Direct observation of piezoelectric fields in GaN/ InGaN/GaN strained quantum wells

Area of Science:

• Materials Science
• Solid-State Physics
• Nanotechnology

Background:

• Indium Gallium Nitride (InGaN) quantum wells are crucial for optoelectronic devices.
• Misfit strains in InGaN layers induce piezoelectric fields, impacting device performance.
• Accurate characterization of these electric fields is essential for device optimization.

Purpose of the Study:

• To investigate electric fields within a single InGaN quantum well using off-axis electron holography.
• To quantify the change in mean inner potential (ΔV0) caused by piezoelectric fields.
• To assess the accuracy and limitations of electron holography for studying electric fields in GaN-based structures.

Main Methods:

• Off-axis electron holography was employed to examine a cross-section of a thin InGaN quantum well in Gallium Nitride (GaN).
• Zone axis convergent beam electron diffraction patterns were used to determine crystal polarity.
• Dark-field displacement fringes were utilized to measure the InGaN layer thickness.

Main Results:

• A phase offset was observed across the InGaN quantum well, directly related to specimen thickness under weakly diffracting conditions.
• The relative change in mean inner potential was measured as ΔV0/V0 = 0.042 ± 0.012.
• Thin foil relaxation effects were found to be negligible for the film thicknesses studied.

Conclusions:

• The observed phase offset is attributed to a change in the mean inner potential caused by piezoelectric fields induced by misfit strains.
• The magnitude of the piezoelectric field was determined using measured layer thickness and inner potential changes.
• Electron holography demonstrates potential for accurate electric field studies in GaN structures, with identified limitations.