Parasitic reaction and its effect on the growth rate of AlN by metalorganic chemical vapor deposition

The Al composition of metalorganic chemical vapor deposition (MOCVD)-grown AlGaN alloy layers is found to be greatly influenced by the parasitic reaction between ammonia (NH3) and trimethylaluminum (TMAI). The growth process of AlN is carefully investigated by monitoring the in situ optical reflection. The abnormal dependencies of growth rate on growth temperature, reactor pressure, and flux of NH3 are observed and can be well explained by the effect of parasitic reaction. The increase of growth rate with increasing flux of TMAI is found to depend on the growth temperature and reactor pressure due to the presence of parasitic effect. A relatively low growth temperature and a reduced reactor pressure are suggested for the effective decrease of parasitic reaction during the MOCVD growth of AlN and probably lead to a more effective incorporation of Al into the AlGaN layers. (c) 2005 Elsevier B.V. All rights reserved.

Preparation and characterization of GaN films by radio frequency magnetron sputtering and carbonized-reaction technique

Radio frequency magnetron sputtering/post-carbonized-reaction technique was adopted to prepare good-quality GaN films on Al2O3(0 0 0 1) substrates. The sputtered Ga2O3 film doped with carbon was used as the precursor for GaN growth. X-ray diffraction (XRD) pattern reveals that the film consists of hexagonal wurtzite GaN. X-ray photoelectron spectroscopy (XPS) shows that no oxygen can be detected. Electrical and room-temperature photoluminescence measurements show that good-quality polycrystalline GaN films were successfully grown on Al2O3(0 0 0 1) substrates. (c) 2005 Elsevier B.V. All rights reserved.

SiO2/Ta interface reaction in magnetic multilayers and its influence on Ta buffer layers

Ta is often used as a buffer layer in magnetic multilayers. In this study, Ta/Ni81Fe19/Ta multilayers were deposited by magnetron sputtering on sing-crystal Si with a 300-nm-thick SiO2 film. The composition and chemical states at the interface region of SiO2/Ta were studied using the X-ray photoelectron spectroscopy (XPS) and peak decomposition technique. The results show that there is an 'inter-mixing layer" at the SiO2/Ta interface due to a thermodynamically favorable reaction: 15 SiO2 + 37 Ta = 6 Ta2O5 + 5 Ta5Si3. Therefore, the Ta buffer layer thickness used to induce NiFe (111) texture increases.

Compatibility relationship among reaction equilibria, equivalence principle of reaction approaches, and silicon contamination in semiconductors

This paper discovers some shortcomings in the algorithm for the incorporation of Si into GaAs in the GaAs VPE process. These faults arise from neglecting a link, the compatibility relationship, in chemical thermodynamics. The meaning of said relationship is as follows: In an equilibrium complex system, each species can only contribute one and the same quantity (its equilibrium quantity) to the different equilibria of the various reactions involving it; yet even under this restriction, every equilibrium constant is satisfied, and all the reaction equilibria coexist compatibly in the system. Only by adding the relationship can the equilibrium theory for the complex system be complete. This paper also tells its position in chemical thermodynamics. Such a compatibility concept directly leads to an equivalence principle: In a complex system, a certain species can usually be simultaneously formed by many chemical reactions; when the system has reached equilibrium under fixed environmental conditions, the equilibrium quantity of said species calculated according to each chemical equation of these reactions will be equal and the various reaction approaches will be equivalent, provided that for all the reactants and all the other products of these reactions their equilibrium quantities in the system are respectively taken as corresponding knowns for the calculations, which is extremely useful for seeking a functional relation among the species' equilibrium quantities in a system (Si contamination is one of the examples). Under the guidance of those arguments, the various schools' algorithms for the Si contamination can be uniformized and simplified, and the contamination quantity relation between Si and O, two very important impurities, is found.

Identification of induced reaction during XPS depth profile measurements of CeO2/Si films grown by ion beam epitaxy

An anomalous behavior was observed in X-ray photoelectron Spectroscopy (XPS) depth profile measurements conducted on CeO2/Si epilayers grown by ion beam epitaxy (IBE): the signals of Ce3+ and Ce4+ co-exist, and the ratio between them increases during the etching time and then tends to maintain a constant level before increasing again. The results of X-ray Diffraction (XRD), Auger Electron Spectroscopy (AES), and Rutherford Back-Scattering (RES) measurements proved that the reduction chemical reaction of CeO2 is induced by ion-etching. (C) 1998 Elsevier Science Ltd. All rights reserved.

Mechanism of induced reaction during XPS depth profile measurements of CeO2/Si films grown by ion beam epitaxy

In a search for the mechanism of the induced reduction reaction that occurred in X-ray photoelectron Spectroscopy (XPS) depth profiles measured experimentally on CeO2/Si epilayers grown by ion beam epitaxy (IBE), several possibilities have been checked. The first possibility, that the X-ray induces the reaction, has been ruled out by experimentation. Other possible models for the incident-ion induced reaction, one based on short-range interaction (direct collision) and the other based on long-range potential accompanied with the incident-ions, have been tested by simulation on computer. The results proved that the main mechanism is the former, not the latter. (C) 1998 Elsevier Science Ltd. All rights reserved.

Continuous-flow polymerase chain reaction microfluidics by using spiral capillary channel embedded on copper

This paper presents a novel method for performing polymerase chain reaction (PCR) amplification by using spiral channel fabricated on copper where a transparent polytetrafluoroethylene ( PTFE) capillary tube was embedded. The channel with 25 PCR cycles was gradually developed in a spiral manner from inner to outer. The durations of PCR mixture at the denaturation, annealing and extension zones were gradually lengthened at a given flow rate, which may benefit continuous-flow PCR amplification as the synthesis ability of the Taq polymerase enzyme usually weakens with PCR time. Successful continuous-flow amplification of DNA fragments has been demonstrated. The PCR products of 249, 500 and 982 bp fragments could be obviously observed when the flow rates of PCR mixture were 7.5, 7.5 and 3.0 mm s(-1), respectively, and the required amplification times were about 25, 25, and 62 min, respectively. Besides, the successful segmented-flow PCR of three samples ( 249, 500 and 982 bp) has also been reported, which demonstrates the present continuous-flow PCR microfluidics can be developed for high-throughput genetic analysis.