Gallium Nitride: An Overview of Structural Defects

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.

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Cathodoluminescence, Photoluminescence, and Optical Absorbance Spectroscopy of Aluminum Gallium Nitride (AlxGa1−xN) Films

Journal of Materials Research ◽

10.1557/jmr.1998.0348 ◽

1998 ◽

Vol 13 (9) ◽

pp. 2480-2497 ◽

Cited By ~ 8

Author(s):

Lawrence H. Robins ◽

Jeremiah R. Lowney ◽

Dennis K. Wickenden

Keyword(s):

Gallium Nitride ◽

Aluminum Gallium Nitride ◽

Deep Level ◽

Chemical Vapor ◽

Band Edge ◽

Structural Defects ◽

Excitation Mode ◽

Optical Absorbance ◽

Pl Spectra ◽

Film Substrate

Aluminum gallium nitride (AlxGa1−xN) films, grown by metalorganic chemical vapor deposition on sapphire, were characterized by low-temperature cathodoluminescence (CL) and photoluminescence (PL), and room-temperature optical absorbance. The aluminum fractions are estimated to range from x = 0 to x = 0.444. Most films were silicon-doped. The absorption spectra have a Urbach (exponential) form below the bandgap. The width of the Urbach edge, EU, increases with Al fraction, x, as EU = (0.045 +1 0.104x) eV. The luminescence (CL or PL) spectra show a relatively narrow band-edge peak and a broad deep-level peak. The full-widths at half-maximum of the band-edge CL peaks (measured at T = 15 K) are remarkably similar to the Urbach absorption widths, EU (measured at T = 300 K). PL spectra were obtained from the top surfaces and the film-substrate interfaces of several films. The interface PL spectra of some films show an extra peak 0.15 eV to 0.45 eV below the bandgap, which is ascribed to structural defects or impurity phases localized near the interface. The energy of the band-edge luminescence peak shifts with excitation mode (CL, top-surface PL, or interface PL). This effect is attributed to the variation of the excitation depth, between the top surface and film-substrate interface, with excitation mode, together with the depth variation of film properties such as residual stress or aluminum fraction.

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Transmission electron microscopy of composite materials

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100107125 ◽

1988 ◽

Vol 46 ◽

pp. 1012-1015

Author(s):

K.P.D. Lagerlof

Keyword(s):

Composite Materials ◽

Physical Properties ◽

Structural Defects ◽

Structural Composites ◽

Multiphase Materials ◽

Structural Reinforcement ◽

Transmission Electron ◽

Reinforced Fiber ◽

Particulate Reinforced Composites ◽

Definition Of

Although most materials contain more than one phase, and thus are multiphase materials, the definition of composite materials is commonly used to describe those materials containing more than one phase deliberately added to obtain certain desired physical properties. Composite materials are often classified according to their application, i.e. structural composites and electronic composites, but may also be classified according to the type of compounds making up the composite, i.e. metal/ceramic, ceramic/ceramie and metal/semiconductor composites. For structural composites it is also common to refer to the type of structural reinforcement; whisker-reinforced, fiber-reinforced, or particulate reinforced composites [1-4].For all types of composite materials, it is of fundamental importance to understand the relationship between the microstructure and the observed physical properties, and it is therefore vital to properly characterize the microstructure. The interfaces separating the different phases comprising the composite are of particular interest to understand. In structural composites the interface is often the weakest part, where fracture will nucleate, and in electronic composites structural defects at or near the interface will affect the critical electronic properties.

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High-angle electron scattering from amorphous silicon

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100137185 ◽

1995 ◽

Vol 53 ◽

pp. 162-163

Author(s):

M. Libera ◽

J.A. Ott ◽

K. Siangchaew ◽

L. Tsung

Keyword(s):

Electron Scattering ◽

Amorphous Material ◽

Structural Defects ◽

Constant Thickness ◽

High Angle ◽

Fast Electrons ◽

Angle Scattering ◽

Stem Image ◽

Amorphous Si ◽

Thermal Vibrations

Channeling occurs when fast electrons follow atomic strings in a crystal where there is a minimum in the potential energy (1). Channeling has a strong effect on high-angle scattering. Deviations in atomic position along a channel due to structural defects or thermal vibrations increase the probability of scattering (2-5). Since there are no extended channels in an amorphous material the question arises: for a given material with constant thickness, will the high-angle scattering be higher from a crystal or a glass?Figure la shows a HAADF STEM image collected using a Philips CM20 FEG TEM/STEM with inner and outer collection angles of 35mrad and lOOmrad. The specimen (6) was a cross section of singlecrystal Si containing: amorphous Si (region A), defective Si containing many stacking faults (B), two coherent Ge layers (CI; C2), and a contamination layer (D). CBED patterns (fig. lb), PEELS spectra, and HAADF signals (fig. lc) were collected at 106K and 300K along the indicated line.

