Trigonal tellurium (Te) is a chiral semiconductor that lacks both mirror and inversion symmetries, resulting in complex band structures with Weyl crossings and unique spin textures. Detailed time-resolved polarized reflectance spectroscopy is used to investigate its band structure and carrier dynamics. The polarized transient spectra reveal optical transitions between the uppermost spin-split
Palladium (Pd) electrodes have enabled superior performance in Te‐based devices. Theory predicts strong Fermi level (EF) pinning near the Te valence band, which likely explains the predominant
- NSF-PAR ID:
- 10452178
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Materials Interfaces
- Volume:
- 8
- Issue:
- 7
- ISSN:
- 2196-7350
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract H 4andH 5and the degenerateH 6valence bands (VB) and the lowest degenerateH 6conduction band (CB) as well as a higher energy transition at the L-point. Surprisingly, the degeneracy of theH 6CB (a proposed Weyl node) is lifted and the spin-split VB gap is reduced upon photoexcitation before relaxing to equilibrium as the carriers decay. Using ab initio density functional theory (DFT) calculations, we conclude that the dynamic band structure is caused by a photoinduced shear strain in the Te film that breaks the screw symmetry of the crystal. The band-edge anisotropy is also reflected in the hot carrier decay rate, which is a factor of two slower along thec -axis than perpendicular to it. The majority of photoexcited carriers near the band-edge are seen to recombine within 30 ps while higher lying transitions observed near 1.2 eV appear to have substantially longer lifetimes, potentially due to contributions of intervalley processes in the recombination rate. These new findings shed light on the strong correlation between photoinduced carriers and electronic structure in anisotropic crystals, which opens a potential pathway for designing novel Te-based devices that take advantage of the topological structures as well as strong spin-related properties. -
more » « less
Abstract Under varying growth and device processing conditions, ultrabroadband photoconduction (UBPC) reveals strongly evolving trends in the defect density of states (DoS) for amorphous oxide semiconductor thin‐film transistors (TFTs). Spanning the wide bandgap of amorphous InGaZnO
x (a‐IGZO), UBPC identifies seven oxygen deep donor vacancy peaks that are independently confirmed by energetically matching to photoluminescence emission peaks. The subgap DoS from 15 different types of a‐IGZO TFTs all yield similar DoS, except only back‐channel etch TFTs can have a deep acceptor peak seen at 2.2 eV below the conduction band mobility edge. This deep acceptor is likely a zinc vacancy, evidenced by trap density which becomes 5‐6× larger when TFT wet‐etch methods are employed. Certain DoS peaks are strongly enhanced for TFTs with active channel processing damage caused from plasma exposure. While Ar implantation and He plasma processing damage are similar, Ar plasma yields more disorder showing a ≈2 × larger valence‐band Urbach energy, and two orders of magnitude increase in the deep oxygen vacancy trap density. Changing the growth conditions of a‐IGZO also impacts the DoS, with zinc‐rich TFTs showing much poorer electrical performance compared to 1:1:1 molar ratio a‐IGZO TFTs owing to the former having a ∼10 × larger oxygen vacancy trap density. Finally, hydrogen is found to behave as a donor in amorphous indium tin gallium zinc oxide TFTs. -
more » « less
It has been challenging to synthesize p-type SnOx(1≤x<2) and engineer the electrical properties such as carrier density and mobility due to the narrow processing window and the localized oxygen 2p orbitals near the valence band.
We recently reported on the processing of p-type SnOx and an oxide-based p-n heterostructures, demonstrating high on/off rectification ratio (>103), small turn-on voltage (<0.5 V), and low saturation current (~1×10-10A)1. In order to further understand the p-type oxide and engineer the properties for various electronic device applications, it is important to identify (or establish) the dominating doping and transport mechanisms. The low dopability in p-type SnOx, of which the causation is also closely related to the narrow processing window, needs to be mitigated so that the electrical properties of the material are to be adequately engineered2, 3.
