The principal high resolution transmission electron microscopy techniques used in characterizing grain boundaries in electronic ceramics are described, including those recently developed for detecting the presence of extremely thin (∼10Å) intergranular phases. The capabilities of the techniques are illustrated with examples drawn from studies of ZnO varistors, PTC BaTiO3 devices and boundary layer capacitors.

Large size bicrystalline samples of NiO corresponding to tilt configurations around a < 110 > axis have been grown by the flame fusion technique, the misorientation angles varying from 0 to 180°. The variation of the relative energy of the grain boundary with misorientation has been studied and has indicated a very different behaviour from that previously observed by the authors on <100> tilt boundaries. High relative energy values and deep cusps on the energy curve at high coincidence angles are observed. The results are discussed in terms of interface energy.

The lattice imaging technique has been used to study grain boundaries in annealed, chemically vapor deposited (CVD) silicon. The majority of the grain boundaries are Σ*=3, 9 or 27, i.e. they are all twin related, and have boundary planes which coincide with high density planes of the appropriate coincidence site lattice (CSL). Asymmetric Σ=27 boundaries are found to be dissociated on an atomic scale into faceted Σ=3 boundaries and Σ=9 boundaries. No dissociation of the Σ=27 boundaries is observed when the boundary planes are symmetric.

The structure of the £=9 and £=11 tilt grain boundaries about [011] axis is studied by means of complementary electron microscopy techniques. Using α'fringes it is shown that the £=1l boundary translations amount to a large expansion and that the £ =9 is little dilated while the translation along [411] is not accessible. The diffraction technique yields the missing result : there is no translation along [411] : the boundary periodicity is not in both cases that of the coincidence site lattice. A supplementary symmetry occurs in the £ =9 boundary which leads to a shortest periodicity. The observations are consistent with the model of five- and seven-fold rings describing the £ =9 boundary. A model, without dangling bond, which consists in a combination of the £ =9 and £ =3 (coherent twin) patterns, is proposed for the £ =ll boundary.

Dislocations in low-angle tilt boundaries exhibit a wide variety of Burgers vector including a/2<112> a<001> and a<111>. The dislocations are usually dissociated: Shohkley, stair-rod and Frank partial dislocations may each be formed together with associated intrinsic and extrinsic stackingfaults. Dislocations in low-angle {111} twist boundaries are usually assumed to dissociated by a glide mechanism to give two types of extended nodes, known as P–type and K–type, which contain intrinsic and extrinsic stacking-faults respectively. It is shown that dissociation by climb actually occurs for both types of grain boundary.

Grain boundaries exert a profound influence on the electrical behavior of semiconductors. First order twin boundaries are the simplest and most common interfaces which occur in polysilicon. We have studied the dislocation structure and preferred boundary plane orientation of such twins by transmission electron microscopy. In addition, we have investigated the atomic structure of twin boundaries on {111} and {112} planes using an interference technique which permits the relative position of two lattices to be determined with a precision of about 0.05Å. Knowing the relative orientation and position of two crystals, together with the interface plane, permits the atomic configuration at the interface to be inferred. We find that the interface structure is surprisingly complex and that more than one atomic configuration is possible for a given grain orientation and interface plane. It is therefore not unexpected that even twin boundaries can show variations in electrical properties.

The behaviour of Fresnel fringes with focus has been investigated as a means of characterising grain boundaries in engineering ceramics. This technique, together with dark-field imaging, has been applied to the study of grain boundaries in two hot-pressed silicon carbides. It is demonstrated that these two techniques, applied together, provide the best means of obtaining a complete characterisation of grain boundary films, in terms of width, structure, and composition.

Although coherent twin boundaries in silicon are electrically inactive, dislocations in the boundaries can act as efficient recombination centers for minority carriers. Different twin boundary dislocation arrangements have been studied by EBIC and TEM. It is found that the observed EBIC contrast is dependent not only on the arrangement of the dislocations in the boundaries but also on the inclination of the boundaries to the surface. It is shown that different defect configurations can produce similar EBIC contrast.

The interaction potentials between solutes and grain boundaries in ionic solids are identified as [1] the electrostatic interaction between the charged solutes and grain boundaries and [2] the elastic energy due to size misfit of solutes in the matrix. Equilibrium solute distribution is calculated from the defect distributions leading to the minimum free energy. Space charge distributions near interfaces during kinetic processes are evaluated. We analyze the limiting case of constrained equilibrium in which the vacancy distribution and degree of solute-vacancy association satisfy a minimum free energy under the constraint of no solute redistribution.

