Thermodynamic and kinetic aspects of AlN crystal formation on (0001)Al₂O₃ surface by ammonia MBE

Abstract

Influence of temperature on AlN formation on (0001) Al2O3 surface under ammonia flux (nitridation process) has been investigated by high‐energy electron diffraction. A significant temperature dependence of AlN formation rate in the temperature range of 850‐940 °C has been found whereas the formation rate is almost constant at temperatures higher than 940 °C. A kinetic scheme of the surface reactions is developed. The values of kinetic constants for the scheme at the low temperature range are found: k1P=6×104exp(‐1.5eV/kT), k2=7×1019exp (‐5.3eV/kT), k3=3×1013exp(‐4eV/kT). For the high temperature range the AlN formation process is described as a surface phase transition in AlN lattice gas. Parameters of lateral interaction between filled AlN cells are determined and the critical temperature of the phase transition is found (Tc=795 °C). (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

2D AlN crystal phase formation on (0001) Al2O3 surface by ammonia MBE

“…Small area sample (4 mm in diameter) was used to decrease the influence of a temperature and ammonia flux inhomogenuity and also to decrease the effect of sapphire surface charging by the primary electron beam of RHEED. More details of the experimental procedure have described earlier [12].…”

“…Also, the decomposition of ammonia on the surface should be taken into account k 3 =k 3 0 exp(-E 3 /kT). In the framework of the mean field approximation a set of kinetic equations for the surface concentrations were obtained [12]. The numeric solution of these equations gives a good agreement with the experimental data if the kinetics constants k i take the following values: k 1 P=6×10 4 exp(-1.5eV/kT), k 2 =7×10 19 exp(-5.3eV/kT), k 3 =3×10 13 exp(-4eV/kT).…”

“…Previously we have reported the investigation of the 2D AlN formation rate as a function of the substrate temperature [12]. In the present work the early stages of the AlN crystal formation on the (0001) Al 2 O 3 surface during nitridation in ammonia molecular beam epitaxy (MBE) have been investigated by the RHEED technique as a function of NH 3 pressure.…”

“…To describe the experimental data a kinetics model was earlier developed in [12]. Obviously, the AlN product formation from Al 2 O 3 and NH 3 reactants is a result of successive chemical reactions on the surface.…”

“…In the present work the early stages of the AlN crystal formation on the (0001) Al 2 O 3 surface during nitridation in ammonia molecular beam epitaxy (MBE) have been investigated by the RHEED technique as a function of NH 3 pressure. The AlN nucleation and growth rate dependence on the ammonia pressure is described in the framework of a developed kinetic model [12]. Evolution of the AlN lattice parameter during nitridation has been also studied.…”