Hot filament assisted metalorganic vapor-phase deposition of GaN

Abstract

Hot tungsten filament is investigated as an ammonia precracking technique for the low temperature of MOVPE GaN. Samples were grown using different filament temperatures (Tf) and under different (N2, H2) carrier gas compositions. Results were discussed to take one's stand on a thermodynamic analysis of NH3 decomposition as a function of temperature. It appears that the growth kinetics is controlled by the ammonia adsorption for low filament temperatures (< 1200 K) and low nitrogen amounts. For medium Tf (1200-1800 K), the use of hot tungsten filament improves the efficiency of NH3 decomposition and its adsorption on the growth surface. The growth mechanism is controlled by the NH2 adsorption and the ratio of growth rates obtained with and without filament is about 2. High efficiency of ammonia decomposition for Tf > 1800 K results in low growth rate. This was related to NH2 decomposition into atomic nitrogen (N) and hydrogen (H). The recombination of atomic nitrogen before reaching the substrate seems to be significant enough so as to limit the deposition rate. Secondary ion mass spectrometry analysis revealed a decrease in the hydrogen contamination as Tf increases.