Study Of Defects In Semiconductors Research Articles

Photo-induced electron paramagnetic resonance: A means to identify defects and the defect level throughout the bandgap of ultrawide bandgap semiconductors

Ultrawide bandgap semiconductors (UWBGs) provide great promise for optical devices operating in the near to deep ultraviolet, and recently they have become a viable semiconducting material for high power electronics. From the power grid to electronic vehicles, the intention is to replace massively awkward components with the convenience of a solid state electronic “chip.” Unfortunately, the challenges faced by wide bandgap electronic materials, such as GaN and SiC, increase as the bandgap increases. A point defect, for example, can take on more charge states and energy configurations. This perspective describes a method to investigate the many charge states and their associated transitions—photo-induced electron paramagnetic resonance (photo-EPR) spectroscopy. Although not new to the study of defects in semiconductors, photo-EPR studies can probe the entire ultrawide bandgap given the appropriate light source for excitation. Examples provided here cover specific defects in UWBGs, AlN, and Ga2O3. The discussion also reminds us how the rapid pace of discovery surrounding this newest class of semiconductors is due, in part, to fundamental research studies of the past, some as far back as a century ago and some based on very different materials systems.

Doppler Broadening Spectroscopy of Positron Annihilation near Ge and Si (001) Single Crystal Surfaces

carrier mobility compared with Si. 1 Although closely related to Si, in some aspects Ge shows a quite different behavior. This should be taken into account when processing steps are developed for the production of electronic devices with active Ge layers, in which the Ge layer surfaces and interfaces will play an important role. 2 In this letter, we investigated the effect of the free (001) surface on positron annihilation spectroscopy (PAS) results, comparing Si and Ge substrates. PAS is a powerful tool for the study of vacancy-type defects in semiconductors, 3,4 e.g. in irradiated Si and Ge. Positron trapping at vacancies can be observed by the narrowing of the Doppler-broadened 511 keV annihilation γ-ray peak. By varying the incident positron energy, one can probe different sample depths in the submicron range. This method is called Doppler Broadening Spectroscopy (DBS). The so called S-parameter, extracted from DBS, corresponds to positron annihilation by the valence electrons and is sensitive to open volume defects. An increase of the S-parameter can be simply interpreted as an increase of the number of vacancy-type defects. The S-parameter obtained for an incident positron energy lower than 2 keV, however, in general differs from the one obtained for positron energies above 15 keV. Incident positrons with lower energy will indeed mainly interact with the near surface area of the sample, and will be sensitive for thin native oxide layers, surface contamination, surface roughness, surface defects, etc. The S-parameter decreases in general toward the surface for most materials due to positron diffusion toward and annihilation at the surface. 5 The present letter reports on the different behavior of Si and Ge with this respect. While in case of Si, the S-parameter decreases considerably near the Si (001) surface as expected and as is the case for other semiconductor materials, in the case of a Ge (001) surface, the S-parameter shows no remarkable dependence on depth although both are group IV elements and have the same diamond structure. For the PAS measurements, moderately doped p-type Si and n-type Ge (001) wafers were used with a resistivity at room temperature in the range of 10–100 ohm corresponding with a carrier concentration at room temperature in the range of 10 13 ∼10 15 cm −3 . As a reference for the Si bulk and at the same time the near surface of Ge, a Geon-Insulator (GOI) wafer with a un-doped Ge top-layer produced by the Ge condensation technique, was also included in the study. The carrier concentration in the n-type Ge film of the GOI wafer that

Importance of the correct Fermi energy on the calculation of defect formation energies in semiconductors

Density functional theory (DFT) is a major theoretical tool for the study of defects in semiconductors. However, the results suffer from the often too-small DFT band gap. The calculation of defect formation energy (ΔH) using more sophisticated DFT+GW and hybrid functional methods, however, suggest qualitatively different conclusions about the nature of the DFT error. Here we show that these discrepancies originate from large differences in the representation of the Fermi energy of bulk for the different methods and that they can be largely brought into agreement by correcting the DFT ionization energy.

Ion Beam Analysis: A Century of Exploiting the Electronic and Nuclear Structure of the Atom for Materials Characterisation

Analysis using MeV ion beams is a thin film characterisation technique invented some 50 years ago which has recently had the benefit of a number of important advances. This review will cover damage profiling in crystals including studies of defects in semiconductors, surface studies, and depth profiling with sputtering. But it will concentrate on thin film depth profiling using Rutherford backscattering, particle induced X-ray emission and related techniques in the deliberately synergistic way that has only recently become possible. In this review of these new developments, we will show how this integrated approach, which we might call "total IBA", has given the technique great analytical power.

