AlN crystal by Slack and McNelly [J. Crystal Growth 34, 263 (1976)]. Scale is shown in cm.

The current development of III-nitride epitaxy provides many possible applications using these wide band gap and high temperature semiconductors. These applications include the development of blue/uv solid state charge injection lasers, high power and high temperature applications. However, at the present time, a suitable substrate for III-nitride epitaxy has not been developed.

With the advent of the gallium nitride devices there is a need for high quality crystal substrates on which to grow the active GaN epitaxial layers. The best possible substrate would be large area GaN single crystal wafers, but there is no known current technology by which such crystals can be grown. The next-best possible substrate is aluminum nitride. All the other possible substrates have serious disadvantages. The sublimation-recondensation method of growing AlN boules was worked out twenty years ago by Slack and McNelly. We have already grown GaN epitaxial films of good quality on such AlN crystals. These AlN substrates have only a 2.2% lattice mismatch with GaN, and have an almost identical thermal expansion curve versus temperature. They also have the same wurtzite crystal structure as GaN and the same kind of piezoelectric polarity. In contrast Al2O3 substrates have zero polarity and can give rise to +/- c-axis domains in epitaxial films of GaN.

Last updated on 5/30/97