Microscopic Measurement of Step Movement during Crystal Growth by Chemical Vapor Deposition

Abstract

The design and operating procedure of apparatus for direct microscopic measurement of step movement during crystal growth is presented. The equipment consists of a microscope for observation of growth features, a reaction cell, furnace, and gas-flow control system. The apparatus has been employed to investigate growth mechanisms operative during the deposition of germanium by dissociation of GeI2 in an open tube flow system.

Growth Mechanism of Vapor Deposited Germanium Films

“…In the case of growth of copper whiskers by hydrogen reduction of CuI, it was assumed that reduction did not occur in the vapor phase, but that catalytic reduction of absorbed iodide occurred at the wh~isker tip. For the case of germanium growth, it may be supposed that the reaction at the growth step involves reduction H2(g) + GeI2(g) ~ Ge(s) + 2HI(g) [1] or disproportionation 2GeI~(g) --> GeI4(g) + Ge(s) [2] The step velocity has been shown to be directly pro-port~onal to the GeI2 concentration (Fig. 6) as would be expected either from reaction [1] or [2], where, for example, the rate-controlling step may involve association of a GeI2 molecule with one previously ad-sorbed on the step to yield germanium and the tetraiodide.…”

“…For the case of germanium growth, it may be supposed that the reaction at the growth step involves reduction H2(g) + GeI2(g) ~ Ge(s) + 2HI(g) [1] or disproportionation 2GeI~(g) --> GeI4(g) + Ge(s) [2] The step velocity has been shown to be directly pro-port~onal to the GeI2 concentration (Fig. 6) as would be expected either from reaction [1] or [2], where, for example, the rate-controlling step may involve association of a GeI2 molecule with one previously ad-sorbed on the step to yield germanium and the tetraiodide. It should be possible to distinguish between the predominance of reactions [1] or [2] by determination of rate of step movement at fixed GeI2 pressure under varying hydrogen flow rates.…”

“…The design and operation of the apparatus used to study crystal growth in this investigation have been described previously (2). The equipment consists of a system for carrier gas-flow control and purification, a multistage furnace where formation of gaseous GeI2 occurs, a deposition cell, and a microscope for observation of growth features.…”

Chemical Microscopy

“…This micromanipulator is quite small and a number of them can be mounted on one microscope. Piezoelectric micromanipulators were proposed by Ellis (73), and two very simple, easily made at home, micromanipulators were described by Horwitz and Wood (129) and by Schoenmakers (268). Zanotti (321) described a translating table (mechanical stage) which is particularly useful for histophotometry.…”

“…This model is interesting as a teaching device for demonstrating the behavior of regular crystals, dislocation movements, twinning, and grain boundaries. Seltzer, et al (268) have measured, microscopically, step movements during the growth of Ge crystals by chemical vapor deposition. Keith and Padden (148,149) have studied the spherulitic crystallization of polymers from the melt.…”