A study of chemical beam epitaxy of GaAs using tris-dimethylaminoarsenic

The growth of GaAs by chemical beam epitaxy using triethylgallium and trisdimethylaminoarsenic has been studied. Reflection high-energy electron diffraction (RHEED) measurements were used to investigate the growth behavior of GaAs over a wide temperature range of 300–550°C. Both group III- and group Vinduced RHEED intensity oscillations were observed, and actual V/III incorporation ratios on the substrate surface were established. Thick GaAs epitaxial layers (2–3 μm) were grown at different substrate temperatures and V/III ratios, and were characterized by the standard van der Pauw-Hall effect measurement and secondary ion mass spectroscopy analysis. The samples grown at substrate temperatures above 490°C showed n-type conduction, while those grown at substrate temperatures below 480°C showed p-type conduction. At a substrate temperature between 490 and 510°C and a V/III ratio of about 1.6, the unintentional doping concentration is n ∼2 × 10¹⁵ cm⁻³ with an electron mobility of 5700 cm²/V·s at 300K and 40000 cm²/V·s at 77K.     

Thermal stability of heavily tellurium-doped InP grown by metalorganic molecular beam epitaxy

The thermal stability of tellurium in InP has been examined in samples doped with Te up to an electron concentration of 1.4 × 10²⁰ cm⁻³. Annealing was conducted using rapid thermal annealing for a period of one minute at temperatures over the range 650–800°C. Secondary ion mass spectroscopy analysis showed virtually no change in the Te profile before and after annealing, even at the highest annealing temperatures. High resolution x-ray diffraction and Hall measurements revealed a general decrease in the lattice strain and carrier concentration for annealing temperatures above 650°C. No evidence of strain relief was found in the form of cross-hatching or through the formation of a dislocation network as examined by scanning electron microscopy or transmission electron microscopy (TEM). These results are most likely due to the formation of Te clusters, though such clusters could not be seen by crosssectional TEM.     

The preparation of cryosections from plant tissue: An alternative method appropriate for secondary ion mass spectrometry studies of nutrient tracers and trace metals

A method involving cryostat sectioning (10 μm thickness) and freeze-drying is presented for the preparation of plant tissue for microanalytical studies. The method is well suited for semi-quantitative imaging by secondary ion mass spectrometry (SIMS) and offers significant advantages over bulk freeze-dried or freeze-substitution preparations. Segments of corn or soybean root (5 mm) are quench-frozen, embedded externally, sectioned in a cryostat (10 μm), pressed onto ultrapure Si and slowly freeze-dried. Images of these sections with secondary electron microscopy and SIMS indicated good morphological preservation. It was possible to section tissues of a wide developmental range, as well as roots varying sixfold in diameter. SIMS images are presented which demonstrate the ability to detect and localize nutrient tracers, such as Rb⁺, following brief exposures (10 min) to the intact plant. Likewise, a toxic metal (Al) was localized in root tissue after brief exposure (<1 day) of the intact plant root to micromolar external concentrations. Elemental redistribution during processing was minimal, as demonstrated most explicitly by the lack of movement of loosely bound Ca from the outer cell walls into the adjacent embedding material. Preservation of compositional differences between cellular content and cell wall was supported by a semi-quantitative treatment of SIMS images.     

Mode of arsenic incorporation in HgCdTe grown by MBE

The results of arsenic incorporation in HgCdTe layers grown by molecular beam epitaxy (MBE) are reported. Obtained results indicate that arsenic was successfully incorporated as acceptors in MBE-HgCdTe layers after a low temperature anneal. Secondary ion mass spectrometry and Hall effect measurements confirm that arsenic is incorporated with an activation yield of up to 100%. This work confirms that arsenic can be used as an effective dopant of MBE-HgCdTe after a low temperature annealing under Hg-saturated conditions.     

