Etch Hillocks Research Articles

Single crystal Cu 2S/CdS photovoltaic devices with optimum performance before a post barrier air bake

The separate stages in the preparation of Cu 2S/CdS photovoltaic devices on single crystal substrates have been investigated carefully using the techniques of reflecttion electron diffraction and scanning electron microscopy. Mechanical polishing of hexagonal single crystal CdS produces a polycrystalline surface layer with cubic structure which, for efficient cells, has to be removed by chemical etching before the topotaxial Cu 2S layer is formed. Different types of etched surfaces have been produced and found to be closely related to the polishing procedure. The nature of the etched surface has a strong influence on the cell characteristics. Devices made on surfaces with many ledges and kink sites on the sides of the etch hillocks have poor diode characteristics and photovoltaic behaviour in the as-made condition, whereas cells formed on surfaces with faceted hillocks have good rectifying and photovoltaic properties at this stage. While a post barrier air-bake is essential to improve cells which have poor characteristics in the as-prepared condition, it has a deleterious effect on devices with good characteristics in the as-made state. The highest efficiencies are obtained with as-plated cells fabricated on surfaces etched to produce hillocks with well developed facets on substrates with optimum resistivity.

Motions of Individual Dislocations in White Tin Single Crystals Deformed in Tension

The motions of individual dislocations and dislocation arrangements in white tin single crystals deformed in tension were closely investigated using the etch hillock technique. When dislocations of the slip system (010) [100] move, they form bands (A-bands) which contain a high density of dislocations and run nearly perpendicular to the direction of motion of the dislocations. Such bands are formed from two groups of dislocations which approach each other from opposite sides. The motions of dislocations during and after unloading were also investigated. The A-band has some dislocation-vacant areas which are frequently surrounded by dislocation arrays aligned in a direction inclined by about 45° to the direction of motion of the dislocations.

Distribution of Obstacle Spacings to Dislocation Motion in the Pre-Yield Region in White Tin Single Crystals

Moved distances of individual dislocations were measured on the surface of a single crystal of white tin by using the etch hillock technique. In this technique, the moved distance was just coincident with the length of a hillock trace l. The applied stress was lower than that at the elastic limit. That is, the stress was maintained below 50 g/mm2. The distribution of the moved distance of dislocations was obtained by measuring the length of the individual hillock traces. The result was theoretically analyzed on the condition that the obstacles were randomly distributed and the deduced distribution function ϕ(l) showed good agreement with the experimental results. As a result, the obstacle for the moving dislocation in the range of the stress lower than that at the elastic limit was found to be mainly constructed by stationary dislocations.

Detection of Structural Defects in N‐type InP Crystals by Electrochemical Etching under Illumination

An experimental study has been made of the detection of structural defects in n‐type crystals by electrochemical etching under illumination. Under illumination, presence of structural defects such as mechanical damage or grown‐in defects on the crystal surface led to a decrease of dissolution rate of the surface. This enabled structural defects to be revealed as etch hillocks. Surface damage introduced during handling processes of the crystal was detected with high sensitivity. By observing etch hillocks, detailed information was obtained regarding fine structure and distribution of dislocations or dislocation clusters in nominally undoped crystals. It was found that novel defects, which were not involved in nominally undoped crystals , were involved in highly sulfur‐doped crystals with low dislocation densities .

Image Forces Acting on Dislocations with the Burgers Vector ½ in White Tin Single Crystals

Edge dislocation walls with many steps are revealed on the (001) surface of deformed, and then annealed, crystals by an etch hillock technique. It is found that dislocations at the steps have the Burgers victor ½<111>, which is different from that of wall dislocations. Configurations of these dislocations are observed, and classified into two types when a single dislocation exits at a step and into four types when two dislocations exist there. These unusual equilibrium configurations are interpreted by taking image forces into account.

The Dislocation Movement in the Pre-Yield Region in White Tin Single Crystals by Using the Etch Hillock Technique

Single crystal plates of white tin were stretched in an etching solution to designated stresses below the macro yield stress using an Instron type tensile machine. The etching solution produced hillocks at the sites of dislocations and trails of hillocks along the loci of moved dislocations. Two types of dislocation movements could be distinguished by the shapes of hillock trails. The one corresponds to the movement of a dislocation which terminates at the surface, and the other, the movement of a dislocation which emerges by stressing from the interior. The movement of the former type takes place at stress levels ranging from about 30 g/mm2 to 50 g/mm2. The movement of the latter type occurs more frequently as the stress increases. The distribution of the trail length was found to depend on the dislocation density.

Dislocation Walls Consisting of Double Arrays in White Tin Single Crystals

Dislocation walls consisting of double arrays were revealed on the (001) surface of deformed, and then annealed, crystals by an etch hillock technique. It was found that dislocations in the wall have the Burgers vector ½<111>, and that the wall was split into two arrays at the surface but had nearly merged into a single array below the surface. This particular configuration may be well interpreted by assuming that the wall is composed of two kinds of dislocations with Burgers vector having a common edge component but alternate screw component, and by taking the image force of each dislocation into consideration. The analysis indicates that the depth over which the split of the wall extends is approximately equal to the spacing between dislocations in the wall.

