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  • GaN substrate and GaN homo-epitaxy for LEDs: Progress and challenges

    2019-07-03

    After a brief review on the progresses in GaN substrates by ammonothermal method and Na-flux method and hydride vapor phase epitaxy (HVPE) technology, our research results of growing GaN thick layer by a gas flow-modulated HVPE, removing the GaN layer through an efficient self-separation process from sapphire substrate, and modifying the uniformity of multiple wafer growth are presented. The effects of surface morphology and defect behaviors on the GaN homo-epitaxial growth on free standing substrate are also discussed, and followed by the advances of LEDs on GaN substrates and prospects of their applications in solid state lighting. Source:IOPscience For more information, please visit our website: www.semiconductorwafers.net, send us email at sales@powerwaywafer.com or powerwaymaterial@gmail.com

  • The contact and photoconductivity characteristics between Co doped amorphous carbon and GaAs: n-type low-resistivity and semi-insulated high-resistivity GaAs

    2019-06-17

    The Co doped amorphous carbon films (a-C:Co), deposited by pulsed laser deposition, show p-n and ohmic contact characteristics with n-type low resistivity GaAs (L-GaAs) and semi-insulated high-resistivity GaAs (S-GaAs). The photosensitivity enhances for a-C:Co/L-GaAs, while inverse decreases for a-C:Co/S-GaAs heterojunction, respectively. Furthermore, the enhanced photosensitivity for the a-C:Co/L-GaAs/Ag heterojunction also shows deposition temperature dependence behavior, and the optimum deposition temperature is around 500 °C. Source:IOPscience For more information, please visit our website: www.semiconductorwafers.net, send us email at sales@powerwaywafer.com or powerwaymaterial@gmail.com

  • Realization and characterization of thin single crystal Ge films on sapphire

    2019-06-13

    We have successfully produced and characterized thin single crystal Ge films on sapphire substrates (GeOS). Such a GeOS template offers a cost-effective alternative to bulk germanium substrates for applications where only a thin (<2 µm) Ge layer is needed for device operation. The GeOS templates have been realized using the Smart CutTM technique. 100 mm diameter GeOS templates have been manufactured and characterized to compare the Ge thin film properties with bulk Ge. Surface defect inspection, SEM, AFM, defect etching, XRD and Raman spectroscopy were all performed. The results obtained for each characterization technique used have highlighted that the material properties of the transferred thin Ge film were very close to the ones of a bulk Ge reference. An epitaxial AlGaInP/GaInP/AlGaInP double heterostructure was grown atop the GeOS template to demonstrate the template's stability under the conditions encountered in typical device realization. The photoluminescent behavior of this epitaxial structure was nearly identical to that of a similar structure grown on a bulk Ge substrate. The GeOS templates therefore offer a viable alternative to bulk Ge substrates in the fabrication of devices whose operation is compatible with a thin film structure. Source:IOPscience For more information, please visit our website: www.semiconductorwafers.net, send us email at sales@powerwaywafer.com or powerwaymaterial@gmail.com

  • Optical nonlinearity characteristics of crystalline InSb semiconductor thin films

    2019-06-04

    The intensity-dependent nonlinear absorption and refraction characteristics of crystalline InSb thin films are investigated by z-scan method at 405 nm laser wavelength. Results show that the nonlinear absorption coefficient of crystalline InSb thin films is in the order of ~ + 10−2 m W−1, and the nonlinear refractive index is in the order of ~ + 10−9 m2 W−1. Variable-temperature ellipsometric spectroscopy measurements and electronic process analyses as well as theoretical calculations are employed to discuss the internal mechanisms responsible for the giant optical nonlinearity. Analysis results indicate that the nonlinear absorption mainly stems from the laser-induced free-carrier absorption effect, whereas the nonlinear refraction is mainly from thermal effect due to band gap shrinking and carrier effect due to the transition process of electrons, respectively. These characteristics may be responsible for the super-resolution effect in nano-optical information storage. Source:IOPscience For more information, please visit our website: www.semiconductorwafers.net, send us email at sales@powerwaywafer.com or powerwaymaterial@gmail.com

  • Study of a double epi-layers SiC junction barrier Schottky rectifiers embedded P layer in the drift region

    2019-05-27

    This paper proposes a double epi-layers 4H–SiC junction barrier Schottky rectifier (JBSR) with embedded P layer (EPL) in the drift region. The structure is characterized by the P-type layer formed in the n-type drift layer by epitaxial overgrowth process. The electric field and potential distribution are changed due to the buried P-layer, resulting in a high breakdown voltage (BV) and low specific on-resistance (Ron,sp). The influences of device parameters, such as the depth of the embedded P+ regions, the space between them and the doping concentration of the drift region, etc., on BV and Ron,sp are investigated by simulations, which provides a particularly useful guideline for the optimal design of the device. The results indicate that BV is increased by 48.5% and Baliga's figure of merit (BFOM) is increased by 67.9% compared to a conventional 4H–SiC JBSR. Source:IOPscience For more information, please visit our website: www.semiconductorwafers.net, send us email at sales@powerwaywafer.com or powerwaymaterial@gmail.com

