We have found that the electrical and optical properties of GaN epilayers strongly depend on the NH3 how rates with Hydrogen dilutions. The growth rate decreases with increasing NH3 flow rate. The electron mobility increased from 90 to 104 cm(2)/Vs as the NH3 flow rate is increased from 1.5 to 2.0 SLM without H-2 dilutions. With NH3 being diluted, the electron mobility can be further increased to 124 cm(2)/Vs. The electron carrier concentration also decreases from 2 x 10(18) to 3.8 x 10(17)cm(-3). The flow patterns can be observed on the surface but becomes more flat and broader after the dilution of NH3. After dilution, the photoluminescence spectra show no evidence of the yellow band emission related to those without NH3 dilution. From detailed FL investigations at temperatures from 12 to 300 K, we find that shallow bound excitons and donor-acceptor pair recombination have stronger emission than yellow band at low temperatures.