Relationship of basal plane and prismatic stacking faults in GaN to low temperature photoluminescence peaks at ∼3.4 eV and ∼3.2 eV

2004 ◽  
Vol 831 ◽  
Author(s):  
J. Bai ◽  
M. Dudley ◽  
L. Chen ◽  
B. J. Skromme ◽  
P. J. Hartlieb ◽  
...  
Keyword(s):  
Low Temperature ◽  
Thin Layer ◽  
Basal Plane ◽  
Stacking Faults ◽  
Structural Defects ◽  
Cubic Phase ◽  
Bulk Crystals ◽  
Relationship Of ◽  
The Relationship ◽  
Low Temperature Photoluminescence

ABSTRACTThe relationship between the optical properties and microstructure of GaN is of great interest due to the important optical and electronic applications of this material. Several different studies have been reported attempting to link the low temperature photoluminescence (PL) peak at ∼3.4 eV to the presence of various microstructural defects. However, no clear systematic studies have been reported establishing such a link for the PL peak observed at ∼3.2 eV. In this paper, we present evidence linking the ∼3.4 eV PL peak to the presence of a thin layer of cubic phase associated with basal plane stacking faults (BSF). This relationship is mainly established by studying a series of ammonothermally-grown GaN bulk crystals. The existence and strength of the ∼3.4 eV peak are found to be related to the I2 type BSF (RI2=1/3<1>) observed in these samples. To investigate the relationship between the ∼3.2 eV peak and structural defects, a series of GaN epilayers grown on either SiC or sapphire (of various off-cut angles) was investigated by TEM and PL spectroscopy. Samples grown on 3.5° off-cut SiC and 5° and 9° off-cut sapphire substrates exhibit PL peaks near ∼3.2 and ∼3.4 eV, which are absent in the on-axis SiC and sapphire cases. TEM shows that the former group of samples has defect configurations consisting of prismatic stacking faults (PSFs) folding back and forth between two different {1120} planes connected by stair rod dislocations, which in turn fold onto to I1 type BSFs again with stair rod dislocations at the fault intersections. The ∼3.2 eV PL peaks are proposed to possibly arise from transitions involving the PSFs and the stair rods associated with their mutual intersections and their intersections with the BSFs. The ∼3.4 eV peak is again attributed to the thin layer of cubic phase associated with the I1 type BSF (three bilayers as opposed to four bilayers for the I2 type BSF).

Evaluation of Reflectance Fluorodensitometry for Measuring Aflatoxins on Thin Layer Plates

1971 ◽  
Vol 54 (4) ◽  
pp. 870-873
Author(s):  
Walter A Pons
Keyword(s):  
Thin Layer ◽  
Silica Gel ◽  
Uv Light ◽  
Plate Surface ◽  
Coefficients Of Variation ◽  
Standard Application ◽  
Tlc Plates ◽  
Relationship Of ◽  
The Relationship

Abstract A reflectance fluorodensitometer employing illumination of chromatograms with longwave UV light at 45° angles to the plate surface and measurement of reflected fluorescence at 90° was found to be suitable for measuring aflatoxins on silica gel-coated thin layer plates. The relationship of peak area vs. concentration was linear for 1–20 ng aflatoxins B1 and G1/ spot. Degradation of aflatoxins was slight. Five repetitive scans of the same chromatogram containing 5 ng each of B1 and G1 reduced the recorded areas an average of 1% per scan. Consecutive scans of 8 identical standard chromatograms containing 5 ng each of B1 and G1 and 1.5 ng each of B2 and G2 showed a reproducibility, as measured by coefficients of variation, of ±4–5% (B1 and G1) and ±5–9% (B2 and G2), representing the combined errors of standard application, TLC development, and scanning. Analysis of aflatoxins in purified sample extracts from 6 contaminated oilseed meals, 3–500 μg afla toxins/kg, in which the same TLC plates were scanned by a transmission densitometer and the reflectance densitometer yielded essentially equivalent values.

The Relationship of Growth Conditions to Structural Defects of LPE-ALXGa1-XSb

1991 ◽  
Vol 38-41 ◽  
pp. 917-922 ◽  
Author(s):  
Naritaka Kitamura ◽  
K. Higuchi ◽  
Masaya Ichimura ◽  
A. Usami ◽  
T. Wada
Keyword(s):  
Growth Conditions ◽  
Structural Defects ◽  
Relationship Of ◽  
The Relationship

The Effect of Different Doping Methods of Sintering Aids on the Barium Titanate Based X7R Ceramics

2007 ◽  
Vol 336-338 ◽  
pp. 83-86 ◽  
Author(s):  
C. Ma ◽  
X.H. Wang ◽  
R.Z. Chen ◽  
Long Tu Li ◽  
Zhi Lun Gui
Keyword(s):  
Rare Earth ◽  
Dielectric Loss ◽  
Barium Titanate ◽  
Low Temperature ◽  
Rare Earth Oxide ◽  
Sintering Aids ◽  
Sintering Properties ◽  
Relationship Of ◽  
The Relationship

The barium titanate based X7R ceramics, which are doped with rare earth oxide, Nb2O5, Co3O4 and ZnO-B2O3, could be sintered at a rather low temperature to satisfy the X7R requirements with good permittivity and dielectric loss. In this paper, different doping methods of sintering aids have been used to prepare X7R BaTiO3 ceramics. Samples were sintered at a low temperature and the relationship of doping methods and sintering properties has been concluded.

