Stabilizing detached Bridgman melt crystal growth: Model-based nonlinear feedback control

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Abstract

The dynamics and operability limits of a nonlinear-proportional-integral controller designed to stabilize detached vertical Bridgman crystal growth are studied. The manipulated variable is the pressure difference between upper and lower vapor spaces, and the controlled variable is the gap width at the triple-phase line. The controller consists of a model-based nonlinear component coupled with a standard proportional-integral controller. The nonlinear component is based on a capillary model of shape stability. Perturbations to gap width, pressure difference, wetting angle, and growth angle are studied under both shape stable and shape unstable conditions. The nonlinear-PI controller allows a wider operating range of gain than a standard PI controller used alone, is easier to tune, and eliminates solution multiplicity from closed-loop operation.

Original languageEnglish (US)
Pages (from-to)16-24
Number of pages9
JournalJournal of Crystal Growth
Volume361
Issue number1
DOIs
StatePublished - Dec 15 2012

Keywords

  • A2. Bridgman technique
  • A2. Detached growth
  • A2. Dewetted growth
  • A2. Process control
  • A2. Proportional-integral control
  • B1. Cadmium zinc telluride

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