Electric-field-induced band bending on GaN: in situ effects of electron beam irradiation on time-dependent cathodoluminescence

Abstract

Electron beam bombardment of GaN has been monitored by secondary electron (SE), cathodoluminescence (CL) imaging, simultaneous in situ CL, and specimen current (SC) measurements. Under extreme irradiation conditions, system perturbations, as seen by SE and time-dependent CL, are attributed to internal charge dynamics extending beyond the scanned areas. Under moderate irradiation conditions, the size of affected regions correlates with nominal scanned regions. Time-dependent CL at the near band edge (NBE) revealed complex interplay with SC, which was modeled through band bending at the Au/GaN interface. The system has shown distinctive internal electric field dynamics upon sample handling, affecting both time-dependent CL spectra and SC as well as producing contrast reversal in SE imaging, to which humidity adsorption could be contributing. The band-bending model presented here can account for both moderate irradiation and humidity effects through variations of depletion widths and Schottky barrier heights. Our findings are consistent with current models where e-beam activated V Ga promotes decreased NBE intensities and C N promotes DL emissions.

Simultaneous specimen current and time-dependent cathodoluminescence measurements on gallium nitride

“…These results resonate with earlier findings reporting SE and CL degraded signals beyond the scanned region due to internal charge dynamics. 14 The steady stored charge values in Fig. 5 mostly vary between 150 and 300 10 -8 C for both 10 and 20keV in all these samples in such a way that cannot explain the τ CL or I CLSS progression in Figures 2 and 4 respectively.…”

“…In this work, simultaneous measurements of NBE CL and specimen current (SC) were conducted as a platform to visualize the interplay of optical properties based on diffusion and leakage currents, the former, believed to be responsible of ultimate failure in operational devices. 3,5,14 Earlier work had confirmed that deep level (DL) emissions remained unaffected, 14 and that surficial carbonaceous impurities were not responsible for decreased NBE signals. 18 In this study, only NBE emissions were monitored from the window regions in LEO GaN films; knowingly, where architected devices down perform those built on the LEO regions.…”

“…5,12 It is worth highlighting that the study of electric fields in insulators is a vibrant field of research. 13 Indeed, electric fields generated in insulators and semiconductors can cause modifications in secondary electron (SE) and back scattered electron (BSE) yields, 14 even during electron beam irradiation in a low pressure SEM. 15 It has previously been shown that absorption of species to the surface can modify band bending and interfacial space charge regions.…”

“…15 It has previously been shown that absorption of species to the surface can modify band bending and interfacial space charge regions. 14 In addition, charging of insulators during electron beam irradiation can lead to x-ray microanalysis artefacts 16 and to electromigration of point defects. 17 Prior works had not considered the effects of electric fields (resulting from prolonged irradiation) on CL signal evolution to enable a distinction between stopping power processes and current density effects.…”

“…increasing the GaN's electron carrier density in the region irradiated by the electron beam) or diffusing beyond the nominal interaction volume, as discussed in Section 2a. 14 The impact of stored charges in NBE CL degradation has not been taken into account in the original discussion by Nykanen et al 5 However, the large amount of stored charge readily available in the nominal interaction volume and beyond (i.e. the space charge region) needs to be taken into account to fully explain CL evolution at later irradiation stages, once the space charge region is established.…”