High-purity semi-insulating 4H-SiC grown by the seeded-sublimation method

The growth of high-purity, semi-insulating (HPSI) 4H-SiC crystals has been achieved using the seeded-sublimation growth technique. These semi-insulating (SI) crystals (2-inch diameter) were produced without the intentional introduction of elemental deep-level dopants, such as vanadium, and wafers cut from these crystals possess room-temperature resistivities greater than 10⁹ Ωcm. Based upon temperature-dependent resistivity measurements, the SI behavior is characterized by several activation energies ranging from 0.9–1.5 eV. Secondary ion mass spectroscopy (SIMS) and electron paramagnetic resonance (EPR) data suggest that the SI behavior originates from deep levels associated with intrinsic point defects. Typical micropipe densities for wafers were between 30 cm⁻² and 150 cm⁻². The room-temperature thermal conductivity of this material is near the theoretical maximum of 5 W/m K for 4H-SiC, making these wafers suitable for high-power microwave applications.     

BF_2~+注入多晶硅栅的SIMS分析

文本采用SIMS技术,分析了BF_2~+注入多晶硅栅退火前后F原子在多晶硅和SiO_2中的迁移特性。结果表明,80keV,2×10~(15)和5×10~(15)cm~(-2) BF_2~+注入多晶硅栅经过900℃,30min退火后,部分F原子已扩散到SiO_a中。F在多晶硅和SiO_2中的迁移行为呈现不规则的特性,这归因于损伤缺陷和键缺陷对F原子的富集作用。     

The influence of primary oxygen ions on SIMS depth profiling in materials implanted with cesium

The influence of implantation of oxygen as primary ions and cesium on SIMS in-depth profiles in an oxide glass was examined. For comparison samples of silicon and diamond film were used. Various behaviours of particular profiles were generally explained in terms of the chemical affinity of analysed reactants and an electric field created by implanted ions.     

采用二甲基肼为氮源进行GaNAs的金属有机化学气相沉积生长

采用MOCVD方法，利用二甲基肼为氮源，进行了GaNAs材料的生长。利用高分辨X射线衍射与二次离子质谱测试方法确定了材料中氮的组分。采用室温光致发光谱测量了样品的光学性质。讨论了不同的镓源对GaNAs材料质量和其中的杂质含量的影响，结果证明三乙基镓在GaNAs在低温生长中比三甲基镓具有更大的优势。采用三乙基镓生长的GaNAs中氮的含量达到5．688％。光致发光谱的峰值波长为1278．5nm。     

Anomalous temperature dependence of oxidation kinetics during steam oxidation of ferritic steels in the temperature range 550-650 °C

The oxidation behavior of a number of selected ferritic steels in a simulated steam environment at temperatures between 550 and 650 °C was studied. In the prevailing test gas, some of the studied 9-12% Cr steels tended to exhibit an anomalous temperature dependence of the oxidation behavior. This means, that the oxidation rates do not steadily increase with increasing temperature. At higher temperatures, some of the studied steels tend to form a very thin and protective oxide scale whereas at lower temperature rapidly growing, less-protective oxides are being developed. The anomalous temperature dependence is related to differences in chromium distribution in the inner part of the oxide scale. The effect is observed for steels with intermediate-Cr contents (∼10-12%) whereas steels with either lower or higher Cr contents exhibit an increasing oxidation rate with increasing temperature.     

SIMS and GDMS depth profile analysis of hard coatings

Rapid development in hard coating technology calls for simple construction depth profile analysers. Here we present results of depth profile analysis of a set of Ar arc plasma deposited TiN, CrN layers. The results are obtained with the use of recently constructed simple glow discharge mass spectrometer (GDMS) and compared with secondary ion mass spectrometer (SIMS). In SIMS (SAJW-05 model) we apply 5 keV Ar⁺ ion beam of about 100 μm in diameter. Digitally controlled spiral scanning of primary ion beam is performed over 1.6 mm² area. Secondary ions are extracted from the central part due to an “electronic gate” and analysed by quadrupole mass spectrometer QMA-410 Balzers (16 mm rods).GDMS analyses are performed on SMWJ-01 glow discharge prototype spectrometer. To supply discharge in 1 hPa argon we use 1.5 kV DC voltage. The analysed sample works as a cathode in a discharge cell. Area of the analysis is ∼4 mm² due to the use of secondary cathode—high purity tantalum diaphragm. Sputtered atoms are ionised, next extracted into the analytical chamber and finally analysed by the quadrupole mass analyser SRS-200 (6 mm rods).The results show that the use of simple construction GDMS analyser allows obtaining similar or even slightly better depth resolution than it can be obtained in the SIMS spectrometer. Application of glow discharge analysis opens new possibilities in direct quantitative depth profile analysis of hard coatings.