Conductivity Anisotropy in Epitaxial 6H and 4H Sic

1994 ◽  
Vol 339 ◽  
Author(s):  
William J. Schaffer ◽  
G. H. Negley ◽  
K. G. Irvine ◽  
J. W. Palmour
Keyword(s):  
High Temperature ◽  
Hall Mobility ◽  
Electron Mobility ◽  
Mobility Ratio ◽  
Apparent Temperature ◽  
Donor Level ◽  
Conductivity Anisotropy ◽  
High Quality ◽  
Total Impurity ◽  
Temperature Electron

ABSTRACTA measure of the electron mobility anisotropy in n-type 4H and 6H-SiC has been obtained using the Hall effect over the temperature range 80K<T<600K. Hall mobility and resistivity data are collected from appropriately oriented bar patterns fabricated into high quality epitaxial material grown on (1100) or (1120)surfaces having total impurity concentrations 1017-1018 cm-3. The observed mobility ratio for 4H is μ[1120]/[0001] and is independent of temperature. For 6H, the ratio μ[1100]/[0001] decreases from ∼6.2 at 80K to ∼5.0 at 150K and is essentially constant (∼4.8) above 200K. A donor level near 0.6 eV is occasionally observed in 4H which reduces the high temperature electron mobility and introduces an apparent temperature dependence to the mobility ratio if nonuniformly distributed.

Evidence of High Electron Mobility in CdGeAs2 Single Crystals

1999 ◽  
Vol 607 ◽  
Author(s):  
V.Yu. Rud' ◽  
Yu.V. Rud' ◽  
R. Pandey ◽  
M. C. Ohmer
Keyword(s):  
Low Temperature ◽  
Single Crystals ◽  
Hall Mobility ◽  
Electron Mobility ◽  
Phonon Scattering ◽  
High Electron ◽  
Growth Technique ◽  
Temperature Growth ◽  
Temperature Electron

AbstractCdGeAs2 single crystals were prepared by low temperature crystallization from a nonstoichiometric melt. The results of the first study of the temperature dependencies of the electrical conductivity and the Hall coefficient of n-type CdGeAs2 single crystals prepared by this new technique are reported. All the as-grown crystals show n-type conductivity. These single crystals had free electron concentrations of (1 - 2) 1018 cm−3 and Hall mobilities of more than 10000 cm2/(Vs) at T=300 K. These room temperature electron mobility values are four times larger than previously reported. In the high temperature region (T> 150K), the temperature dependence of the Hall mobility exhibited a behavior characteristic of phonon scattering. Below 150 K, a deviation from this behavior indicated an increasing contribution of static lattice defects to scattering. The Hall mobility in these crystals was found to reach ∼ 36000 cm2/( V· s ) at 77 K. The first photosensitive n-type CdGeAs2/n-type InSe heterostructures were constructed by contact methods. Photosensitivities of 70-100 V/were observed. This is substantially better than for previous structures using conventionally grown CdGeAs2 and indicates the high quality of the crystals. It is concluded that the low temperature growth technique is promising for the preparation of more perfect CdGeAs2crystals.

High-Temperature Synthesis of CdSe-Based Core/Shell, Core/Shell/Shell, and Core/Graded-Shell Nanoplatelets for Stable and Efficient Narrowband Emitters

2019 ◽  
Author(s):  
Aurelio A. Rossinelli ◽  
Henar Rojo ◽  
Aniket S. Mule ◽  
Marianne Aellen ◽  
Ario Cocina ◽  
...  
Keyword(s):  
Quantum Dots ◽  
High Temperature ◽  
Equilibrium Shape ◽  
Size Variation ◽  
Crystal Defects ◽  
Atomic Scale ◽  
Quantum Yields ◽  
Core Shell ◽  
Compositional Gradient ◽  
High Quality

