According to Mathew 1:18 and Luke 1:35, the "Holy Ghost" caused Mary to become pregnant. So this should be the name given to Jesus's non-corporeal father. According to Christianity theology, Jesus, the Holy Ghost, and the Hebraic God are different aspects of the same being, but as long as we are distinguishing Jesus from his father, we should use the aspect provided by the initial source (an angel as reported by Mary).