Structure Of Defects In Semiconductors Research Articles

Computational and experimental identification of hydrogen defect vibrational modes in zinc sulfide

The characteristic extrinsic infrared absorption in bulk chemical vapor deposited (CVD) ZnS has been unambiguously identified. High resolution absorption measurements and ab initio vibrational calculations identify the absorption of 1760–1580 cm−1 as due to defects of the form (ZnHn)S, with n = 3 being the highest concentration. Multiple absorption peaks in this spectral region are due to Zn-H stretching from different bond lengths. Phonon spectra calculations of hexagonal ZnO impurities do not account for the spectral position of the absorption without three-phonon processes and thus are unlikely to be responsible for the extrinsic infrared absorption in CVD ZnS. This work shows the complementary utility of computational and experimental work for identifying defect structures in semiconductors.

The formation of the periodic defect structures in semiconductors under the influence of an acoustic wave

The formation of the periodic defect structures in semiconductors under the influence of an acoustic wave

Imaging and spectroscopy of defects in semiconductors using aberration-corrected STEM

The distribution of single dopant or impurity atoms can dramatically alter the properties of semiconductor materials. The sensitivity to detect and localize such single atoms has been greatly improved by the development of aberration correctors for scanning transmission electron microscopes. Today, electron probes with diameters well below 1 A are available thanks to the improved electron optics. Simultaneous acquisition of image signals and electron energy-loss spectroscopy data provides means of characterization of defect structures in semiconductors with unprecedented detail. In addition to an improvement of the lateral spatial resolution, depth sensitivity is greatly enhanced because of the availability of larger probe forming angles. We report the characterization of an alternate gate dielectric interface structure. Isolated Hf atoms are directly imaged within a SiO2 thin film formed between an HfO2 layer and the silicon substrate. Electron energy-loss spectroscopy shows significant changes of the silicon valence state across the interface structure.

Comparison of the Koster-Slater and the equation-of-motion method for calculation of the electronic structure of defects in compound semiconductors.

Traditional methods of calculating the electronic structure of defects in semiconductors rely on matrix-diagonalization methods which use the unperturbed crystalline wave functions as a basis. Equation-of-motion (EOM) methods, on the other hand, give excellent results with strong disorder and many defects and make no use of the basis of unperturbed wave functions, but require self-averaging properties of the wave functions which appear superficially to make them unsuitable for study of local properties. We show here that EOM methods are better than traditional methods for calculating the electronic structure of essentially any finite-range impurity potential. The reason is basically that the numerical cost of the traditional Green's-function methods grows approximately as ${\mathit{R}}^{7}$ o/Iper sitet/P, where R is the range of the potential, whereas the cost of the EOM methods per site is independent of the range of the potential. Our detailed calculations on a model of an oxygen vacancy in rutile ${\mathrm{TiO}}_{2}$ show that a crossover occurs very soon, so that equation-of-motion methods are better than the traditional ones in the case of potentials of realistic range.

Delayed optical detection of magnetic resonance for defects in Si and GaAs

We report on a modified optically detected magnetic resonance (ODMR) technique, here called delayed ODMR (D-ODMR), for studies of geometric (atomic) and electronic structure of defects in semiconductors. This D-ODMR technique is shown to be very successful in overcoming the dominating optically detected cyclotron resonance background signal in ODMR studies of defects in Si and GaAs.

High resolution energy-loss spectroscopy

In principle, Electron Energy-Loss Spectroscopy in the Scanning Transmission Electron Microscope can obtain information related to the electronic structure of single defect structures in semiconductors. The instrumental requirements necessary to accomplish this are discussed. Examples include: Si and GaAs interband excitations, graphite EXELFS analysis, and surface and defect induced structure at the SiL 2,3 edge.

Valence-bond theory of off-center impurities in silicon: Substitutional nitrogen.

A theoretical description of the electronic structure of defects in semiconductors is presented that emphasizes the local bonding environment of the defect. For quantitative results, correlated ab initio wave functions, within the generalized valence-bond method (GVB), are used in describing defect properties. Explicit, detailed calculations are presented for the example of the substitutional nitrogen defect in silicon. The language of bond pairs, lone pairs, and dangling bonds---concepts well defined within the context of the GVB wave functions used here---is found to be a natural language for the discussion of simple defect behavior. The heretofore obscure driving force for the observed ${C}_{3v}$ ground-state geometry for Si:${\mathrm{N}}_{\mathrm{Si}}$ is revealed to derive from local bonding considerations: The nitrogen atom prefers to form only three covalent bonds and have one lone pair, as in ammonia; this naturally results in a ${C}_{3v}$ ground state. Calculations confirm this description, but the arguments are not dependent on them. The crucial role of electronic correlation, neglected in mean-field approaches, for the description of the character of the local electronic structure of a defect is detailed. Comparisons are made between the results of correlated GVB and mean-field Hartree-Fock calculations which illustrate the importance of electronic correlation effects. The wave functions obtained are then used to calculate the hyperfine coupling parameters, from valence Mulliken analyses and directly from all-electron calculations. Agreement with the very detailed results of electron paramagnetic resonance experiments is quite good and the values obtained are insensitive to minor alterations to the model. The arguments used for the nitrogen-impurity case are not species specific; the behavior of a large class of defects can be qualitatively described by the judicious application of well-established local chemical and physical concepts. A few representative systems are discussed qualitatively to illustrate the usefulness of the simple concepts presented here.

Characterization of defects in semiconductors by combined application of SEM(EBIC) and SDLTS*

SUMMARYBesides the characterization of the geometrical structure of defects in semiconductors by TEM the estimation of their electrical activity is of importance. SEM(EBIC) and SDLTS (scanning deep level transient spectroscopy) are especially suitable for this purpose; they allow the inspection of electronic properties with a spatial resolution in the micron‐range. On the one hand, SEM(EBIC) yields information on the recombination efficiency of defects in the crystal volume adjacent to a pn junction or a Schottky barrier; on the other hand, SDLTS enables the detection to be carried out of the distribution and the energetic levels of deep level defects lying in the space charge region. Accordingly, the combined application of these techniques is very promising for investigating physical processes implying an inhomogeneous incorporation of deep level defects in semiconductor crystals.In comparison to the widely used SEM(EBIC) technique SDLTS has only rarely been applied, a fact that is due to the high detection sensitivity necessary for measuring capacity transients. The application of a highly sensitive (10—6 pF) micro‐computer‐controlled SDLTS system in combination with a conventional EBIC system allows a reliable inspection of semiconductor materials and devices, based on A3B5 compounds and on silicon. A typical application of the above technique is the investigation of the impurity distribution around extended crystal defects, like dislocations and precipitates, to study their gettering activity.

A cathodoluminescence detection system for TEM/STEM

The ability to correlate near-atomic resolution TEM images of defects with their cathodoluminescence (CL) spectra holds promise as a powerful technique for the study of the electronic structure of defects in semiconductors. We have constructed a CL detection instrument fitted to a Philips 400T electron microscope, similar to that described by Roberts, as shown in Fig. 1. The instrument uses an ellipsoidal mirror for light collection allowing operation in the TEM, STEM and REM modes in a relatively clean vacuum, and is compatible with the ELS and EDS modes. The ellipsoidal mirror was designed to collect the maximum amount of emitted light within the limitations of the spacing between the specimen holder and the upper pole piece of the twin lens, as shown in Fig. 2 and 3. The length of the major axis is 61.2 mm and that of the minor axis is 12.1 mm.