Photoadsorption and photodesorption for GaN

Abstract

Local conductivity and surface photovoltage variations due to magnesium segregation in p-type GaNThe effect of an ambient environment on the surface photovoltage and photoluminescence observed for GaN is studied. In air ambient the upward band bending gradually increases under UV illumination and is explained by the photoinduced chemisorption of surface adsorbates. Specifically, the increase in negative surface charge is consistent with the transfer of electrons from surface states or bulk to oxygen species physisorbed at the GaN surface. In contrast, the upward band bending gradually decreases in vacuum under UV illumination and can be explained by the photoinduced desorption of these species. The photoadsorption and photodesorption of negatively charged species cause the surface depletion region to increase and decrease, respectively. This change in depletion region width is consistent with the observed decrease in photoluminescence intensity in air ambient and its significant increase in vacuum for a sample with low free electron concentration.

Direct assessment of p–n junctions in single GaN nanowires by Kelvin probe force microscopy

“…After illumination is switched off the p and n sides do not recover immediately their original potential value. A similar behavior has been analyzed by Foussekis et al [22] in not-intentionally doped bulk GaN, and attributed to a slow electron transfer process between the chemisorbed oxygen and the GaN surface by tunneling through the thin surface oxide layer. We can estimate the effect of surface band bending on the n-type NW by taking into account the results of the simulation, where the surface barrier for a NW with a diameter of 50 nm is determined to be 0.5 eV.…”

Oxygen photo-adsorption related quenching of photoluminescence in group-III nitride nanocolumns

“…Instead, the signal reached 60% of its maximum within a few seconds and, then only, it started decaying, finally reaching 10% of the maximum value. This result is in favor of a photo-adsorption mechanism [20].…”

“…This quenching dynamics suggests some self-limited chemisorption process in which photo-created free carriers are involved in the adsorption of species at the surface. The accumulation of those species with time raises a potential barrier [1,20] thus hindering further access of free carriers to the surface, which therefore limits additional adsorption.…”

“…Now, the high effective surface of dense NC assemblies suggests that surface should play a much more prominent role than in planar structures. As an example of such surface effects, in undoped GaN planar epilayers, Foussekis et al [20] recently reported that photo-adsorption of oxygen causes significant quenching of the RT PL. This was explained by the upward bending of the near-surface potential, which is increased by the photo-induced adsorption of species in air ambient.…”

High-temperature ultraviolet detection based on surface photovoltage effect in SiN passivated n-GaN films

“…The dielectric films were used to prevent the reactive GaN surface from the interaction with species in air ambient and uncontrolled formation of native oxides as well as to avoid the photo-induced adsorption/desorption effects under UV illumination. 8 It should be noted that there is no reports on the SPV effect in GaN covered with dielectric films.…”