Twin generation in zinc-blende type III–V compound semiconductors: New insights from an InP case study
The type of twinning in zincblende-or sphalerite-type III-V compound semiconductors is well known. However, its detailed formation mechanism, although intensively studied in the eighties and nineties, is not entirely understood. In addition to a lot of empirical observations, there is a theoretical approach, published in 1995 [1] and improved in 1998 [2]. The latter predicts a correlation between crystal slope angle a and twin generation frequency. However, a critical overview of our own experimental results on GaAs and InP, grown by LEC (Liquid Encapsulated Czochralski) and VCz (Vapour Pressure controlled Czochralski) techniques, leads to no unambiguous relation between twin formation and crystal slope angle. This paper gives a comparison between experimental results and the above mentioned theory, revealing that twinning is more correlated to dynamical effects like oscillations of growth rate, i.e. noise of the system.
Interface and facet control during Czochralski growth of (111) InSb crystals for cost reduction and yield improvement of IR focal plane array substrates
Focal plane arrays (FPAs) made on InSb wafers are the key cost-driving component in IR imaging systems. The electronic and crystallographic properties of the wafer directly determine the imaging device performance. The “facet effect” describes the non-uniform electronic properties of crystals resulting from anisotropic dopant segregation during bulk growth. When the segregation coefficient of dopant impurities changes notably across the melt/solid interface of a growing crystal the result is non-uniform electronic properties across wafers made from these crystals. The effect is more pronounced in InSb crystals grown on the (111) axis compared with other orientations and crystal systems. FPA devices made on these wafers suffer costly yield hits due to inconsistent device response and performance. Historically, InSb crystal growers have grown approximately 9-19 degree off-axis from the (111) to avoid the facet effect and produced wafers with improved uniformity of electronic properties. It has been shown by researchers in the 1960s that control of the facet effect can produce uniform small diameter crystals. In this paper, we share results employing a process that controls the facet effect when growing large diameter crystals from which 4, 5, and 6” wafers can be manufactured. The process change resulted in an increase in wafers yielded per crystal by several times, all with high crystal quality and uniform electronic properties. Since the crystals are grown on the (111) axis, manufacturing (111) oriented wafers is straightforward with standard semiconductor equipment and processes common to the high-volume silicon wafer industry. These benefits result in significant manufacturing cost savings and increased value to our customers.
A new technique for decalcifying thin ground specimens of adult human enamel.
Abstract A new decalcification technique is described for the recovery of the organic matrix from thin ground specimens of adult human enamel. An aqueous solution of chromium sulphate which has both fixing and decalcifying properties is used. The results are compared with those obtained when an adjacent part of the same ground specimen was decalcified with the hydrochloric acid solution of Brain (1962). Dependent on slight differences in pH of the chromium solutions, two different appearances of the recovered matrix are obtained: above pH $ 3.2 a structural matrix which is positively birefringent at refractive index 1.55, whereas below this pH a matrix which is homogeneous and non-birefringent and almost similar to the matrix obtained after hydrochloric acid decalcification. The two types of matrices are discussed and the one favoured on morphological grounds, the chromium sulphate structural matrix, is related to present concepts of the structure of the native enamel matrix.