The n-type doping characteristics such as crystallinity, electronic and optical proper;ties of Al0.15Ga0.85N:Si epitaxial layers grown by MOCVD with various Si incorporations have been investigated While the mirror-like surface without any defects such as cracks and hillocks can be seen in the undoped Al0.15Ga0.85N epilayer which was grown without any intentional doping of Si, many cross hatch patterned cracks are observed in the n-Al0.15Ga0.85N:Si which was grown with Si incorporation rate of 1.0nmol/min. The N-type Al0.15Ga0.85N:Si exhibits consistent increase in the electron concentration and decrease in the mobility with raising doping level of Si. The CL spectra of every Si-doped layer show that the donor-to-valence band transition is dominated at 350 mn, which is red shifted by 7 nm against the, band edge luminescence emission of the undoped Al0.15Ga0.85N layer. By calculating the relative intensity between donor-to-band transition of Si-doped Al0.15Ga0.85N and band edge emission of the undoped compound, the change of optical characteristics with different Si,doping levels were evaluated. This result suggested that the cross hatch patterned cracks of the layer which was highly doped by Si are responsible for the abrupt decrease of optical luminescence characteristics. (C) 2002 Elsevier Science B.V. All rights reserved.