The determination of both E g of Y2O3 and IL as well as ΔE v of Y2O3/GaN and IL/GaN enables the calculation of the conduction band offset (ΔE c) of Y2O3/GaN, IL/GaN, and Y2O3/IL using the following equation: ΔE c(oxide or IL) = E g(oxide or IL) − ΔE v(oxide/GaN or IL/GaN) − E g(GaN), where E g(GaN) is 3.40 eV for GaN [37]. The obtained values of ΔE c(Y2O3/GaN), ΔE c(IL/GaN), and ΔE c(Y2O3/IL) for all of the investigated samples are presented in Figure 4. In general, a reduction in E g(Y2O3), E g(IL), ΔE c(Y2O3/GaN), and ΔE c(IL/GaN) is observed when different PDA ambients are performed, as indicated by O2 > Ar > FG > N2. The IL has been proven using

XPS to be comprised of a mixture of Ga-O, Ga-O-N, Y-O, and Y-N bonding (HJQ and KYC, unpublished 3-deazaneplanocin A nmr work). The detection of Ga-O and Ga-O-N bonding in the BYL719 concentration region of IL indicates that the oxygen dissociated from Y2O3 during PDA in different ambients would diffuse inward to react with the decomposed GaN substrate. During PDA in O2 ambient, an additional source of oxygen from the gas ambient has contributed to the formation of Ga-O and AZD5153 clinical trial Ga-O-N bonding in the region of IL. Sample subjected to PDA in O2 ambient attains the largest E g(Y2O3) and E g(IL) as well as the highest values of ΔE c(Y2O3/GaN) and ΔE c(IL/GaN). This is related to the supply of O2 from

the gas ambient during PDA, which has contributed to the reduction of oxygen-related defects in the Y2O3 film and the improvement in the compositional homogeneity of the oxide film. The absence of O2 supply during PDA in Ar (inert) and reducing ambient, such as FG and N2, may be the reason contributing to the attainment of lower E g(Y2O3), E g(IL), ΔE c(Y2O3/GaN), and ΔE c(IL/GaN) values than the sample annealed in O2. The presence of N2 in both FG and N2 ambient has caused the formation of O2-deficient Y2O3 film, wherein N atoms dissociated from N2 gas may couple with the oxygen-related defects in the Y2O3 film [30, 38]. In addition, the presence of N2 in both FG and N2 ambient is also capable of performing nitridation process to Janus kinase (JAK) diminish the

tendency of O2 dissociated from the Y2O3 film during PDA to diffuse inward and react with the GaN substrate [30]. Thus, the interfacial layer formed in between the Y2O3/GaN structure for these samples could be O2 deficient. Despite the fact that FG and N2 ambient are capable of providing nitridation and coupling process, the percentage of N2 in FG ambient (95% N2) is lower than that in pure N2. Hence, PDA in N2 ambient will enhance the nitridation process and coupling of N atoms with the oxygen-related defects in Y2O3, which leads to the formation of more O2-deficient Y2O3 film and IL when compared with the sample annealed in FG ambient.