ZrB 2 Substrate for Nitride Semiconductors

Zirconium diboride (ZrB 2 ) has excellent properties as an electrically conductive substrate for nitride semiconductors. In this paper, the bulk growth of ZrB 2 by a floating-zone method and some properties of ZrB 2 , together with a brief summary of heteroepitaxial growth of gallium nitride (GaN) by molecular beam epitaxy (MBE) and metalorganic vapor phase epitaxy (MOVPE), are presented. By optimizing the bulk growth conditions, a 20-mm-diameter ZrB 2 single crystal was obtained. The cleavage direction of the ZrB 2 (0001) substrate was confirmed to be parallel to [1120], which is parallel to that of GaN (0001). Epitaxial growth by both MBE and MOVPE was demonstrated. The grown n-type GaN/ZrB 2 structure exhibited ohmic-like current–voltage behavior. These results indicate that ZrB 2 has potential for application to the substrate for nitride semiconductors.