Herein, we report on the multifunctional encapsulation of p-SnOxto limit the surface adsorption of oxygen and selectively permeate hydrogen into the p-SnOxchannel for thin film transistor (TFT) applications. Time-of-flight secondary ion mass spectrometry measurements identified that ultra-thin SiO2as a multifunctional encapsulation layer effectively suppressed the oxygen adsorption on the back channel surface of p-SnOxand augmented hydrogen density across the entire thickness of the channel. Encapsulated p-SnOx-based TFTs demonstrated much-enhanced channel conductance modulation in response to the gate bias applied, featuring higher on-state current and lower off-state current. The relevance between the TFT performance and the effects of oxygen suppression and hydrogen permeation is discussed in regard to the intrinsic and extrinsic doping mechanisms. These results are supported by density-functional-theory calculations.
Acknowledgement This work was supported by the U.S. National Science Foundation (NSF) Award No. ECCS-1931088. S.L. and H.W.S. acknowledge the support from the Improvement of Measurement Standards and Technology for Mechanical Metrology (Grant No. 20011028) by KRISS. K.N. was supported by Basic Science Research Program (NRF-2021R11A1A01051246) through the NRF Korea funded by the Ministry of Education.
References Lee, D. H.; Park, H.; Clevenger, M.; Kim, H.; Kim, C. S.; Liu, M.; Kim, G.; Song, H. W.; No, K.; Kim, S. Y.; Ko, D.-K.; Lucietto, A.; Park, H.; Lee, S., High-Performance Oxide-Based p–n Heterojunctions Integrating p-SnOx and n-InGaZnO.
ACS Applied Materials & Interfaces 2021, 13 (46), 55676-55686.Hautier, G.; Miglio, A.; Ceder, G.; Rignanese, G.-M.; Gonze, X., Identification and design principles of low hole effective mass p-type transparent conducting oxides.
Nat Commun 2013, 4 .Yim, K.; Youn, Y.; Lee, M.; Yoo, D.; Lee, J.; Cho, S. H.; Han, S., Computational discovery of p-type transparent oxide semiconductors using hydrogen descriptor.
npj Computational Materials 2018, 4 (1), 17.Figure 1
-
X-ray photoemission spectroscopy (XPS) has been used to examine the interaction between Au and HfS 3 at the Au/HfS 3 interface. XPS measurements reveal dissociative chemisorption of O 2 , leading to the formation of an oxide of Hf at the surface of HfS 3 . This surface hafnium oxide, along with the weakly chemisorbed molecular species, such as O 2 and H 2 O, are likely responsible for the observed p-type characteristics of HfS 3 reported elsewhere. HfS 3 devices exhibit n-type behaviour if measured in vacuum but turn p-type in air. Au thickness-dependent XPS measurements provide clear evidence of band bending as the S 2p and Hf 4f core-level peak binding energies for Au/HfS 3 are found to be shifted to higher binding energies. This band bending implies formation of a Schottky-barrier at the Au/HfS 3 interface, which explains the low measured charge carrier mobilities of HfS 3 -based devices. The transistor measurements presented herein also indicate the existence of a Schottky barrier, consistent with the XPS core-level binding energy shifts, and show that the bulk of HfS 3 is n-type.more » « less
-
more » « less
Abstract Films of n-GaAs1-xBixfilms were grown via molecular beam epitaxy using both Si and Te as dopant sources. Electron mobility was characterized by Hall effect measurements as a function of carrier concentration and Bi content for films with bismuth fractions of x = 0.02 and x = 0.06. While GaAsBi:Te shows lower majority carrier mobility than GaAsBi:Si at low Bi concentrations, the two become comparable as Bi content increases. Furthermore, it was observed that in the presence of bi-metallic Bi-Ga droplets on the film surface, films doped with Si display p-type behavior, likely due to Si preferentially occupying group-V sites. The use of Te as a dopant always resulted in n-type epilayers, making it a more reliable dopant choice for high Bi content films. Finally,
ex situ annealing was studied as a method to improve majority carrier mobility in GaAs0.98Bi0.02:Te films, with a 10 min anneal at 350 °C resulting in a 30% improvement in electron mobility. Improvement of film quality was confirmed through spectroscopic ellipsometry examination of film optical properties. Annealing at higher temperatures resulted in electrical, optical, and structural degradation of the GaAsBi films.