Local cathodoluminescence study of defects in semiconductors and multilayer structures

Abstract Local cathodoluminescence (CL) method gives a lot of new possibilities comparing with photoluminescence. One of the most important features of the cathodoluminescent method is possibility of depth examination of semiconductor structure emission properties from 10 nm up to several microns. This permits one to study the luminescent properties in depth, to define the value diffusion length of charge carrier in the structures, to characterize carrier transport properties of the multilayer structures, to determine the presence and the activation energy of the electron traps. These CL features were used for studying multilayer structures based on InAlGaN and A III B V .

Ab initio modeling of defect levels in Ge clusters and supercells

Most density-functional studies of defects in semiconductors invariably use (i) a supercell that imitates the host crystal, as well as (ii) a local treatment of the exchange-correlation potential. The first approximation has had an enormous success in many materials, provided that the size of cell is large enough to minimize long-range interactions between the infinite lattice of defects. For instance, these may arise from strain fields or from the overlap between shallow defect states. The second approximation, when combined with the periodic boundary conditions, leads to an essentially metallic density of states in Ge, which can compromise any investigation of electronic transitions involving gap levels. Here, we report on two approaches to surmount these difficulties, namely (i) to open the gap by reducing the host to a Ge cluster of atoms whose states are confined by a surface potential and (ii) to use supercells, but choosing carefully the Brillouin zone sampling scheme, taking k -points that minimize the admixture between defect-related gap states and the host density of states. These methods are utilized in the calculation of the electronic structure of the vacancy, divacancy, and vacancy–donor pairs in Ge.

Ab initio study of neutral vacancies in InP using supercells and finite size scaling

The formation energies and relaxed structures of the neutral vacancies in InP are calculated by planewave density functional theory, using supercells of 8, 64, 216 and 512 atoms together with finite size scaling. The effects of electrostatic defect–defect interactions and the truncation of elastic relaxations by the finite supercell are examined. The unrelaxed formation energies are 4.95±0.10 and 3.00±0.10eV for VIn+0 and VP+0 respectively, and the relaxed formation energies are 4.20±0.05 and 2.35±0.15eV. When relaxed, VIn+0 remains very nearly symmetric with a 40% volume reduction, VP+0 on the other hand develops a double dimerized structure, with an ∼12% Jahn–Teller distortion and a 45% volume reduction. It is shown that finite size scaling sometimes reveals that energies are not converged even in the 512 atom supercell, and can thus be important tool in theoretical studies of defects in semiconductors, if sufficient care is taken with strongly Jahn–Teller active defects.

STM Nanospectroscopic Study of Defects in Semiconductors

AbstractCoupling of scanning tunneling microscopy (STM) with various schemes of optical spectroscopy was found to provide powerful tools for study of crystalline defects in bulk semiconducting solids. The simplest method was applied to a subsurface defect in a bulk GaAs crystal in which the signal was acquired by detecting the change in the tunneling current reflecting a local surface swelling that occurs when the wavelength of the chopped light used for spectroscopic measurements coincides with a photoabsorption spectral peak of the defect. Another scheme using a continuous light of variable wavelength was applied to midgap centers, assigned as arsenic antisite defects, densely populated in low-temperature-grown GaAs epifilms. Experiments at 90K revealed that light illumination causes reversible transformation of the individual defects to a metastable state with an excitation spectrum very close to one observed for the photo-quenching effect of EL2 centers in bulk GaAs.

Bulk Studies of Defects in Semiconductors

Bulk Studies of Defects in Semiconductors

Positron Beam Studies of Defects in Semiconductors

Positron Beam Studies of Defects in Semiconductors

Defect Studies in Semiconductors

Defect Studies in Semiconductors

Semiconductor Defect Studies Using Scanning Probes

Understanding how defects alter physical properties of materials has lead to improvements in materials growth as well as device performance. Transmission electron microscopy (TEM) provides an invaluable tool for structural characterization of defects. Our current knowledge of crystallographic defects, such as dislocations, would not have been possible without TEM. Recently, scanning tunneling microscopy and scanning force microscopy (SFM) have shown the capability of imaging surface defects with atomic or near-atomic resolution in topographic images. What is more important is to gain knowledge on how the presence of a certain type of defects changes the physical properties of materials. For example, how is the carrier lifetime altered near electrically active defects? How does photoresponse vary near grain boundaries? Where are defect levels in the forbidden bandgap? This talk will discuss several examples of how scanning probe microscopies (SPMs) can contribute to this aspect of defect studies in semiconductors.

