Talk abstract

In this talk, we cover three main results from our work on the optimization of MBE grown Mg-doped GaN: (1) optimization of growth conditions and resulting morphology; (2) transport properties and abruptness of doping; and (3) polarity inversion as a result of Mg doping. For these studies Mg layers were grown by plasma-assisted molecular-beam epitaxy at 650 °C . In the plasma-assisted MBE growth of nitrides, we show that optimal growth is realized for Ga-rich conditions at the cross-over from a Ga-wetting layer on the surface to conditions that give rise to droplets on the GaN surface. Growth under N-rich conditions resulted in either semi-insulating or n-type material. Secondary-ion-mass-spectroscopy measurements reveal uniform Mg doping profiles with very sharp boundaries. The amount of incorporated Mg atoms changes approximately linearly with incident Mg flux. Hall measurements on p-type GaN:Mg layers show that about 1%-2% of all Mg atoms are ionized at room temperature. The hole mobility depends strongly on the hole concentration, varying from mu_p = 24 cm2/ Vs for p = 1.8 x 10E17 cm-3 to mu_p = 7.5 cm2/ Vs for p = 1.4 x 10E18 cm-3 . We have carried extensive studies on the polarity inversion that results from Mg-doping. We show that under N-rich conditions, the polarity can be completed inverted by Mg, whereas Ga-rich conditions result in the formation of 'spiked-shape' inversion domains.