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A review on doping with acceptors of pure and structurally perfect HVPE-GaN single crystals grown on the native Ammono-GaN seeds will be described in this paper. Solid iron (Fe), manganese (Mn), magnesium (Mg) or methane (CH4, precursor of carbon) were used as dopant source to crystallize semi-insulating HVPE-GaN. Carbon-doped GaN was highly resistive at room temperature (exceeding 1×108 Ω.cm at 296 K) and became p-type at high temperature. Activation energy of 1 eV was an experimental confirmation of theoretical calculations for CN (deep acceptor). Doping with manganese also led to very high values of resistivity. In this case the activation energy was close to 1.8 eV. Resistivity of GaN with Mn concentration of 1017 cm-3 exceeded 108 Ω.cm at room temperature. Hall measurements revealed n-type conductivity at high temperature. Co-doping of HVPE-GaN with Mn and Mg led to highly resistive material at room temperature (exceeding 1×108 Ω.cm) and p-type at high temperature. The activation energy was 1.2 eV above the maximum of the valence band. GaN doped with Fe was also highly resistive at room temperature (3×107 Ω.cm with free electron concentration of 5×108 cm-3). It showed n-type properties at high temperature and activation energy of around 0.6 eV below the minimum of the conduction band. Structural, optical, and electrical properties of the resulting semi-insulating HVPE-GaN will be examined, presented, and compared in this paper.
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