Diffusion of Mg from Mg-ion-implanted GaN layer to metalorganic chemical vapour deposition re-grown AlGaN/GaN layers was detected and identified as a critical problem in devices which were dependent upon layers implanted with Mg for its current blocking properties. Surface treatments done to etch away the Mg rich layer prior to the re-growth was not beneficial unlike in the case of the GaN doped with Mg. Remarkably, re-growth of a sub-nanometer thick (7Å) AlN layer on top of the Mg-implanted GaN was found to be effective in arresting the Mg from diffusing out into the AlGaN/GaN layers grown on top at 1160C. This was verified from both secondary ion mass spectrometry analysis and electrical (capacitance-voltage) data. This result was significant because at such thickness the AlN would not impact the crystal quality of the overgrown material and served as a viable method of achieving a current blocking structure by metalorganic chemical vapour deposition growth.

Use of Sub-Nanometer Thick AlN to Arrest Diffusion of Ion-Implanted Mg into Regrown AlGaN/GaN Layers. S.Chowdhury, B.L.Swenson, J.Lu, U.K.Mishra: Japanese Journal of Applied Physics, 2011, 50[10], 101002