<div>Colloidal semiconductor nanoplatelets exhibit exceptionally narrow photoluminescence spectra. This occurs because samples can be synthesized in which all nanoplatelets share the same atomic-scale thickness. As this dimension sets the emission wavelength, inhomogeneous linewidth broadening due to size variation, which is always present in samples of quasi-spherical nanocrystals (quantum dots), is essentially eliminated. Nanoplatelets thus offer improved, spectrally pure emitters for various applications. Unfortunately, due to their non-equilibrium shape, nanoplatelets also suffer from low photo-, chemical, and thermal stability, which limits their use. Moreover, their poor stability hampers the development of efficient synthesis protocols for adding high-quality protective inorganic shells, which are well known to improve the performance of quantum dots. <br></div><div>Herein, we report a general synthesis approach to highly emissive and stable core/shell nanoplatelets with various shell compositions, including CdSe/ZnS, CdSe/CdS/ZnS, CdSe/Cd<sub>x</sub>Zn<sub>1–x</sub>S, and CdSe/ZnSe. Motivated by previous work on quantum dots, we find that slow, high-temperature growth of shells containing a compositional gradient reduces strain-induced crystal defects and minimizes the emission linewidth while maintaining good surface passivation and nanocrystal uniformity. Indeed, our best core/shell nanoplatelets (CdSe/Cd<sub>x</sub>Zn<sub>1–x</sub>S) show photoluminescence quantum yields of 90% with linewidths as low as 56 meV (19.5 nm at 655 nm). To confirm the high quality of our different core/shell nanoplatelets for a specific application, we demonstrate their use as gain media in low-threshold ring lasers. More generally, the ability of our synthesis protocol to engineer high-quality shells can help further improve nanoplatelets for optoelectronic devices.</div>

scholarly journals Investigation of the Heteroepitaxial Process Optimization of Ge Layers on Si (001) by RPCVD

Nanomaterials ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 928
Author(s):  
Yong Du ◽  
Zhenzhen Kong ◽  
Muhammet Toprak ◽  
Guilei Wang ◽  
Yuanhao Miao ◽  
...  
Keyword(s):  
High Temperature ◽  
Buffer Layer ◽  
Layer Thickness ◽  
Growth Temperature ◽  
Crystalline Quality ◽  
Initial Growth ◽  
Two Dimensional ◽  
High Quality ◽  
Reduced Pressure

This work presents the growth of high-quality Ge epilayers on Si (001) substrates using a reduced pressure chemical vapor deposition (RPCVD) chamber. Based on the initial nucleation, a low temperature high temperature (LT-HT) two-step approach, we systematically investigate the nucleation time and surface topography, influence of a LT-Ge buffer layer thickness, a HT-Ge growth temperature, layer thickness, and high temperature thermal treatment on the morphological and crystalline quality of the Ge epilayers. It is also a unique study in the initial growth of Ge epitaxy; the start point of the experiments includes Stranski–Krastanov mode in which the Ge wet layer is initially formed and later the growth is developed to form nuclides. Afterwards, a two-dimensional Ge layer is formed from the coalescing of the nuclides. The evolution of the strain from the beginning stage of the growth up to the full Ge layer has been investigated. Material characterization results show that Ge epilayer with 400 nm LT-Ge buffer layer features at least the root mean square (RMS) value and it’s threading dislocation density (TDD) decreases by a factor of 2. In view of the 400 nm LT-Ge buffer layer, the 1000 nm Ge epilayer with HT-Ge growth temperature of 650 °C showed the best material quality, which is conducive to the merging of the crystals into a connected structure eventually forming a continuous and two-dimensional film. After increasing the thickness of Ge layer from 900 nm to 2000 nm, Ge surface roughness decreased first and then increased slowly (the RMS value for 1400 nm Ge layer was 0.81 nm). Finally, a high-temperature annealing process was carried out and high-quality Ge layer was obtained (TDD=2.78 × 107 cm−2). In addition, room temperature strong photoluminescence (PL) peak intensity and narrow full width at half maximum (11 meV) spectra further confirm the high crystalline quality of the Ge layer manufactured by this optimized process. This work highlights the inducing, increasing, and relaxing of the strain in the Ge buffer and the signature of the defect formation.