Diffraction pattern of a defect: Two-dimensional angular correlation of positron-annihilation radiation studies of defects in semiconductors

Electron-positron momentum spectra of defects in semiconductors contain more information about the nature of the defects than has been recognized previously. Diffraction patterns that arise both from the nature of the electronic states and from the geometric structure can be seen in the simulated two-dimensional angular correlation of annihilation radiation spectra for positrons annihilating at a model vacancy in a tetrahedrally coordinated semiconductor. These should be experimentally observable in high-resolution spectra.

Structure of the intrinsic shallow electron center in AgCl studied by pulsed electron nuclear double resonance spectroscopy at 95 GHz.

In this Letter we report the first direct determination of the wave function of the intrinsic shallow electron center in silver chloride. A model is suggested in which an electron is shallowly trapped by two adjacent silver ions on a single cationic site. The information has been obtained by pulsed electron nuclear double resonance at 95 GHz and illustrates the potential of high-frequency EPR techniques for the study of defects in semiconductors.

Laplace transform deep-level transient spectroscopic studies of defects in semiconductors

A quantitative improvement in deep-level transient spectroscopy (DLTS) resolution has been demonstrated by using Laplace transform method for the emission rate analysis. Numerous tests performed on the software used for the calculations as well as on the experimental setup clearly demonstrated that in this way the resolution of the method can be increased by more than an order of magnitude. Considerable confidence in this approach was gained through measurements of a selection of well-characterized point defects in various semiconductors. The results for platinum in silicon and EL2 in GaAs are presented. For each of these cases conventional DLTS give broad featureless lines, while Laplace DLTS reveals a fine structure in the emission process producing the spectra.

Dynamics of defects in semiconductors

Hyperfine interaction techniques involving radioactive probe atoms like the perturbed γγ angular correlation technique (PAC) and the Mossbauer effect have, due to their inherent sensitivity, successfully been applied to the study of defects in semiconductors. By probing the characteristic charge distribution around the probe atom interacting with a defect, they contributed to the microscopic understanding of the nature, structure and stability of complexes formed between radioactive dopant atoms and defects present in elemental and compound semiconductors. Moreover, dynamic effects can be studied by hyperfine interaction probe techniques. In this case, dynamics always means the fluctuation of a charge distribution resulting in a time dependent hyperfine interaction within the time scale defined by the lifetime of the isomeric nuclear state used for the measurement. Such fluctuations can either be caused by structural changes like local rearrangements of a defect complex or by electronic transitions in the semiconductor resulting in a change of the charge state of a defect complex. Examples using PAC to monitor such processes will be discussed for the semiconductor silicon.

?-radiation detected nuclear magnetic resonance studies of point defects in semiconductors

An introduction to the principles of the β-NMR method is presented and its potential in the field of defect research in semiconductors is discussed. This is followed by a review of experimental applications to date and a description of several examples in some detail.

Sensitive electron paramagnetic resonance spectrometer for studying defects in semiconductors

The construction of a state-of-the-art electron paramagnetic resonance spectrometer for application to the studies of defects in semiconductors is described. The spectrometer is of superheterodyne type with low-frequency modulation of the magnetic field and working in dispersion. The use of a microwave synthesizer and a low-noise GaAs field-effect transistor amplifier results in ultrahigh sensitivity of the spectrometer which is experimentally shown to be 3×108 centers cm−3 with the test measurement being performed at 4.2 K for the easily saturable typical shallow donor center phosphorus in silicon. It is shown that this high sensitivity can be attributed to the use of the microwave synthesizer. The sensitivity of the spectrometer is improved by a factor 30 when a microwave synthesizer is used as microwave source instead of a quartz crystal stabilized klystron.

陽電子の科学と計測シリーズ ＶＩ．陽電子計測の応用 １．半導体の欠陥研究

陽電子の科学と計測シリーズ ＶＩ．陽電子計測の応用 １．半導体の欠陥研究

Combined Study of Complex Defects in Semiconductors

Combined Study of Complex Defects in Semiconductors