Profiling band structure in GaN devices by electron holography

Electron holography in a field emission gun transmission electron microscop e has been used to profile the inner potential V-0 across GaN/x nm In0.1Ga0 .9N/GaN/(0001) sapphire samples (x=10. 40nm) grown by molecular beam epitax y and viewed in cross-section. Results are presented which suggest a decrea se in V-0 of 3-4 V across the InGaN layer in the [0001] direction. It is pr oposed that the results can be explained by charge accumulation across the InGaN layer and that the opposing contributions due to piezoelectric and po larisation fields are effectively masked by Fermi level pinning. (C) 2001 E lsevier Science B.V. All rights reserved.