We report the molecular beam epitaxial (MBE) growth of high quality epitaxial indium phosphide (InP) using a valved phosphorus cracker cell over a wide range of V/III flux ratio (1.2-9.3) and substrate temperature (360 degrees C to 500 degrees C). The as-grown epitaxial InP on InP (100) substrate was n-type, with a background electron concentration and mobility which varied according to the V/III flux ratio and substrate temperature (T-s). Using a cracking zone temperature (T-cr) of 850 degrees C, the highest electron mobility at 77 K of 40900 cm(2)/Vs was achieved at a V/III flux ratio of 2.3 at a substrate temperature of 440 degrees C. The corresponding background electron concentration at 77 K was the lowest at 1.74 x 10(15) cm(-3). The photoluminescence (PL) full-width at half maximum (FWHM) decreased significantly in samples grown at lower flux ratios indicating an improvement in the optical quality.