Configurations, Formation and Burgers Vector of Coupled Dislocations Straddling a Polygon Wall in White Tin Single Crystals

A variety of configurations of coupled dislocations straddling a polygon wall were revealed by the etch hillock technique on the (001) surface of white tin. Observations indicated that: (1) Both coupled dislocations and wall dislocations move to the same [100] direction under an applied stress; (2) Their slip plane is (010); (3) The orientation of the plane of the wall is (100); (4) The simple configurations of coupled dislocations may be formed by the combination of two walls and the subsequent rearrangement during the annealing procedure. The equilibrium positions of coupled dilocations were measured in each of ten configurations and analyzed on the basis of anisotropic elasticity. A good agreement between the observed and calculated values for all the configurations was obtained within a few per cent only when the slip system of the dislocations was assumed to be (010) [100]. This assumption was also consistent with all observations in this work. From these results, it was deduced that the slip system (010) [100] is operative in this material in addition to seven slip systems reported hitherto.

Selective delineation of dislocation in the K2O-SrO-Nb2O5 system

A comprehensive study of dislocations in the K2O-SrO-Nb2O5 system has been carried out and the etchants (i) HF (48%) and (ii) a mixture of H2SO4 (95%), HNO3 (70%) and HF (48%) in the ratio 5:2:2 by volume were found effective in revealing dislocations on (001) cleavages of this system. Two types of pits, deep and shallow, and well-defined pyramidal etch hillocks were observed on the same surface on etching with HF. A comparative study of the etch patterns of the two etchants has also been made. The results are analysed and their implications are discussed.

Etching of MgO crystals in acids: surface micromorphology

Several etchants based on simple acids are proposed for revealing dislocations on {100}, {110} and {111} faces of MgO single crystals. Some acids under different etching conditions are shown to produce etch pyramids at decorated dislocations, while etch hillocks, spherulites and dendrites are formed under different conditions. With increasing concentration of H2SO4, 〈110〉 pits, circular pits, 〈100〉 pits, 〈110〉 pyramids as well as 〈100〉 pits, dendrites and spherulites, and hillocks are formed in that order. Etching characteristics of other acids also showed a more or less identical trend. The observations are interpreted with the assumption that with increasing concentration of acid, an effective undersaturation and later supersaturation is developed very close to the dissolving crystal face. The chemistry of the dissolution process is also discussed.

Sources of oxidation-induced stacking faults in Czochralski silicon wafers

Using optical microscopy/etch pit techniques for the delineation of defects in {100} Czochralski silicon wafers we have made a one-to-one correlation between bulk stacking faults in oxidized wafers and etch hillocks identified at the same sites before oxidation. Transmission electron microscopy of the hillock defects shows them to be clusters of precipitates ranging in size from 0.01 to 0.3 μm. A discussion of these stacking-fault nucleation sites in light of previous work on ’’swirl’’ defects in float-zone wafers and attempts at preoxidation gettering are also presented along with a model for the formation of the extrinsic stacking faults.

Chemical etching of (1 0 0) GaAs in the HNO3-HF-H2O system

This paper describes the action of solutions containing nitric acid, hydrofluoric acid and water on GaAs of (1 0 0) orientation. Single-crystal slices of the semiconductor were immersed in the etch and the rate of dissolution was measured. Results were taken over a wide range of composition of the solution. The results show a marked resemblance to the etch-rate data for silicon in the same etching solution, although the actual etching rates for GaAs were lower. The semiconductor surfaces were observed carefully after etching, using techniques of optical microscopy and scanning electron microscopy. Etch hillocks were observed for many compositions of the etch. It was found that the hillocks were covered by a layer of oxide: if any of this oxide covering came off, the hillock quickly disappeared. Sequential etching experiments showed that the hillocks were not associated with dislocations. Both the etch-rate data and the microscopic examination of the GaAs surfaces suggest that the system is probably diffusion-limited over the range of etch composition studied in this work.

Oxidation stacking faults in epitaxial silicon crystals

Oxidation stacking faults (SFs) in epitaxial silicon crystals have been studied by means of preferential etch and X-ray topography. SFs lie on {111} planes and are surrounded by a partial Frank dislocation. Nucleation takes place at crystallographic defects located near the surface of epitaxial layers. These defects appear as etch hillocks after preferential etch. SF length as a function of temperature and time for different thermal treatments is reported. The SF length is controlled by an activation energy of 2.6 eV. This energy, which is nearly half the self diffusion activation energy of silicon, supports a SF growth mechanism controlled by vacancy emission.

