Applicability of Langmuir equation to oxygen pressure dependent photoluminescence from β-Ga2O3 nanostructures

Abstract

β-Ga2O3 nanostructures were synthesized via vapor transport method on gold coated Silicon substrate in N2 ambient. The as synthesized products were investigated by grazing incident X-ray diffraction, scanning electron microscopy and photoluminescence (PL) spectroscopy. It is shown that the intensity of photoluminescence from the ensemble of β-Ga2O3 nanostructures in oxygen gas ambience is correlated with the oxygen pressure through the Langmuir equation. This correlation is found to be reversible and reproducible. This phenomenon, which was not observed in the bulk β-Ga2O3 single crystal, is attributed to the oxygen related shallow trap surface states of the nanostructures with energies at about 4.2 eV above the valance band. Based on the changes in the PL intensity with the oxygen pressures, a possible mechanism for the observed photoluminescence is suggested. The present results provide a route for room-temperature response of oxygen in the gallium oxide nanostructures.

Correlation between surface modification and photoluminescence properties of β-Ga2O3 nanostructures

“…7,[22][23][24] From our previous studies, it is clear that in β-Ga 2 O 3 nanostructures, UV band intensity is more prone to be affected by surface state trapping centers as compared to blue luminescence. 7,8 This is because, the photo excited electrons which give the UV luminescence, are mobile in the conduction band and get trapped at the surface states. In contrast to this, in blue luminescence both the electron and the hole are trapped in the donor and acceptor levels respectively and hence are less prone to surface trapping center.…”

“…19 Dependence of PL intensity on the concentration of oxygen for β-Ga 2 O 3 nanostructures has been reported by the authors previously. 8 The absorption and desorption of the gasses on a surface follows Langmuir equation 20 and hence the PL intensity also changes according to the Langmuir equation. Similar behavior has also been observed in the electrical properties of β-Ga 2 O 3 nanostructure sensors.…”

“…The techniques, used to grow the nanostructures, have a significant influence on the optical sensing properties. Hence, a comprehensive comparative study of different growth techniques like thermal annealing, 25 thermal evaporation [26][27][28] and Vapor transport method 7,8 have been carried out in this work to study the growth induced factors that affect the oxygen sensing of these nanostructures. The dependence of the PL properties as a function of deposition conditions and synthesis techniques are analyzed to optimize the growth process.…”

“…In contrast to this, in blue luminescence both the electron and the hole are trapped in the donor and acceptor levels respectively and hence are less prone to surface trapping center. 7,8 The luminescence intensity and the intensity ratio of the UV to blue luminescence can be used as an important factor to identify the parameters that can degrade the optical response to oxygen gas. The techniques, used to grow the nanostructures, have a significant influence on the optical sensing properties.…”

“…1,[3][4][5][6][7][8] It has attracted significant attention as a transparent conducting oxide in optoelectronics, 9,10 solar blind photo detectors, 11 optical waveguides 12,13 and host material for phosphors. 13,14 Besides this, β-Ga 2 O 3 nanostructures show good sensing properties with a reversible response to oxygen (O 2 ) and CO gases.…”