Plasma assisted molecular beam epitaxy of GaN with growth rates >2.6 µm/h

Abstract

Plasma-assisted molecular beam epitaxial (PAMBE) growth of gallium nitride (GaN) was explored with a novel modification of a commercially available nitrogen plasma source. The modified nitrogen plasma source enabled a dramatic increase in the flux of active nitrogen and thus a significantly higher growth rate than has been previously reported. GaN films were grown using N2 gas flow rates between 1 and 8sccm while varying the plasma source's RF forward power from 200 to 600W. The highest growth rate, and therefore the highest active nitrogen flux achieved was ~2.65μm/h. For optimized growth conditions the surfaces displayed a clear step-terrace structure with an average RMS roughness (3µm×3µm) on the order of 1nm. Secondary ion mass spectroscopy (SIMS) impurity analysis demonstrates oxygen and hydrogen incorporation of 1×1016 and 5×1016 respectively, comparable to the metal organic chemical vapor deposition (MOCVD) grown template layer. Initial un-optimized electron mobility measurements of 1µm thick GaN layers have shown a peak mobility of ~705cm2/Vs for an electron concentration of ~3.5×1016cm−3. A revised universal growth diagram is proposed allowing the rapid determination of the metal flux needed to grow in a specific growth regime for any and all active nitrogen fluxes available.