Joseph Blanc

Dislocation morphology in graded heterojunctions: GaAs1−xPx

The details of the formation, propagation, interaction, and densities of misfit dislocations are combined into a simple model quantitatively predicting dislocation densities for both abrupt and graded heterojunctions. Three key concepts are introduced: (1) misfit dislocations are segmented; (2) accordingly, they must give rise to a density of inclined dislocations, nI, that propagate through the growing layer; and (3) these inclined dislocations can bend in and out of any subsequently formed misfit plane to relieve the strain, and when bent in, serve as strain-relieving misfit dislocations. Thus, the value of nI is expected to remain constant with thickness. Also, nI is predicted to vary directly with the compositional gradient at the heterojunction. It is pointed out that there are two general classes of misfit dislocations, pure-edge and mixed and that their intersections, which cause the misfit dislocations to appear to bend within their plane, can be simply classified into three general types.Transmission electron microscopy was used for a comprehensive study of dislocations in a series of GaAs1−xPx heterojunctions prepared by a vapour phase growth technique. The main features of the above model were corroborated. The value of nI was found to be constant with growth distance as postulated, and in quantitative agreement with prediction, nI decreased from 4 × 107 cm−2 to 106 cm−2 as the compositional gradient decreased from 5% phosphorus/μm to 0.2% phosphorus/μm. Note that these values can far exceed the dislocation density of the substrates. Of particular significance, the inclined dislocations nI were found to propagate through a constant-composition region grown on top of a compositionally graded region, so that formation of the heterojunction must affect subsequently grown layers. Finally, it is shown that the misfit dislocations are, indeed, a combination of pure-edge and mixed, and all three postulated general interactions between these dislocations are shown to occur.

Like‐sign asymmetric dislocations in zinc‐blende structure

Symmetry considerations reveal that an asymmetry exists relative to orthogonal 60° dislocations of the same sign in zinc‐blende structure. The effect of this asymmetry has been observed in compositionally graded crystals of In1−xGaxP and GaAs1−xPx grown from vapor phase. It is observed that the spatial arrangement of the two sets of misfit dislocations in an orthogonal array is different. In one 〈110〉 direction, the misfit dislocations tend to be uniformly distributed, while in the other 〈110〉 direction there is a marked tendency for periodic banding of the dislocations.

Properties of High‐Resistivity Gallium Arsenide Compensated with Diffused Copper

Low‐resistivity n‐type GaAs crystals with silicon donors are compensated with diffused copper to produce high‐resistivity crystals in a manner which is amenable to semiquantitative description in terms of a simple thermodynamic model. The high‐resistivity GaAs:Cu crystals are subjected to photoelectronic analysis, including room temperature Hall and photo‐Hall measurements, to obtain information about the effects of deep‐lying imperfections on the properties of the initial n‐type GaAs. In addition to three deep donors previously reported, five acceptors are revealed. A 0.42‐ev acceptor level, when compensated, provides a long electron lifetime resulting in high n‐type photosensitivity at low temperatures. Evidence for effects on the electron mobility is obtained for compensated deep donor levels, important mainly in high‐resistivity n‐type material, and for compensated acceptors lying 0.22 ev above the valence band, important mainly at low temperatures.

Behavior of lattice defects in GaAs

Abstract Single crystalline samples of GaAs grown by either the horizontal Bridgman (HB) or floating zone (FZ) technique have been annealed in the range 450 to 800°C, usually for periods of 16 hr in either the presence or absence of copper. Measurements of thermally stimulated currents, dark conductivity, density, and thermal conductivity were carried out on samples at various stages of annealing. It was found that very large concentrations of traps (> 10 19 cm −3 ) can be introduced by annealing, and these are identified as lattice defects. It is proposed that there are two defects, a donor and an acceptor which occur both paired and isolated in the lattice. When paired, their ionization energies are roughly 0.2 eV, and when isolated are roughly 0.5 eV. There is a fundamental difference between FZ and HB crystals in annealing characteristics and of greatest significance, at 700°C in the absence of copper, the concentration of defects increases in FZ samples and decreases in HB samples. This indicates that the defects are not present in thermal equilibrium. Instead, the defects are probably introduced by an accident of growth during the growth process, in a neutral form such as a precipitate or antiphase domain. Copper acts as a catalyst in enhancing the rate of defect annealing.