Etching study of microdomains in LiNbO3 single crystals

Microdomains in LiNbO3 single crystals have been investigated in considerable detail by the etch technique. Etch features, such as etch hillocks on the negative c surface, etch pits on the positive c surface, and needle−shaped etch patterns on the Y surface, have been examined by optical and electron microscopy. The results of detailed observations of the features lead to the conclusion that a common source of these patterns is a reverse polarized needlelike microdomain, less than 1 μm in diameter and 300 μm in length, lying parallel to the c axis, namely the polarization axis of LiNbO3. Mechanical scratching on the c surface and the subsequent chemical etching produce new hillocks on the negative surface and etch pits on the positive surface. It has been proposed that the polarization reversal takes place on a microscopic scale by scratch−induced stress.

Formation of etch hillocks in white tin

Pyramidal shaped hillocks were formed by etching on the {001} surface of white tin at the sites of dislocations. To make the phenomenon of hillock formation clear, two sorts of etchants were used; one (B) contained a small amount of Cu ions and the other (A) did not. Hillocks were formed where small particles of inhibiter for dissolution existed. That is, particles were always observed at the centers of pyramidal hillocks. These particles were either Cu, precipitated from the B-solution, or impurity atoms segregated along dislocation lines (A-solution). The temperature dependence of the density of Cu ions in the etchant favorable to hillock formation only at the sites of dislocations was obtained experimentally. It is estimated that 2 E. 1− E 2− E 3 = 0.36 eV, where E 1 and E 2 are activation energies of a Cu ion on the crystal surface to get into the etchant and to the neighbouring potential minimum on the same surface, and E 3 is that of a Cu ion in the etchant to get onto Sn surface, respectively.

Etch hillocks in LiNbO3

Abstract The origin of etch hillocks on the negative C-surface of LiNbO3 crystals has been investigated by means of optical and electron microscopy. From detailed observation on the hillocks, it has been concluded that the source of the hillocks is a reverse polarized needle-like microdomain lying parallel to the C-axis.

Chemical etching of {1 1 1} and {1 0 0} surfaces of InP

The effects of a number of chemical etches on the III–V semiconductor InP were studied, using {1 0 0} and {1 1 1}-type faces. The (1 1 1) and (¯1¯1¯1) faces were found to behave differently, and this was attributed to the polarity of the zinc-blende lattice. Curves showing etching rate as a function of penetration were plotted, and it is noted that they demonstrate an enhanced etching rate close to the surface. This is attributed to the damaged surface layer associated with the cutting of a crystal slice. Photographs were taken at various stages of the etching using both the optical and scanning electron microscopes. Both etch pits and etch hillocks were observed. The shapes of the pits are compared to those described in previously published work, and possible reasons for these shapes are discussed. The conditions necessary for the production of an etch hillock are described and it is shown that the measured etching rates are consistent with hillock formation in the case of the 1 HCl∶1HNO3 etch. The mechanisms of dissolution are discussed and it is suggested that both activation control of the dissolution process and diffusion control were observed in the work.

Dislocation Etch Hillock Formation in White Tin Single Crystals

The mechanism for producing pyramidal etch hillocks at the sites of dislocation on the {001} surface of white tin is studied. The hillock formation results from the etch resistant materials existing at the dislocation sites on the crystal surface. These materials come from (1) the segregation of impurities contained in the crystal itself along the dislocation lines, and (2) the precipitation of copper or silver atoms contained in the etching solution at the clean dislocation sites. The role of impurities to produce hillocks is demonstrated and the mechanism for the development of hillocks is derived from the nature of dissolution of the {101} surface enclosing hillocks. Application of this mechanism to another crystal is suggested.

X-ray study of small dislocation loops in thermally oxidized silicon

Lattice defects in thermally oxidized silicon waters have been investigated by X-ray transmission topography. Many dotted lattice defect images were observed in the X-ray topographs. From observation of the variation in the image contrast between reflecting planes, it was found that these defects have a principal displacement along one of the 〈111〉 directions and another small displacement component perpendicular to this direction. The surfaces of the specimens were chemically etched in Sirtl solution after X-ray topography. Etch hillocks were found to be loops and half loops in the optical micrographs. One-to-one correspondence was found to exist between the etch hillocks and the X-ray images of defects. It was concluded that the defects are small dislocation loops and half loops lying on one of {111} planes and having a Burgers vector a/3 〈111〉 normal to the plane. The shapes and the contrasts of Observed X-ray images were well explained by the displacement around a partial dislocation of edge type.

Etch hillocks on carbon faces of α SiC

Etch hillocks are observed on the carbon faces (B faces) of silicon carbide when they are etched in a mixture of NaOH + KNO3 (2: 1 by weight) at 630°C. The nucleation and development of hillocks, their origins and formation are studied in detail. A definite correlation between these hillocks and the sites of dislocations has been established. The studies reveal that an inhibitive action at the sites of dislocations and an enhanced general dissolution around the immediate vicinity of these centres are the reasons for this behaviour. Further, some sort of deposition, possibly SiC itself, at these sites is also suspected.