Defects in Silicon Crystals Grown by the VLS Technique

Abstract

Crystalline defects have been studied in silicon crystals grown by the vapor-liquid-solid (VLS) technique. Most of these crystals are highly perfect. However, some crystals contain defects such as dislocations, stacking faults, and second-phase regions. An elastic stress field, resulting from differential thermal contraction was found near the tip of every crystal. The formation and prevention of these defects and their relation to the VLS growth mechanism are discussed in detail. The morphology of the prismatic side faces of the crystals depends on deposition temperature, and is primarily due to vapor-solid deposit. This deposit is perfect even at deposition temperatures as low as 700°C.

Enhanced absorption and carrier collection in Si wire arrays for photovoltaic applications

“…Because each wire array was subject to identical etching conditions during processing, we suspect that this absorption may be due to entrapped particles of catalyst metal, rather than surfacestate or bulk-trap assisted absorption as previously suggested. Catalyst metal inclusions have been observed in Au-catalyzed VLS-grown Si wires, 15 and it is known that Cu and Ni readily precipitate upon rapid cooling within crystalline Si. 16 Unfortunately, the cooling rate of wires following VLS growth varied greatly (and was not controlled) in this study.…”

Radial PN junction, wire array solar cells

“…%muhol= [500,500,500,400,300,150,60,50,50]; %these lines indicate the maximum electron and hole mobilities possible in Si at various doping levels, as…”

“…The current density can then be calculated by integrating the carrier density gradient in the z-direction over the plane of the pn junction, for both carrier types. For example, the current density due to electrons in the p-type quasineutral region, J p , is given by 60) where 61) and R and L are the radius and length of the wire, respectively. Shown in Fig.…”

“…[32] [33] This has many desirable features for our purposes: wires formed by this technique tend to grow as single crystals; [60] under the right conditions, VLS-grown wires can inherit their growth orientation from the growth substrate; [61] VLS has been shown to be capable of high growth rates (up to several μm/s); [62] in the VLS approach, growth occurs from gas phase precursors, which in the case of Si can be of very high purity and/or inexpensive relative to alternative sources of Si, as well as allowing in principle for in-situ doping; [63] and the wide range of wire dimensions, and the high degree of control of wire diameter and position, that are possible with this technique. [64] [65] In this technique, as it applies to Si growth, an impurity metal is used to form a liquid alloy droplet with Si, of relatively low freezing temperature, when Si is introduced from the gas phase via a Si-containing molecule such as SiH 4 or SiCl 4 .…”

Growth, Thermodynamics, and Electrical Properties of Silicon Nanowires

“…〈111〉 oriented Si wires often show a hexagonal cross section with either {110} or {112} surface facets, 14,16,107,125 as sketched in Figure 12b. According to Ma et al,…”