  Unlike non-polar semiconductors such as silicon, the broken inversion
symmetry of the wide bandgap semiconductor gallium nitride leads to a large
electronic polarization along a unique crystal axis. This makes the two
surfaces of the semiconductor wafer perpendicular to the polar axis
dramatically different in their physical and chemical properties. In the last
three decades, the cation (gallium) face of gallium nitride has been used for
photonic devices such as LEDs and lasers. Though the cation face has also been
predominantly used for electronic devices, the anion (nitrogen) face has
recently shown promise for high electron mobility transistors due to favorable
polarization discontinuities. In this work we show that it is possible to make
photonic devices on the cation face, and electronic devices on the anion face,
of the same semiconductor wafer. This opens the possibility for dualtronics in
polar semiconductors, where electronic, photonic, and acoustic properties can
be implemented on opposite faces of the same wafer, dramatically enhancing the
functional capabilities of this revolutionary semiconductor family.