The Role of Impurities in LP-MOCVD Grown Gallium Nitride

1995 ◽  
Vol 395 ◽  
Author(s):  
C.Y. Hwang ◽  
Y. Li ◽  
M. J. Schurman ◽  
W. E. Mayo ◽  
Y. Lu ◽  
...  
Keyword(s):  
Gallium Nitride ◽  
Carrier Concentration ◽  
Electron Mobility ◽  
Structural Defects ◽  
Low Pressure Mocvd ◽  
Background Doping ◽  
Sims Analysis ◽  
Relationship Of ◽  
The Relationship

ABSTRACTWe have investigated the relationship of the Hall electron mobility to the background carrier concentration in low pressure MOCVD grown GaN. The highest electron mobility (400 cm2 /V•s) of the unintentionally doped GaN was obtained at a carrier concentration of 1×1017 cm−3 and samples with carrier concentrations lower than this exhibited lower mobilities. SIMS analysis shows C and O concentrations in the range of 2–3×1016 cm−3 and H in the 2–3×1017 cm−3 range. Structural defects, stoichiometry and impurities in the GaN films grown under different conditions are investigated to understand their relationship to the electron Hall mobilities. In particular, different growth temperatures and pressures were used to grow undoped GaN and modify the background doping effect of the impurities.

Defect Formation During Sublimation Bulk Crystal Growth of Silicon Carbide

1998 ◽  
Vol 510 ◽  
Author(s):  
Noboru Ohtani ◽  
Jun Takahashi ◽  
Masakazu Katsuno ◽  
Hirokatsu Yashiro ◽  
Masatoshi Kanaya
Keyword(s):  
Silicon Carbide ◽  
Crystal Growth ◽  
Defect Formation ◽  
Stacking Faults ◽  
Growth Direction ◽  
Bulk Crystal ◽  
Structural Defects ◽  
Bulk Crystals ◽  
Bulk Crystal Growth ◽  
Sublimation Growth

AbstractThe defect formation during sublimation bulk crystal growth of silicon carbide (SiC) is discussed. SiC bulk crystals are produced by seeded sublimation growth (modified-Lely method), where SiC source powder sublimes and is recrystallized on a slightly cooled seed crystal at uncommonly high temperatures (≥2000°C). The crystals contain structural defects such as micropipes (hollow core dislocations), subgrain boundaries, stacking faults and glide dislocations in the basal plane. The type and density of the defects largely depend on the crystal growth direction, and many aspects are different between the growth parallel and perpendicular to the <0001> c-axis. Micropipes are characteristic defects to the c-axis growth, while a large number of stacking faults are introduced during growth perpendicular to the c-axis. We discuss the cause and mechanism of the defect formation

scholarly journals STUDY ON TEMPERATURE FIELD OF ASYMMETRIC LARGE-SPAN ARCH SHEDS UNDER LOW-TEMPERATURE ENVIRONMENT

2020 ◽  
pp. 239-248
Author(s):  
Kai Zhou ◽  
Zhiwei Meng ◽  
Jialin Hou ◽  
Min Wei ◽  
Tianguo Jin ◽  
...  
Keyword(s):  
Temperature Distribution ◽  
Wind Speed ◽  
Low Temperature ◽  
Storage Capacity ◽  
Heat Storage ◽  
Large Span ◽  
Distribution Uniformity ◽  
Relationship Of ◽  
The Relationship ◽  
Better Than

In order to improve the effective sunshine time, heat storage capacity and temperature distribution uniformity of traditional arch shed under low temperature, this paper designed a large-span arch shed which has larger sunny side span and east-west orientation. According to the numerical and measured data, it is concluded that the heat storage capacity and temperature distribution of asymmetrical arch shed are better than those of symmetrical arch shed within a certain range of the ratio between sunny and shaded side. After that, ten different asymmetric arch sheds were designed. It is concluded that the structure of 11+9 m along north-south direction has the best heat storage capacity. Besides that, the analysis of outside wind speed and opening size of top vent were carried out. It is found that the outside wind and top vent can effectively promote convection and exchange of the air, and then achieve the purpose of reducing the temperature. At the end of this paper, in order to identify the relationship of temperature with the structure of arch shed, outside wind speed, and opening size of top vent, a mathematical model was built based on response surface methodology, which would provide theoretical guidance for the design of arch sheds.

Low-temperature photoluminescence of disordered thin-layer GaAs/AlAs superlattices: Experiment

1996 ◽  
Vol 53 (11) ◽  
pp. 7426-7433 ◽  
Author(s):  
Y. A. Zhang ◽  
J. A. Strozier ◽  
Alex Ignatiev
Keyword(s):  
Low Temperature ◽  
Thin Layer ◽  
Low Temperature Photoluminescence
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