A revised model for the oxidation of Si by oxygen

A conceptually simple modification of the Deal‐Grove model for oxidation of Si by dry oxygen provides an excellent fit to experimental data while removing the regime of ’’anomalously high’’ initial oxidation rates inferred by previous workers. The essential physical proposal is that while diffusion through the amorphous oxide is via molecular oxygen, Si oxidation occurs through the reaction of a small concentration of atomic oxygen.

The Si/SiO2 interface examined by cross‐sectional transmission electron microscopy

Thin (200–300 A) cross sections of Si/SiO2 have been examined by transmission electron microscopy at a resolution of better than 10 A to search for crystalline Si protrusions into, or islands in, the thermally grown SiO2. Within the resolution obtained, no evidence was found for any phase separation within the amorphous oxide layer.

Early growth of silicon on sapphire. I. Transmission electron microscopy

The early growth of Si on (0112) ‐oriented sapphire has been examined by transmission electron microscopy. The Si was deposited at 1000 °C by pyrolyzing silane in H2. The nominal growth rate was 0.4 μm/min. The morphology of the initial Si growth islands was determined after 0.5, 1.0, 2.5, and 3.5 sec of growth. The basic Si orientation is (100) with [011] Si∥[2110] Al2O3. Extensive faulting and twinning is observed leading to {221} orientations. These defects apparently form at coalescence sites of adjacent islands. Also present are four {110} orientations occuring as twin‐related pairs. The observation of isolated {110} domains indicates that they nucleate on the sapphire independently of the (100) domains. The {110} and (100) domains grow at about the same rate. Eventually, the {110} domains become trapped by the surrounding (100) domains. The volume percentage of the {110} domains is constant with growth time and equals 7% up to coverages of 90%.

The oxidation of silicon by dry oxygen can we distinguish between models

Abstract The purpose of this work is to examine why there is no consensus about the mechanisms controlling the oxidation of silicon by dry oxygen. It is shown that the time dependence of the oxide thickness is empirically never linear. It is argued that the parameters characterizing current models are known only within broad limits and that a wide range of physically distinct models have very similar mathematical forms. Two different physical models are scrutinized in detail, with the conclusion that they are in fact formally identical. Physical inconsistencies in such models are pointed out. Finally, some experiments which may ameliorate this situation are suggested.

Interdependence of strain, precipitation, and dislocation formation in epitaxial Se‐doped GaAs

The defect morphology of Se‐doped GaAs grown by CVD on undoped 100‐oriented GaAs substrates has been studied by transmission electron microscopy. Two types of samples are discussed: The first is nearly saturated, n ≅ NSe ≅ 4 × 1018 cm−3; the second is supersaturated, n ≅ 1.5 × 1019 cm−3, NSe ≅ 4 × 1019 cm−3. The nearly saturated samples exhibit an array of small features (probably Frank loops) near the original interface and have a density of misfit relieving dislocations ≲103 cm−1. The supersaturated samples show a large number of Frank loops, whose density decreases monotonically with distance away from the original interface while their diameter increases in this direction. The loops seem to be invariably connected with one or more very small precipitate particles of Ga2Se3. Most of the Frank loops are of the intrinsic type; these are sometimes accompanied by closely neighboring loops of extrinsic nature. Pure edge misfit relieving dislocations with a density ≅ 104 cm−1 are observed at the interface, r...

Photo-hall effects in photoconductors☆

Abstract Measurements of Hall mobility as a function of light excitation intensity at room temperature have shown a dependence of Hall mobility on intensity in single crystals of CdS, CdSe, GaAs, InP, and Si. Such a variation of Hall mobility under photoexcitation can result either from (1) a change in the microscopic mobility for single-carrier conductivity, or (2) the initiation of two-carrier conductivity. The recognition of the existence of these effects through photo-Hall measurements is essential for the interpretation of photoelectronic measurements, since simple measurements of conductivity or photoconductivity usually fail to reveal them. Results involving a change in microscopic mobility through photoexcitation indicate a change in scattering associated with the neutralization of charge in centers with an effective scattering cross-section of about 10 −10 cm 2 . A number of other effects resulting from the initiation of two-carrier conductivity have also been explored.