Mapping of the electrostatic potentials in MOCVD and hybrid GaN tunnel junctions for InGaN/GaN blue emitting light emitting diodes by off-axis electron holography correlated with structural, chemical, and optoelectronic characterization

Off-axis electron holography has been used to measure the width of the depletion region in a series of tunnel junction GaN light emitting diodes that have been prepared using different growth processes for blue emission. The total measured potentials are combinations of the mean inner potential, dopant potential, and piezoelectric contributions. The dopant potential has been unmixed from the mean inner potential such that the width of the tunnel junctions in the different diodes can be measured. The experimental results are then compared to secondary ion mass spectrometry, simulations, and opto-electronic testing. We find that the measured tunnel junction widths are consistent with simulations as well as the current density and voltage characteristics. As such, off-axis electron holography has been demonstrated as a unique technique that can be used to reproducibly measure the electrostatic potentials in tunnel junctions with nm-scale resolution in real III-V device specimens.