We have studied the influence of doping and oxidation on grain growth of small grain polysilicon. Intrinsic and phosphorus doped (to 1021 /cc pseudo-amorphous layers of Si were prepared by chemical vapor decomposition of SiH4 at 600°C on thermally grown SiO2 on Si wafers. These samples were then annealed in N2 or O2 ambients at 1000°C for 30 minutes. Transmission electron microscopy examination of the samples revealed that grain boundary dislocations were commonly present at high angle boundaries and that there was a remarkable disparity in mean grain size, d, for the different samples. It was found that d was greater for (a) doped poly than intrinsic poly annealed in either N2 or O2, and (b) for the same polysilicon starting materials (doped or undoped) annealed in O2 than in N2. We propose that these phenomena may be explained by the influences of dopant and point defects on grain boundary dislocation mobility which in turn governs grain boundary migration. An atomistic model of grain boundary migration has been developed. A key aspect of the model is the formation and motion of jogs and kinks on grain boundary dislocations. These processes are directly influenced by the behavior of point defects in the material and its electronic properties.

A CAMECA IMS-3F secondary ion microscope has been used to investigate the presence of impurities in cast polycrystalline silicon wafers and to determine their lateral distribution. Cesium and oxygen ion bombardment were used to selectively detect potential impurities and extract their lateral distribution with submicron lateral resolution.Images of H, C, O, P, and Cu segregated in grain boundaries have been obtained from polycrystalline silicon.

This paper describes a novel technique that utilizes vapor-phase epitaxy to grow bicrystal semiconductor layers with predetermined rotation axis, misorientation angle, and grain boundary plane. The geometrical structure of the grain boundary in each layer is therefore completely specified. The technique has been demonstrated by using the AsCl3-GaAs-H2 method to grow a series of GaAs bicrystals, each containing a [110] tilt boundary formed by a grain with a (111)B boundary plane and a grain rotated from (111)B by a selected misorientation angle. The results of initial electrical measurements indicate that the height of the potential barrier associated with each grain boundary varies with the misorientation angle.

Grain boundaries play an important role in determining the operating characteristics of devices such as varistors and thin film solar cells and transistors. In the last several years detailed one-electron expressions have been developed for the transport coefficients of majority and minority carriers at grain boundaries. These theories have been successful in predicting the measured electrical properties of bicrystals in lightly doped silicon. The status of our understanding in this area will be reviewed in some detail. Recent extensions of these calculations which have been necessary to explain measurements on grain boundaries in degenerately doped GaAs will also be reviewed.

By comparison of the capacitance and the conductivity of p–type Si bicrystals, we show quantitatively that current transport occurs through thermionic emission of holes across the potential barrier, which is caused by charged donors in the grain boundary. Starting from this finding, we propose a simple model which allows for the first time a spectroscopic determination of the grain boundary density of states from photocapacitance data. Results indicate the presence of band tails and additional mid-gap states.

We have studied the photoconductivity of grain boundaries in p–type silicon. The result demonstrates the applicability of the technique for the measurement of minority carrier recombination velocity at the grain boundary. The experimental data are consistent with the thought that the recombination velocity increases with the boundary state density and light intensity.

A special type of high angle grain boundary with mirror symmetry of the crystallographic orientation between the two grains is examined electrically and structurally. Transmission electron microscopy investigations show the nonuniform nature of the grain boundary. Both coherent and incoherent regions are observed along the boundary plane, and the types of dislocations and their densities vary from place to place. Electrical measurements of the boundary properties indicate no measurable barrier height. Heat treatment of the sample in an oxygen atmosphere at 950°C for 30 min did not change the boundary resistance. However, recombination effects are enhanced after boron diffusion. When pulsed laser radiation was used to process this material, it was found that the grain boundary structures were modified by laser-induced surface melting, i.e., incoherent boundaries were converted to coherent boundaries in the melted region.

Steady state and transient capacitance (DLTS) measurements have been performed on a low angle tilt boundary in a germanium bicrystal, in combination with an electron microscope study of the boundary dislocation structure. A characteristic level has been found at 0.42 eV below the bottom of the conduction band, with a density about 109 cm-2 and an electronic capture cross-section about 5 × 10-12 cm2.

Examination of capacitance transients arising from the emission or capture of electrons at a charged GaAs grain boundary reveal for the first time the existence of discrete interface levels. The position of these levels in the bandgap and their associated capture cross sections are determined from the transients.

The density of states at the grain boundary is found to be a complicated function of both the defect state property and the physical location of the defect at the boundary. A modified double-depletion-layer model concerning the nonuniform distribution of defects along the boundary is presented. A method is developed which can estimate the level location from the complex DLTS spectra.

After treatment in a deuterium plasma, the D.L.T.S. spectrum associated with grain boundaries in p–type Si is found to reduce to a narrow band centered at 0.32 ± 0.02 eV with a total density of 5 ⨉ 1015 cm−2 . However, the capture cross-section, measured to be ∼ 2 × 10−20 cm2 , is 10 times larger than the apparent cross-section associated with the states present in unpassivated material.