Ammonia molecular beam epitaxy growth of p-type GaN and application to bipolar junction transistors

We have investigated the effect of the growth temperature and magnesium flux on Mg incorporation in ammonia-MBE grown GaN epilayers. Secondary ion mass spectroscopy revealed that the incorporation of Mg is more sensitive to the growth temperature than to Mg flux. Simultaneously, the available amount of Mg at the substrate surface has to be accurately balanced in order to achieve the optimum electrical (p∼3×1017cm−3, μ∼12cm2∕Vs, ρ∼2ohmcm) and structural properties [ω-scan FWHM(0002)∼550arcsec]. The surface morphology of the Mg-doped GaN epilayers, using various growth temperatures and Mg fluxes, has been studied by atomic force microscopy showing a considerable change in the GaN average grain size. The optimum growth window for achieving high quality, p-type conductivity in GaN using ammonia-MBE will be discussed. As an application, n–p–n bipolar junction transistors were grown and fabricated. A current gain of 10 with VBC=0V was achieved using these devices.