Low‐temperature electron mobility in InSb

1977 ◽  
Vol 48 (8) ◽  
pp. 3621-3622 ◽  
Author(s):  
B. R. Nag ◽  
G. M. Dutta
Keyword(s):  
Low Temperature ◽  
Electron Mobility ◽  
Temperature Electron

Comparative Study of GaN Growth Process by MOVPE

1999 ◽  
Vol 572 ◽  
Author(s):  
Jingxi Sun ◽  
J. M. Redwing ◽  
T. F. Kuech
Keyword(s):  
High Temperature ◽  
Comparative Study ◽  
Gas Phase ◽  
Residence Time ◽  
Gas Flow ◽  
Flow Sheet ◽  
Flow Zone ◽  
High Quality ◽  
Phase Temperature ◽  
High Temperature Gas

ABSTRACTA comparative study of two different MOVPE reactors used for GaN growth is presented. Computational fluid dynamics (CFD) was used to determine common gas phase and fluid flow behaviors within these reactors. This paper focuses on the common thermal fluid features of these two MOVPE reactors with different geometries and operating pressures that can grow device-quality GaN-based materials. Our study clearly shows that several growth conditions must be achieved in order to grow high quality GaN materials. The high-temperature gas flow zone must be limited to a very thin flow sheet above the susceptor, while the bulk gas phase temperature must be very low to prevent extensive pre-deposition reactions. These conditions lead to higher growth rates and improved material quality. A certain range of gas flow velocity inside the high-temperature gas flow zone is also required in order to minimize the residence time and improve the growth uniformity. These conditions can be achieved by the use of either a novel reactor structure such as a two-flow approach or by specific flow conditions. The quantitative ranges of flow velocities, gas phase temperature, and residence time required in these reactors to achieve high quality material and uniform growth are given.

scholarly journals The Progress on Low-Cost, High-Quality, High-Temperature Superconducting Tapes Deposited by the Combustion Chemical Vapor Deposition Process

2001 ◽  
Vol 689 ◽  
Author(s):  
Shara S. Shoup ◽  
Marvis K. White ◽  
Steve L. Krebs ◽  
Natalie Darnell ◽  
Adam C. King ◽  
...  
Keyword(s):  
Chemical Vapor Deposition ◽  
High Temperature ◽  
Critical Current Density ◽  
Buffer Layer ◽  
Critical Current ◽  
Vapor Deposition ◽  
Low Cost ◽  
Chemical Vapor ◽  
High Critical Current Density ◽  
High Quality

ABSTRACTThe innovative Combustion Chemical Vapor Deposition (CCVD) process is a non-vacuum technique that is being investigated to enable next generation products in several application areas including high-temperature superconductors (HTS). In combination with the Rolling Assisted Biaxially Textured Substrate (RABiTS) technology, the CCVD process has significant promise to provide low-cost, high-quality lengths of YBCO coated conductor. The CCVD technology has been used to deposit both buffer layer coatings as well as YBCO superconducting layers. A buffer layer architecture of strontium titanate and ceria have been deposited by CCVD on textured nickel substrates and optimized to appropriate thicknesses and microstructures to provide templates for growing PLD YBCO with high critical current density values. The CCVD buffer layers have been scaled to meter plus lengths with good epitaxial uniformity along the length. A short sample cut from one of the lengths enabled high critical current density PLD YBCO. Films of CCVD YBCO superconductors have been grown on single crystal substrates with critical current densities over 1 MA/cm2. Work is currently in progress to combine both the buffer layer and superconductor technologies to produce high-quality coupons of HTS tape made entirely by the non-vacuum CCVD process.

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