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Silicon layers grown over SiO2 by liquid phase epitaxy: Electron Microscopical study

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010017596x ◽

1990 ◽

Vol 48 (4) ◽

pp. 566-567

Author(s):

F. Banhart ◽

F.O. Phillipp ◽

R. Bergmann ◽

E. Czech ◽

M. Konuma ◽

...

Keyword(s):

Electron Microscopy ◽

Liquid Phase ◽

Plasma Etching ◽

Liquid Phase Epitaxy ◽

Three Dimensional ◽

Microscopical Study ◽

Sample Temperature ◽

Structural Defects ◽

Si Substrates ◽

Etched Surface

Defect-free silicon layers grown on insulators (SOI) are an essential component for future three-dimensional integration of semiconductor devices. Liquid phase epitaxy (LPE) has proved to be a powerful technique to grow high quality SOI structures for devices and for basic physical research. Electron microscopy is indispensable for the development of the growth technique and reveals many interesting structural properties of these materials. Transmission and scanning electron microscopy can be applied to study growth mechanisms, structural defects, and the morphology of Si and SOI layers grown from metallic solutions of various compositions.The treatment of the Si substrates prior to the epitaxial growth described here is wet chemical etching and plasma etching with NF3 ions. At a sample temperature of 20°C the ion etched surface appeared rough (Fig. 1). Plasma etching at a sample temperature of −125°C, however, yields smooth and clean Si surfaces, and, in addition, high anisotropy (small side etching) and selectivity (low etch rate of SiO2) as shown in Fig. 2.

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DIGITAL IMAGING DETECTION AND IMAGE ANALYSIS OF INTERNAL STRUCTURAL DEFECTS IN GIS

Автометрия ◽

10.15372/aut20190609 ◽

2019 ◽

Keyword(s):

Image Analysis ◽

Digital Imaging ◽

Structural Defects ◽

Imaging Detection

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Dechannealing Study of Nanocrystalline Si:H Layers Produced by High Dose Hydrogen Irradiation of Silicon Crystals

MRS Proceedings ◽

10.1557/proc-536-499 ◽

1998 ◽

Vol 536 ◽

Author(s):

V. P. Popov ◽

A. K. Gutakovsky ◽

I. V. Antonova ◽

K. S. Zhuravlev ◽

E. V. Spesivtsev ◽

...

Keyword(s):

Electron Microscopy ◽

Transmission Electron Microscopy ◽

Rutherford Backscattering Spectrometry ◽

Nanocrystalline Structure ◽

Structural Defects ◽

High Dose ◽

Silicon Crystals ◽

Strong Energy ◽

Transmission Electron ◽

Hydrogen Implantation

AbstractA study of Si:H layers formed by high dose hydrogen implantation (up to 3x107cm-2) using pulsed beams with mean currents up 40 mA/cm2 was carried out in the present work. The Rutherford backscattering spectrometry (RBS), channeling of He ions, and transmission electron microscopy (TEM) were used to study the implanted silicon, and to identify the structural defects (a-Si islands and nanocrystallites). Implantation regimes used in this work lead to creation of the layers, which contain hydrogen concentrations higher than 15 at.% as well as the high defect concentrations. As a result, the nano- and microcavities that are created in the silicon fill with hydrogen. Annealing of this silicon removes the radiation defects and leads to a nanocrystalline structure of implanted layer. A strong energy dependence of dechanneling, connected with formation of quasi nanocrystallites, which have mutual small angle disorientation (<1.50), was found after moderate annealing in the range 200-500°C. The nanocrystalline regions are in the range of 2-4 nm were estimated on the basis of the suggested dechanneling model and transmission electron microscopy (TEM) measurements. Correlation between spectroscopic ellipsometry, visible photoluminescence, and sizes of nanocrystallites in hydrogenated nc-Si:H is observed.

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