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- ECS Journal of Solid State Science and Technology
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X Ray Photoelectron Spectroscopy was used to measure valence band offsets for Al 2 O 3 deposited by Atomic Layer Deposition on α -(Al x Ga 1-x ) 2 O 3 alloys over a wide range of Al contents, x, from 0.26–0.74, corresponding to a bandgap range from 5.8–7 eV. These alloys were grown by Pulsed Laser Deposition. The band alignments were type I (nested) at x <0.5, with valence band offsets 0.13 eV for x = 0.26 and x = 0.46. At higher Al contents, the band alignment was a staggered alignment, with valence band offsets of − 0.07 eV for x = 0.58 and −0.17 for x = 0.74, ie. negative valence band offsets in both cases. The conduction band offsets are also small at these high Al contents, being only 0.07 eV at x = 0.74. The wide bandgap of the α -(Al x Ga 1-x ) 2 O 3 alloys makes it difficult to find dielectrics with nested band alignments over the entire composition range.
The band alignments of two candidate dielectrics for ScAlN, namely, SiO 2 and Al 2 O 2 , were obtained by x-ray photoelectron spectroscopy. We compared the effect of deposition method on the valence band offsets of both sputtered and atomic layer deposition films of SiO 2 and Al 2 O 3 on Sc 0.27 Al 0.73 N (bandgap 5.1 eV) films. The band alignments are type I (straddled gap) for SiO 2 and type II (staggered gap) for Al 2 O 3 . The deposition methods make a large difference in relative valence band offsets, in the range 0.4–0.5 eV for both SiO 2 and Al 2 O 3 . The absolute valence band offsets were 2.1 or 2.6 eV for SiO 2 and 1.5 or 1.9 eV for Al 2 O 3 on ScAlN. Conduction band offsets derived from these valence band offsets, and the measured bandgaps were then in the range 1.0–1.1 eV for SiO 2 and 0.30–0.70 eV for Al 2 O 3 . These latter differences can be partially ascribed to changes in bandgap for the case of SiO 2 deposited by the two different methods, but not for Al 2 O 3 , where the bandgap as independent of depositionmore »
The band alignment of Atomic Layer Deposited SiO2on (InxGa1−x)2O3at varying indium concentrations is reported before and after annealing at 450 °C and 600 °C to simulate potential processing steps during device fabrication and to determine the thermal stability of MOS structures in high-temperature applications. At all indium concentrations studied, the valence band offsets (VBO) showed a nearly constant decrease as a result of 450 °C annealing. The decrease in VBO was −0.35 eV for (In0.25Ga0.75)2O3, −0.45 eV for (In0.42Ga0.58)2O3, −0.40 eV for (In0.60Ga0.40)2O3, and −0.35 eV (In0.74Ga0.26)2O3for 450 °C annealing. After annealing at 600 °C, the band alignment remained stable, with <0.1 eV changes for all structures examined, compared to the offsets after the 450 °C anneal. The band offset shifts after annealing are likely due to changes in bonding at the heterointerface. Even after annealing up to 600 °C, the band alignment remains type I (nested gap) for all indium compositions of (InxGa1−x)2O3studied.
In situ MOCVD growth and band offsets of Al 2 O 3 dielectric on β-Ga 2 O 3 and β-(Al x Ga 1−x ) 2 O 3 thin filmsThe in situ metalorganic chemical vapor deposition (MOCVD) growth of Al 2 O 3 dielectrics on β-Ga 2 O 3 and β-(Al x Ga 1−x ) 2 O 3 films is investigated as a function of crystal orientations and Al compositions of β-(Al x Ga 1−x ) 2 O 3 films. The interface and film qualities of Al 2 O 3 dielectrics are evaluated by high-resolution x-ray diffraction and scanning transmission electron microscopy imaging, which indicate the growth of high-quality amorphous Al 2 O 3 dielectrics with abrupt interfaces on (010), (100), and [Formula: see text] oriented β-(Al x Ga 1−x ) 2 O 3 films. The surface stoichiometries of Al 2 O 3 deposited on all orientations of β-(Al x Ga 1−x ) 2 O 3 are found to be well maintained with a bandgap energy of 6.91 eV as evaluated by high-resolution x-ray photoelectron spectroscopy, which is consistent with the atomic layer deposited (ALD) Al 2 O 3 dielectrics. The evolution of band offsets at both in situ MOCVD and ex situ ALD deposited Al 2 O 3 /β-(Al x Ga 1−x ) 2 O 3 is determined as a function of Al composition, indicating the influence of themore »
There is increasing interest in α-polytype Ga 2 O 3 for power device applications, but there are few published reports on dielectrics for this material. Finding a dielectric with large band offsets for both valence and conduction bands is especially challenging given its large bandgap of 5.1 eV. One option is HfSiO 4 deposited by atomic layer deposition (ALD), which provides conformal, low damage deposition and has a bandgap of 7 eV. The valence band offset of the HfSiO 4 /Ga 2 O 3 heterointerface was measured using x-ray photoelectron spectroscopy. The single-crystal α-Ga 2 O 3 was grown by halide vapor phase epitaxy on sapphire substrates. The valence band offset was 0.82 ± 0.20 eV (staggered gap, type-II alignment) for ALD HfSiO 4 on α-Ga 0.2 O 3 . The corresponding conduction band offset was −2.72 ± 0.45 eV, providing no barrier to electrons moving into Ga 2 O 3 .