Recent progress in bulk GaN growth technology will be presented. New results of basic ammonothermal GaN crystallization and halide vapor phase epitaxy (HVPE) of GaN will be shown and analyzed. The advantages, disadvantages and challenges of both methods will be discussed. An influence of lateral growth on critical thicknesses and structural quality of crystallized GaN layers by both methods will be demonstrated. Reduction of lateral crystallization and growth only in one crystallographic direction will be shown.
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.
HVPE can be used for growing thin, up to 200 µm, GaN layers of high purity and low free carrier concentration. Deposition of such material on conductive n-type GaN seeds results in a structure which is the basis of some vertically operating electronic devices. It should be stressed that thickness of this GaN with low free carrier concentration influences the breakdown voltage of the devices. Therefore, HVPE becomes the main epitaxial technology for crystallizing such layers. The method allows to crystalize GaN with a relatively high growth rate of about 100 µm/h. It makes this technology crucial for preparing transistor structures with breakdown voltage higher than a few or several kV. The main goal of this paper is to investigate implantation of beryllium (Be) acceptors into thin (10-100 µm) unintentionally doped layers of GaN crystallized by HVPE on native seeds. A nitride structure comprising of an n-type layer of low free carrier concentration with implanted regions with p-type conductivity or semi-insulating and a highly conductive n-type substrate will be obtained. Basic parameters of HVPE-GaN growth processes (reagent flows, growth temperature) as well as parameters of ion implantation will be determined. Post-implantation damage, which occurs in implanted layers, will be removed by high-temperature (1400-1480°C) annealing at high nitrogen pressure (1 GPa). Basic structural, optical, and electrical parameters of implanted and annealed GaN will be investigated. The samples will be characterized prior to and after ion implantation.
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