Measurement of electric field across individual wurtzite GaN quantum dots using electron holography

Electrostatic potential profiles across wurtzite AlN/GaN quantum dot (QD) superlattices grown by molecular beam epitaxy have been measured using off-axis electron holography. The profiles for individual GaN QDs show large phase shifts which can be understood in terms of spontaneous polarization and piezoelectric fields and the accumulation of positive and negative charge at the GaN/AlN interfaces. An electric field with magnitude of ∼7.8 ± 2 MV/cm was measured across the center of a GaN QD, in reasonable agreement with reported simulations.