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.
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Band alignment of sputtered and atomic layer deposited SiO 2 and Al 2 O 3 on ScAlN
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 deposition more »
- Award ID(s):
- 1856662
- Publication Date:
- NSF-PAR ID:
- 10385645
- Journal Name:
- Journal of Applied Physics
- Volume:
- 132
- Issue:
- 23
- Page Range or eLocation-ID:
- 235701
- ISSN:
- 0021-8979
- Sponsoring Org:
- National Science Foundation
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Valence band offsets for SiO 2 deposited by Atomic Layer Deposition on α -(Al x Ga 1-x ) 2 O 3 alloys with x = 0.26–0.74 were measured by X-ray Photoelectron Spectroscopy. The samples were grown with a continuous composition spread to enable investigations of the band alignment as a function of the alloy composition. From measurement of the core levels in the alloys, the bandgaps were determined to range from 5.8 eV (x = 0.26) to 7 eV (x = 0.74). These are consistent with previous measurements by transmission spectroscopy. The valence band offsets of SiO 2 with these alloys of different composition were, respectively, were −1.2 eV for x = 0.26, −0.2 eV for x = 0.42, 0.2 eV for x = 0.58 and 0.4 eV for x = 0.74. All of these band offsets are too low for most device applications. Given the bandgap of the SiO 2 was 8.7 eV, this led to conduction band offsets of 4.1 eV (x = 0.26) to 1.3 eV (x = 0.74). The band alignments were of the desired nested configuration for x > 0.5, but at lower Al contents the conduction band offsets were negative, with a staggered bandmore »
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The 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 »
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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 .
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The characteristics of sputtered NiO for use in pn heterojunctions with Ga 2 O 3 were investigated as a function of sputtering parameters and postdeposition annealing temperature. The oxygen/ nickel and Ni 2 O 3 /NiO ratios, as well as the bandgap and resistivity, increased as a function of O 2 /Ar gas flow ratio. For example, the bandgap increased from 3.7 to 3.9 eV and the resistivity increased from 0.1 to 2.9 Ω cm for the O 2 /Ar ratio increasing from 1/30 to 1/3. By sharp contrast, the bandgap and Ni 2 O 3 /NiO ratio decreased monotonically with postdeposition annealing temperatures up to 600 °C, but the density of films increased due to a higher fraction of NiO being present. Hydrogen is readily incorporated into NiO during exposure to plasmas, as delineated by secondary ion mass spectrometry measurements on deuterated films. The band alignments of NiO films were type II-staggered gaps with both α- and β-Ga 2 O 3 . The breakdown voltage of NiO/β-Ga 2 O 3 heterojunction rectifiers was also a strong function of the O 2 /Ar flow ratio during deposition, with values of 1350 V for 1/3 and 830 V for 1/30.
