The formation of the Schottky barrier height (SBH) is a complex problem because of the dependence of the SBH on the atomic structure of the metal-semiconductor (MS) interface. Existing models of the SBH are too simple to realistically treat the chemistry exhibited at MS interfaces. This article points out, through examination of available experimental and theoretical results, that a comprehensive, quantum-mechanics-based picture of SBH formation can already be constructed, although no simple equations can emerge, which are applicable for all MS interfaces. Important concepts and principles in physics and chemistry that govern the formation of the SBH are described in detail, from which the experimental and theoretical results for individual MS interfaces can be understood. Strategies used and results obtained from recent investigations to systematically modify the SBH are also examined from the perspective of the physical and chemical principles of the MS interface.

The physics and chemistry of the Schottky barrier height

III-V semiconductors have high mobility and will be used in field effect transistors with the appropriate gate dielectric. The dielectrics must have band offsets over 1eV to inhibit leakage. The band offsets of various gate dielectrics including HfO2, Al2O3, Gd2O3, Si3N4, and SiO2 on III-V semiconductors such as GaAs, InAs, GaSb, and GaN have been calculated using the method of charge neutrality levels. Generally, the conduction band offsets are found to be over 1eV, so they should inhibit leakage for these dielectrics. On the other hand, SrTiO3 has minimal conduction band offset. The valence band offsets are also reasonably large, except for Si nitride on GaN and Sc2O3 on GaN which are 0.6–0.8eV. There is reasonable agreement with experiment where it exists, although the GaAs:SrTiO3 case is even worse in experiment.

https://www.researchgate.net/file.PostFileLoader.html?id=53ba3e1fd2fd64bc5d8b4653&assetKey=AS%3A273553407053824%401442231622645

Band offsets of high K gate oxides on III-V semiconductors

GaN and AlGaN have shown great potential in next-generation high-power electronic devices; however, they are plagued by a high density of interface states that affect device reliability and performance, resulting in large leakage current and current collapse. In this review, the authors summarize the current understanding of the gate leakage current and current collapse mechanisms, where awareness of the surface defects is the key to controlling and improving device performance. With this in mind, they present the current research on surface states on GaN and AlGaN and interface states on GaN and AlGaN-based heterostructures. Since GaN and AlGaN are polar materials, both are characterized by a large bound polarization charge on the order of 1013 charges/cm2 that requires compensation. The key is therefore to control the compensation charge such that the electronic states do not serve as electron traps or affect device performance and reliability. Band alignment modeling and measurement can help to determi...

Electronic surface and dielectric interface states on GaN and AlGaN

Solution-processed metal-oxide thin films based on high dielectric constant (k) materials have been extensively studied for use in low-cost and high-performance thin-film transistors (TFTs). Here, scandium oxide (ScOx) is fabricated as a TFT dielectric with excellent electrical properties using a novel water-inducement method. The thin films are annealed at various temperatures and characterized by using X-ray diffraction, atomic-force microscopy, X-ray photoelectron spectroscopy, optical spectroscopy, and a series of electrical measurements. The optimized ScOx thin film exhibits a low-leakage current density of 0.2 nA cm−2 at 2 MV cm−1, a large areal capacitance of 460 nF cm−2 at 20 Hz and a permittivity of 12.1. To verify the possible applications of ScOx thin films as the gate dielectric in complementary metal oxide semiconductor (CMOS) electronics, they were integrated in both n-type InZnO (IZO) and p-type CuO TFTs for testing. The water-induced full oxide IZO/ScOx TFTs exhibit an excellent performance, including a high electron mobility of 27.7 cm2 V−1 s−1, a large current ratio (Ion/Ioff) of 2.7 × 107 and high stability. Moreover, as far as we know it is the first time that solution-processed p-type oxide TFTs based on a high-k dielectric are achieved. The as-fabricated p-type CuO/ScOx TFTs exhibit a large Ion/Ioff of around 105 and a hole mobility of 0.8 cm2 V−1 at an operating voltage of 3 V. To the best of our knowledge, these electrical parameters are among the highest performances for solution-processed p-type TFTs, which represents a great step towards the achievement of low-cost, all-oxide, and low-power consumption CMOS logics.

Water-induced scandium oxide dielectric for low-operating voltage n- and p-type metal-oxide thin-film transistors

http://www.phys.ufl.edu/~afh/reprints/SchottkyDiodes_Carbon.pdf

Tuning Schottky diodes at the many-layer-graphene/ semiconductor interface by doping

In this paper, the authors report the nitride surface preparation and growth of these crystalline oxide dielectrics, efforts to improve the oxide/nitride interface properties by reducing the lattice mismatch and accelerated aging effects for these dielectrics on the nitride semiconductors. The authors review progress in obtaining low interface state densities and reducing current collapse with these dielectrics on GaN and examine the thermal stability and compatibility with processing schemes for HEMTs

New Dielectrics for Gate Oxides and Surface Passivation on GaN

The Sc2O3∕GaN interface shows low trap densities and has been used both to demonstrate inversion in gated metal-oxide-semiconductor diodes and to mitigate current collapse in AlGaN∕GaN heterostructure transistors but little is known of the band offsets at this interface. We measured the energy discontinuity in the valence band (ΔEv) of Sc2O3∕GaN heterostructures using x-ray photoelectron spectroscopy. A value of ΔEv=0.42±0.07eV was obtained using the Ga 3d energy level as a reference. With the experimental band gap of 6.0eV for the Sc2O3 grown by this method, this implies that the conduction band offset ΔEC is 2.14eV in this system.

Band offsets in the Sc2O3∕GaN heterojunction system

X-ray photoelectron spectroscopy was used to measure the energy discontinuity in the valence band (ΔEV) of Sm2O3∕GaAs heterostructures in which the Sm2O3 was grown by rf plasma-assisted molecular beam epitaxy on top of GaAs substrates. A value of ΔEV=2.63±0.10eV was obtained by using the Ga 3d energy level as a reference. Given the bandgap of 5.1eV for the Sm2O3, this would indicate a conduction band offset ΔEC of 1.13±0.10eV in this system.

Determination of Sm2O3/GaAs heterojunction band offsets by x-ray photoelectron spectroscopy

The thermal and chemical stability of potential dielectrics for GaN-based devices in a GaN metal organic chemical vapor deposition (MOCVD) environment is investigated, and their suitability for use as a gate dielectric and as a regrowth mask for the selective area growth of GaN is discussed. Thin films of MgO, Sc2O3, and Sc2O3/MgO were grown by molecular beam epitaxy on GaN/sapphire substrates and then annealed in a MOCVD reactor under GaN growth conditions except for the lack of trimethylgallium. All films were processed into metal-oxide-semiconductor diodes and were characterized before and after being annealed using atomic force microscopy, x-ray reflectivity, x-ray photoelectron spectroscopy, current-voltage (I-V), and capacitance-voltage (C-V) measurements. The Gibbs free energy of all possible reactions was calculated, and their probability and possible influence on the characterization results is examined. After being annealed, the atomic force microscopy of the oxide films showed some degree of ro...

A. Gerger

Papers

New Dielectrics for Gate Oxides and Surface Passivation on GaN

Band offsets in the Sc2O3∕GaN heterojunction system

Determination of Sm2O3/GaAs heterojunction band offsets by x-ray photoelectron spectroscopy

Environmental stability of candidate dielectrics for GaN-based device applications

Interfacial differences in enhanced schottky barrier height Au/n-GaAs diodes deposited at 77 K