Electron Enhanced Growth of Crystalline Gallium Nitride Thin Films at Room Temperature and 100 °C Using Sequential Surface Reactions.

Low energy electrons may provide mechanisms to enhance thin film growth at low temperatures. As a proof of concept, this work demonstrated the deposition of gallium nitride (GaN) films over areas of ∼5 cm2 at room temperature and 100 °C using electrons with a low energy of 50 eV from an electron flood gun. The GaN films were deposited on Si(111) wafers using a cycle of reactions similar to the sequence employed for GaN atomic layer deposition (ALD). Trimethylgallium (Ga(CH3)3, TMG), hydrogen (H) radicals and ammonia (NH3) were employed as the reactants with electron exposures included in the reaction cycle after the TMG/H and NH3 exposures. A number of ex situ techniques were then employed to analyze the GaN films. Spectroscopic ellipsometry measurements revealed that the GaN films grew linearly with the number of reaction cycles. Linear growth rates of up to 1.3 Å/ cycle were obtained from the surface areas receiving the highest electron fluxes. Grazing incidence X-ray diffraction analysis revealed polycrystalline GaN films with the wurtzite crystal structure. Transmission electron microscopy (TEM) images showed crystalline grains with diameters between 2 and 10 nm depending on the growth temperature. X-ray photoelectron spectroscopy depth-profiling displayed no oxygen contamination when the GaN films were capped with Al prior to atmospheric exposure. However, the carbon concentrations in the GaN films were 10-35 at. %. The mechanism for the low temperature GaN growth is believed to result from the electron stimulated desorption (ESD) of hydrogen. Hydrogen ESD yields dangling bonds that facilitate Ga-N bond formation. Mass spectrometry measurements performed concurrently with the reaction cycles revealed increases in the pressure of H2 and various GaN etch products during the electron beam exposures. The amount of H2 and GaN etch products increased with electron beam energy from 25 to 200 eV. These results indicate that the GaN growth occurs with competing GaN etching during the reaction cycles.