Abstract
The Ga concentration in 
crystals prepared by a variety of techniques (pulled by the liquid encapsulation Czochralski technique from stoichiometric or nonstoichiometric melts, solution grown, and annealed) has been determined by precision coulometric titration, yielding the experimental solidus boundary which exhibits an excess of Ga along the Ga‐rich liquidus. Based on a thermodynamic model, assuming that neutral Ga and P vacancies are the predominant native defects, the analysis of the solidus data permitted the evaluation of the vacancy concentrations over a wide temperature range. At the melting point of 
(1465°C) there are 8 × 1018 and 1.3 × 1019 cm−3 Ga and P vacancies, respectively, in the crystal. The calculated solidus curve well represents the totality of experimental data and shows retrograde temperatures at 1375° and 1400°C on the Ga‐ and P‐rich sides, respectively. The enthalpies and entropies associated with vacancy formation are given and discussed. It is shown that the data provide strong additional support to the previous identification of Ga vacancies with killer centers in 
.