Band Alignment of Atomic Layer Deposited SiO₂ and Al₂O₃ on (Al_xGa_1-x)₂O₃ for x = 0.2-0.65

Abstract

(AlxGa1-x)2O3 is attracting attention for use in heterostructure devices grown on Ga2O3 substrates. The band alignments of amorphous, atomic layer deposited Al2O3 and SiO2 on (AlxGa1-x)2O3 for x = 0.2-0.65 have been determined using high resolution X-ray photoelectron spectroscopy. The (AlxGa1-x)2O3 was grown by continuous composition spread Pulsed Laser Deposition (CCS-PLD). The band alignments are type I (nested gap) in all cases, with conduction band offsets ranging from 1.57-0.67 eV for Al2O3 on (Al0.2Ga0.8)2O3 to (Al0.65Ga0.35)2O3 and 2.35-1.40 eV for SiO2 on these same compositions. Correspondingly, the valence band offsets are all >1.25 eV for SiO2 and 0.23-0.33eV for Al2O3 over this composition range. While these are the first reports for Al2O3 on (AlxGa1-x)2O3 over such a wide composition range, our results differ by up to 0.4 eV in conduction band offsets from past studies of SiO2 on (AlxGa1-x)2O3 of a more limited composition range, which themselves have shown variations of up to 0.5eV for conduction band offsets on nominally the same composition. These differences emphasize the influence of experimental conditions in determining band alignments.

Band Offsets at κ-([Al,In]xGa1–x)2O3/MgO Interfaces

“…Conduction band offsets of at least 1.4 eV for all compositions provide excellent carrier confinement for electrons exceeding the required 1 eV recommended in literature for MOS transistors 59 . The magnitude of these offsets is similar to those of established dielectrics such as SiO2, Al2O3, HfO2 or HfSiO4 to various other polymorphs of the (AlxGa1-x)2O3/(InxGa1x)2O3 alloy systems [60][61][62] . Therefore, this material might be a promising alternative to these established gate dielectrics in HEMT or other field-effect transistor applications based on Ga2O3, as also recently suggested for the monoclinic modification 63 .…”

A Generalized Semiempirical Approach to the Modeling of the Optical Band Gap of Ternary Al-(Ga, Nb, Ta, W) Oxides Containing Different Alumina Polymorphs

“…(a) Band gap values of β-(Ga (1– x ) Al x ) 2 O 3 ternary system vs Al content (0.11 ≤ x Al ≤ 0.81) for experimental data points (polycrystalline powders and PLD films) derived from the REELS (circles and diamonds) technique and Tauc plot from optical absorption measurements on the PLD film (triangles, see text). (b) Experimental band gap values from REELS data of β-(Ga (1– x ) Al x ) 2 O 3 ternary system vs Al content (0.11 ≤ x Al ≤ 0.81) (blue circles).…”

“…Much more complications arise for the second pseudoregular ternary system β-(Ga (1– x ) Al x ) 2 O 3 since largely variable E g values have been reported in the literature for the band gap of β-Ga 2 O 3 (4.4–5.0 eV) ,,− as well as for ternary β-(Ga (1– x ) Al x ) 2 O 3 mixed oxides as a function of different methods of preparation and techniques of evaluation of the band gap. − ,,,− Usually, lower optical band gap values are measured in the Tauc plot by assuming indirect optical transitions, while larger values are measured in the hypothesis of direct optical transitions . Still, different values have been reported in the case of E g values estimated by using ellipsometry or the REELS technique. ,,− In some cases, nearly identical E g values have been reported by using REELS or the Tauc method of determination of band gap, but large scattering of data has been reported from the same laboratory. , …”

“…As for the fitting of β-(Ga (1– x ) Al x ) 2 O 3 experimental data, in Figure a, we reported the experimental E g data of β-(Ga (1– x ) Al x ) 2 O 3 films of variable composition and deposited by different techniques: atomic layer deposition (ALD), pulsed laser deposition (PLD), and RF-magnetron sputtered deposition. ,− …”

“…On the other hand, the data represented by triangle and diamond symbols in Figure a pertain to PLD films and crystalline powders, respectively, for which the band gap values have been obtained by the same REELS technique. , The E g,REELS vs x Al data set (dark blue symbols in Figure b) pertaining to both polycrystalline powders and PLD films will be assumed as the “reference data set” owing to the larger interval of composition covered (0.11 ≤ x ≤ 0.81) as well as to the good reproducibility of the REELS data derived from different laboratories and for samples grown by different techniques.…”