  • Growth of InP directly on Si by corrugated epitaxial lateral overgrowth

    2019-05-23

    In an attempt to achieve an InP–Si heterointerface, a new and generic method, the corrugated epitaxial lateral overgrowth (CELOG) technique in a hydride vapor phase epitaxy reactor, was studied. An InP seed layer on Si (0 0 1) was patterned into closely spaced etched mesa stripes, revealing the Si surface in between them. The surface with the mesa stripes resembles a corrugated surface. The top and sidewalls of the mesa stripes were then covered by a SiO2 mask after which the line openings on top of the mesa stripes were patterned. Growth of InP was performed on this corrugated surface. It is shown that growth of InP emerges selectively from the openings and not on the exposed silicon surface, but gradually spreads laterally to create a direct interface with the silicon, hence the name CELOG. We study the growth behavior using growth parameters. The lateral growth is bounded by high index boundary planes of {3 3 1} and {2 1 1}. The atomic arrangement of these planes, crystallographic orientation dependent dopant incorporation and gas phase supersaturation are shown to affect the extent of lateral growth. A lateral to vertical growth rate ratio as large as 3.6 is achieved. X-ray diffraction studies confirm substantial crystalline quality improvement of the CELOG InP compared to the InP seed layer. Transmission electron microscopy studies reveal the formation of a direct InP–Si heterointerface by CELOG without threading dislocations. While CELOG is shown to avoid dislocations that could arise due to the large lattice mismatch (8%) between InP and Si, staking faults could be seen in the layer. These are probably created by the surface roughness of the Si surface or SiO2 mask which in turn would have been a consequence of the initial process treatments. The direct InP–Si heterointerface can find applications in high efficiency and cost-effective Si based III–V semiconductor multijunction solar cells and optoelectronics integration. Source:IOPscience For more information, please visit our website: www.semiconductorwafers.net, send us email at sales@powerwaywafer.com or powerwaymaterial@gmail.com

  • Charge transport performance of high resistivity CdZnTe crystals doped with In/Al

    2019-05-13

    To evaluate the charge transport properties of as-grown high resistivity CdZnTe crystals doped with In/Al, the α particle spectroscopic response was measured using an un-collimated 241Am (5.48 MeV) radioactive source at room temperature. The electron mobility lifetime products (μτ)e of the CdZnTe crystals were predicted by fitting plots of photo-peak position versus electrical field strength using the single carrier Hecht equation. A TOF technique was employed to evaluate the electron mobility for CdZnTe crystals. The mobility was obtained by fitting the electron drift velocities as a function of the electrical field strengths, where the drift velocities were achieved by analyzing the rise-time distributions of the voltage pulses formed by a preamplifier. A fabricated CdZnTe planar detector based on a low In concentration doped CdZnTe crystal with (μτ)e = 2.3 × 10−3 cm2/V and μe = 1000 cm2/(V dot m s), respectively, exhibits an excellent γ-ray spectral resolution of 6.4% (FWHM = 3.8 keV) for an un-collimated 241Am @ 59.54 keV isotope. Source:IOPscience For more information, please visit our website: www.semiconductorwafers.net, send us email at sales@powerwaywafer.com or powerwaymaterial@gmail.com

  • Selective-area growth of GaN on non- and semi-polar bulk GaN substrates

    2019-05-09

    We carried out the selective-area growth of GaN and fabricated InGaN/GaN MQWs on non- and semi-polar bulk GaN substrates by MOVPE. The differences in the GaN structures and the In incorporation of InGaN/GaN MQWs grown on non- and semi-polar GaN substrates were investigated. In the case of selective-area growth, different GaN structures were obtained on GaN,  GaN, and GaN substrates. A repeating pattern of  and  facets appeared on  GaN. Then, we fabricated InGaN/GaN MQWs on the facet structures on  GaN. The emission properties characterized by cathodoluminescence were different for  and  facets. On the other hand, for InGaN/GaN MQWs on non- and semi-polar GaN substrates, steps along the a-axis were observed by AFM. In particular on  GaN, undulations and undulation bunching appeared. Photoluminescence characterization indicated that In incorporation increased with the off-angle from the m-plane and also depended on the polarity. Source:IOPscience For more information, please visit our website: www.semiconductorwafers.net, send us email at sales@powerwaywafer.com or powerwaymaterial@gmail.com

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