Aluminum oxide thin films with or without phosphorus doping were deposited by the atomic layer epitaxy (ALE) technique. The source materials for aluminum were aluminum chloride and aluminum n-propoxide and for oxygen, water and 2-methyl-2-propanol. The phosphorus source was P2O5. The films were analyzed by Rutherford backscattering spectroscopy (RBS), nuclear resonance broadening (NRB), X-ray diffraction (XRD), X-ray fluorescence (XRF), and Fourier transform infrared (FTIR) spectroscopy for chemical composition and structure. The results show that phosphorus can be incorporated in a wide range of concentration levels into the aluminum oxide layers. Greater than 20 wt% doping, however, led to the formation of crystalline aluminum phosphate when the oxygen source was 2-methyl-2-propanol. The phosphorus doping also increased the growth and H3PO4 etch rates of the films.