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

If you need more information about X-ray characterization of detached-grown germanium crystals, please visit our website:http://www.powerwaywafer.com, send us email at powerwaymaterial@gmail.com.

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

If you need more information about Prospects for the ammonothermal growth of large GaN crystal, please visit our website:http://www.powerwaywafer.com, send us email at powerwaymaterial@gmail.com.

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

If you need more information about Silicon crystals for future requirements of 300 mm wafers, please visit our website:http://www.powerwaywafer.com, send us email at powerwaymaterial@gmail.com.

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

If you need more information about Correlation between energy deposition and AlN crystal growth induced by ion bombardment, please visit our website:http://www.powerwaywafer.com, send us email at powerwaymaterial@gmail.com.

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

If you need more information about Strain profiles and defect structure in 6H–SiC crystals implanted with 2 MeV As⁺ ions, please visit our website:http://www.powerwaywafer.com, send us email at powerwaymaterial@gmail.com.

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

If you need more information about Etching study of dislocations in heavily nitrogen doped SiC crystals, please visit our website:http://www.powerwaywafer.com, send us email at powerwaymaterial@gmail.com.

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

If you need more information about Growth and strain characterization of high quality GaN crystal by HVPE, please visit our website:http://www.powerwaywafer.com, send us email at powerwaymaterial@gmail.com.

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

If you need more information about Electrical properties and electrical field in depletion layer for CZT crystals, please visit our website:http://www.powerwaywafer.com, send us email at powerwaymaterial@gmail.com.

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 

If you need more information about Observation of polytype stability in different-impurities-doped 6H–SiC crystals, please visit our website:http://www.powerwaywafer.com, send us email at powerwaymaterial@gmail.com.