Al Composition Dependence of Band Offsets for SiO2 on α-(AlxGa1-x)2O3

Valence band offsets were measured by X Ray Photoelectron Spectroscopy for SiO2 deposited by Atomic Layer Deposition on α-(AlxGa1-x)2O3 alloys with x= 0.26-0.74 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 7eV (x=0.74). The valence band offsets 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. Given the bandgap of the SiO2 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 nested for x>0.5 , but at lower Al contents the conductions band offsets were negative, with a staggered band alignment. This shows the challenge of finding appropriate dielectrics for this ultra-wide bandgap semiconductor system.

Direct calculations on the band offsets of large-lattice-mismatched and heterovalent Si and III–V semiconductors

Band offset in semiconductors is a fundamental physical quantity that determines the performance of optoelectronic devices. However, the current method of calculating band offset is difficult to apply directly to the large-lattice-mismatched and heterovalent semiconductors because of the existing electric field and large strain at the interfaces. Here, we proposed a modified method to calculate band offsets for such systems, in which the core energy level shifts caused by heterovalent effects and lattice mismatch are estimated by interface reconstruction and the insertion of unidirectional strain structures as transitions, respectively. Taking the Si and III–V systems as examples, the results have the same accuracy as what is a widely used method for small-lattice-mismatched systems, and are much closer to the experimental values for the large-lattice-mismatched and heterovalent systems. Furthermore, by systematically studying the heterojunctions of Si and III–V semiconductors along different directions, it is found that the band offsets of Si/InAs and Si/InSb systems in [100], [110] and [111] directions belong to the type I, and could be beneficial for silicon-based luminescence performance. Our study offers a more reliable and direct method for calculating band offsets of large-lattice-mismatched and heterovalent semiconductors, and could provide theoretical support for the design of the high-performance silicon-based light sources.

Computing with DFT Band Offsets at Semiconductor Interfaces: A Comparison of Two Methods

Two DFT-based methods using hybrid functionals and plane-averaged profiles of the Hartree potential (individual slabs versus vacuum and alternating slabs of both materials), which are frequently used to predict or estimate the offset between bands at interfaces between two semiconductors, are analyzed in the present work. These methods are compared using several very different semiconductor pairs, and the conclusions about the advantages of each method are discussed. Overall, the alternating slabs method is recommended in those cases where epitaxial mismatch does not represent a significant problem.