MOCVD epitaxy of β-(Al_xGa_(1-x))_2O_3 thin films on (010) Ga_2O_3 substrates and N-type doping

摘要

(010) beta-(AlxGa1-x)(2)O-3 thin films were grown on (010) beta-Ga2O3 substrates via metalorganic chemical vapor deposition with up to 40% Al incorporation by systematic tuning of the Trimethylaluminum (TMAl)/triethylgallium molar flow rate ratio and growth temperature. High crystalline quality with pure beta-phase (AlxGa1-x)(2)O-3 was achieved for films with Al composition x < 27%, while a higher Al composition induced phase segregation which was observed via X-ray diffraction spectra. Al incorporation was highly dependent on the growth temperature, chamber pressure, oxygen partial pressure, and TMAl molar flow rate. Atomic resolution scanning transmission electron microscopy (STEM) imaging demonstrated a high crystalline quality beta-(Al0.15Ga0.85)(2)O-3 film with an epitaxial interface. High resolution STEM imaging of (AlxGa1-x)(2)O-3/Ga2O3 superlattice (SL) structures revealed superior crystalline quality for the 23% Al composition. When the Al composition reaches 40%, the SL structure maintained the beta-phase, but the interfaces became rough with inhomogeneous Al distribution. N-type doping using Si in beta-(AlxGa1-x)(2)O-3 films with the Al composition up to 33.4% was demonstrated.