Cubic boron phosphide epitaxy on zirconium diboride

Cubic boron phosphide (BP) is one of the least studied III-V compound semiconductors, in part because it is difficult to prepare in high quality form. In this study, zirconium diboride (ZrB2) was studied as a potential substrate for BP epitaxial layers, because of its advantages of a low lattice constant mismatch and high thermal stability. Two types of substrates were considered: ZrB2(0 0 0 1) epitaxial films on 4H-SiC(0 0 0 1) and bulk ZrB2(0 0 0 1) single crystals. The optimal temperature for epitaxy on these substrates was 1100 °C; higher and lower temperatures resulted in polycrystalline films. The BP film/ZrB2 interface was abrupt as confirmed by cross-sectional transmission electron microscopy, attesting to the stability of ZrB2 under BP deposition conditions. The BP films were under compressive and tensile strain on ZrB2 and ZrB2/4H-SiC substrates, respectively, as determined by Raman spectroscopy, due to differences in the substrate/film coefficients of thermal expansion. This study suggests that with further optimization, ZrB2 can be an excellent substrate for BP epitaxial films.