Effects of lamella preparation on InGaN quantum well luminescence

Despite it being a popular sample preparation technique, the optoelectronic effects of thinning bulk samples into lamella using a Ga-based focused ion beam (FIB), as is commonly performed for studies in a transmission electron microscope, have been seldom studied systematically. In this work, we confront this using correlative cathodoluminescence spectroscopy to investigate the optical properties of high In content c-plane InGaN/GaN quantum wells (QWs), fabricated including a growth-interrupting step that forms regions of quantum disk InGaN islands that behave as localized emitters and, furthermore, reduce the strain-induced quantum Stark effect present in the majority of such heterostructures. Using picosecond electrostatically beam-blanked electron pulses, we measured the decay transients as a function of position and wavelength. The sample was studied before and after undergoing preparation as a lamella, demonstrating that FIB preparation affects both the spectral and temporal luminescence properties despite measures undertaken to protect the sample during fabrication. Non-radiative defects introduced by the ion beam quenched the luminescence as well as reduced the lifetime of emission, with the QW luminescence component particularly affected due to the emission being weakly localized and hence allowing carriers to migrate to defect areas. These findings underscore the importance of correlating bulk and lamella properties to accurately interpret optical measurements.