Energy band offsets of dielectrics on InGaZnO4

Abstract

Thin-film transistors (TFTs) with channels made of hydrogenated amorphous silicon (a-Si:H) and polycrystalline silicon (poly-Si) are used extensively in the display industry. Amorphous silicon continues to dominate large-format display technology, but a-Si:H has a low electron mobility, l $ 1 cm 2 /V s. Transparent, conducting metal-oxide materials such as Indium-Gallium-Zinc Oxide (IGZO) have demonstrated electron mobilities of 10-50 cm 2 /V s and are candidates to replace a-Si:H for TFT backplane technologies. The device performance depends strongly on the type of band alignment of the gate dielectric with the semiconductor channel material and on the band offsets. The factors that determine the conduction and valence band offsets for a given material system are not well understood. Predictions based on various models have historically been unreliable and band offset values must be determined experimentally. This paper provides experimental band offset values for a number of gate dielectrics on IGZO for next generation TFTs. The relationship between band offset and interface quality, as demonstrated experimentally and by previously reported results, is also explained. The literature shows significant variations in reported band offsets and the reasons for these differences are evaluated. The biggest contributor to conduction band offsets is the variation in the bandgap of the dielectrics due to differences in measurement protocols and stoichiometry resulting from different deposition methods, chemistry, and contamination. We have investigated the influence of valence band offset values of strain, defects/vacancies, stoichiometry, chemical bonding, and contamination on IGZO/dielectric heterojunctions. These measurements provide data needed to further develop a predictive theory of band offsets. Published by AIP Publishing.

Tailoring the Band Alignment of Gax Zn1-x O/InGaZnO Heterojunction for Modulation-Doped Transistor Applications

“…In recent years, the thin‐film transistor (TFT) based on amorphous oxide semiconductor (AOS) have made an impressive progress for the applications in flat‐panel displays (FPDs), for example, active‐matrix liquid‐crystal display (AMLCD) and active‐matrix organic‐light‐emitting‐diode display (AMOLED) . Among them, amorphous InGaZnO (a‐IGZO) TFT is commonly used owing to its relatively high field‐effect mobility (µ FE , ≈10 cm 2 s −1 v −1 ) . However, the µ FE of a‐IGZO TFTs is still not high enough for more advanced applications such as three‐dimensional (3D) displays, flexible logic circuits, and system‐on‐panel devices …”

Device processing and junction formation needs for ultra-high power Ga2O3 electronics

“…[55][56][57][58][59][60] There are often variations in reported valence band offsets for dielectrics on semiconductors and some of the reasons documented include metal or carbon contamination, interfacial disorder, variations in dielectric composition, thermal conditions, strain, and surface termination effects. [59] Figure 10 shows there are differences of up to 1 eV in band alignments for SiO 2 and Al 2 O 3 on Ga 2 O 3 and (Al 0.14 Ga 0.86 ) 2 O 3 , depending on whether they are deposited by sputtering or Atomic Layer Deposition. In the case of Al 2 O 3 , this changed the band alignment from nested (type I) to staggered gap (type II).…”

Determination of the Band Alignment of a‐IGZO/a‐IGMO Heterojunction for High‐Electron Mobility Transistor Application

“…Furthermore, the carrier confinement and transport properties of a heterostructure depend on the band alignment of the buried interface, or equivalently on the Δ E C and Δ E V . XPS is a well‐established approach for the determination of band alignments of heterojunctions . Using XPS, the electrostatic potential at the interface can be monitored.…”

“…Finally, high‐resolution survey scans with the step of 0.01 eV and pass energy of 20 eV were performed to acquire the binding energy of specific elements and valence band spectra (0–20 eV). In addition, the C 1s spectrum is separated into three peaks centered at (1) ∼284.8 eV, representing the CC bond, (2) ∼285.5 eV, representing the CO bond, and (3) ∼288.5 eV, representing the OCO bond . Then, all data are calibrated by referencing the peak location of the CC bond, and each core level (CL) spectrum is fitted using Lorentzian–Gaussian line shapes by employing a Shirley background subtraction.…”