The electrical properties of undoped and oxygendoped GaP grown by the liquid encapsulation technique

Abstract

Hall coefficient and conductivity measurements have been made on undoped and oxygen-doped gallium phosphide grown by the liquid encapsulation technique over the temperature range 80 to 400 K. The electrically active impurity in undoped crystals grown from a silica crucible is silicon. The thermal ionization energy of this donor is estimated at 82 meV, which is in good agreement with the optically estimated value. The ionization energy decreases with donor concentration and, to a first approximation, is given (in eV) by E_D = 0082 - 0021 × 10⁻⁶ N_D^{fraction one-third} where N_D is the donor concentration (cm⁻³). Undoped crystals grown from a boron nitride crucible and oxygen-doped crystals grown from a silica crucible have similar electrical properties. The room-temperature carrier concentration in these crystals lies between 5 × 10⁹ and 2 × 10¹⁵ electrons/cm³ and the thermal ionization energies range from 020 to 055 eV. The impurities responsible for these levels have not been identified although it seems likely that oxygen is involved.