Abstract
Light‐emitting diodes prepared by p‐tipping on n‐type pulled 
substrates are considerably less efficient than those diodes prepared by p‐tipping on solution‐grown substrates. The present study represents an attempt to use chemical etching and optical microscopy to determine the differences between n‐type pulled 
crystals and crystals obtained by solution‐ and vapor‐growth techniques. Etch patterns believed to be associated with impurity precipitates were observed in large numbers in pulled crystals heavily doped (up to 
) with sulfur or tellurium, and to a much lesser extent in lightly doped and undoped pulled crystals. Clusters of small etch pits attributed to isolated precipitates and short etch grooves attributed to decorated dislocations lying parallel to the surface were both observed. These etch patterns were not seen in solution‐grown or vapor‐grown crystals doped to approximately the same carrier concentrations.