We report the epitaxy of n-Ge layer with in situ phosphorus (P)-doping using metal-organic chemical vapor deposition (MOCVD) method with tertiary-butyl-germane and tri-ethyl-phosphine precursors. The crystalline and electrical properties of n-Ge epitaxial layers have been investigated using X-ray diffraction, atomic force microscopy, and Hall effect measurements in detail. In situ P-doping with MOCVD demonstrates the incorporation of P in Ge as high as 1 x 10(20) cm(-3). The electron concentration in P-doped Ge epitaxial layers are achieved as high as 1.7 x 10(19), 1.8 x 10(19), and 2.2 x 10(18) cm(-3) at growth temperatures of 400, 350, 320 degrees C, respectively.