Measurement and effects of polarization fields on one-monolayer-thick InN/GaN multiple quantum wells

Polarization fields associated with one-monolayer-thick InN/GaN multiple quantum wells (MQWs) cause shifts of the photoluminescence peak that depend on the GaN barrier layer thickness. Diffraction contrast and aberration-corrected scanning transmission electron microscopy show that the InN QWs are well defined and coherently strained. Mapping of electrostatic potential using off-axis electron holography shows that the electric fields inside the GaN barriers decrease from ∼0.7 to ∼0.2 MV/cm as the barrier layer thickness increases from 5 to 20 nm. Atomistic tight-binding calculations agree closely with experiment, and confirm that changes in optical emission of these III-nitride quantum wells result from changes in the spontaneous and piezoelectric polarization fields in the InN quantum wells and the GaN barrier layers. Overall, this QW system provides the basis for InN-based light-emitting devices operating across a useful band of wavelengths at room temperature.