the native T_eO₂ film. Most of the applied voltage appears on the depleted layer and there is only a negligible voltage drops across the nearly undepleted region. Furthermore, the electric field in the depleted layer is not uniform and can be calculated by the depletion approximation. The maximum electric field of CZT crystals is E_ml=133 V/cm at x=0 for non-passivated CZT crystal and E_m2=55 V/cm for passivated CZT crystal, respectively.

Source: Transactions of Nonferrous Metals Society of China

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Observation of polytype stability in different-impurities-doped 6H–SiC crystals

The Al–B co-doped 6H–SiC and heavily N-doped 6H–SiC crystals grown by physical vapor transport method were investigated in this paper, respectively. The XPS (x-ray photoelectron spectroscope), Raman spectra analysis and XRD (X-ray diffraction) were applied to characterize the obtained SiC crystals. When the co-doping level with a ratio of B:Al = 0.22at.%:0.34at.% was obtained, Raman spectra results showed that there existed the 15R-polytype inclusion in the 6H–SiC crystal. When the co-doping ratio of B and Al increased to 1.18at.%:0.34at.%, there was only one polytype (6H) in the whole wafer. It can be speculated that the co-doping ratio of B:Al = 1.18at.%:0.34at.% may stabilize the crystal structure during the 6H–SiC crystal growth process. But the real mechanism of the polytype stability is unclear. The role of Al or B or other impurities to influence polytype stability will be further investigated in the future work. Moreover, it has been found that a high nitrogen doping level can influence the polytype stability during the 6H–SiC crystal growth process. And especially, the 4H-polytype is preferred.

Research Highlights

► 15R-polytype inclusion existed in the 6H-SiC crystal when B:Al=0.22at%:0.34at%.

► B:Al=1.18at%:0.34at% may stabilize crystal structure during 6H-SiC crystal growth.

► 4H-polytype is preferred in heavily nitrogen-doped 6H-SiC crystals.

Source:Diamond and Related Materials 

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Hierarchical Porous Patterns of n-type 6H–SiC Crystals via Photo-electrochemical Etching

Hierarchical porous patterns have been fabricated on the C face, Si face, and cross section of n-type 6H–SiC crystal via photo-electrochemical etching using HF/C₂H₅OH and HF/H₂O₂ as electrolytes. The porous layer displayed multiple and multiscale microstructures on different faces, including stalactite-like, sponge-like and dendritic porous structures on C face, echinoid micro-patterns on Si face, and columnar and keel-shaped micro-patterns on the cross section. The formation of hierarchical porous pattern is ascribed to the dynamic competition balance between the electrochemical oxidation rate and the oxide removal rate. It was found that increasing the ionic strength of the electrolyte can obviously disturb the surface morphology of the porous SiC during the photo-electrochemical etching. Possible mechanisms for selective etching were further discussed.

Source:Journal of Materials Science & Technology

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