Etch pit density

Figure 2. The effect of dissolved Si concentration on etch pit density on quartz surfaces etched a) in sealed autoclaves for 6.5 hours, b) in a flow reactor for 6.5 hours (R5), 31.5 hours (R5SK), and 25-28 hours (R9). Reproduced with permission from Ref. 16. Copyright 1986 Pergamon Press.

Several refinements of our experiments could test these theories further. By measuring etch pit densities as well as pit dimensions on sequentially-etched crystals, nucleation rate data and pit growth data could be collected, yielding information about the rate-limiting steps and mechanisms of dissolution. In addition, since the critical concentration is extremely dependent on surface energy of the crystal-water interface (Equation 4), careful measurement of Ccrit yields a precise measurement of Y. Our data indicates an interfacial energy of 280 + 90 mjm- for Arkansas quartz at 300°C, which compares well with Parks value of 360 mJm for 25°C (10). Similar experiments on other minerals could provide essential surface energy data. 

An important aspect of any substrate that the reader should be familiar with is that it has a low defect concentration and good crystallinity. One measure of defects is the etch pit density or EPD, in which substrates are etched to highlight defects for counting. These defects subsequently often perpetuate themselves through the growing layer and become device failure loci. Crystallinity can be measured by X-ray diffracto-metry and is also a measure of material quality and hence defects. 

SLS thickness is thicker than the critical thickness [12]. It is suggested from the experimental results that the dislocations generated at SLS are bended by TCA2, resulting in the low dislocation density. Until now, the low etch pit density on the order of 10 cm has been obtained using SLS and TCA for the total epitaxial layer thickness of more than 3.5 pm [40-43]. Few papers have been reported on the growth of GaAs on Si, with the dislocation density of 10 cm at the epitaxial layer thickness of less than 3 pm. 

In the following, the quahty of epitaxial Si layers deposited either on an annealed porous Si layer or on a non-annealed porous Si layer is discussed. The epitaxial layer quality is evaluated by etch pit densities, defect densities, minority carrier lifetimes, or solar cell efficiencies. Table 1 gives an overview on the main characteristics of the epitaxial Si layers on the different types of porous silicon layers, i.e., single or double layers. 

The quality of epitaxially grown Si layer, using different deposition techniques and various types of porous silicon, was assessed by etch pit density, minority carrier lifetime, Hall mobility, microscopy, and device performance. 

For assessment of the dislocation density the etch pit density (epd) is measured according to DIN 50454-1 for LEC crystals and by a full-wafer mapping for VGF material using automated equipment. To reveal the emerging points of dislocations, the as-cut wafers are chemically polished in a H2S04-based solution to remove the damage and etched in a KOH melt at 400 °C. Typical examples of etched wafers are represented in Fig. 9.16. 

Y5 2.5 0.051 Capability of selective etching decreases. Reveals low etch-pit density. 

Larger etch pit densities of VCo.88 than of VCo,s3 form the subgrain boundaries characterized by the presence of substructure such as antiphase boundaries due to the formation of an ordered compound (150). The hardness of NbC decreases with carbon content and the hardness anisotropy of NbCo.8 is less pronounced than that of NbCo.9 (Fig. 11), which would be due to (a) deviation from stoichiometry of the crystal and (b) ordering of carbon vacancies. A high-resolution electron microscopy (HRFM) study gives very detailed information about defect order... 

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