TABLE OF CONTENTS Semiconductor crystals, including GaAs, are grown from a liquid "melt" with a small single crystal "seed" used as the starting material. An ingot or boule of material is grown from the seed as it is pulled from the melt and the interface between the melt and the crystal forms a growing surface. The melt is confined in an enclosed area constrained in ways defined by the specific method of growth and is usually grown as a boule that is one to several times longer than the diameter of the wafer desired. After growth, the boule is removed from the crucible (container), ground to the desired diameter, and sliced into wafers which are lapped and polished. Electronic devices require high-resistivity semi-insulating GaAs (>10 7 ?-cm) in contrast to many photonic devices, which generally require doped substrates. Ideally, GaAs wafers are extremely pure and free of defects. In practice, GaAs wafers do have reasonably high purity (7 8 orders of magnitude lower impurity concentration than the effective GaAs "concentration"). However, temperature non-uniformities that exist both at the growth front and during the cooling process cause stresses in the GaAs crystal, which lead to the formation of dislocations. Most of the art in GaAs growth is aimed at producing economical, high-yield substrates with both radial and axial uniformity while minimising dislocations and achieving uniform high resistivity. Other parameters of interest for the sliced wafer include flatness and surface preparation for epitaxial growth (Section 2.4). As if these were not...
