Attention:The NSF Public Access Repository (PAR) system and access will be unavailable from 5:00 PM ET until 8:00 PM ET on Friday, September 11 due to maintenance. We apologize for the inconvenience.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Oxygen impurities in AlN and their impact on optical absorption
Oxygen is a common impurity in AlN samples. Using hybrid density functional calculations, we investigate the role of substitutional oxygen (ON) in the optical absorption. We construct configuration coordination diagrams for ON and related complexes. Our results indicate that an optical transition involving ON− (a DX center) gives rise to an absorption band peaked at 2.22 eV, suggesting it is a source of the absorption band with an onset at ∼ 2 eV observed in oxygen-containing samples. We also propose that neutral ON–DX complexes can form, which would give rise to absorption peaking at 3.06 eV. In addition, we find that oxygen, in spite of its DX character, may behave as an “optically shallow donor” and be involved in optical transitions from deep defect states to the conduction band. This observation provides an alternative physical mechanism for the optical absorption bands observed in AlN samples in the visible and ultraviolet (UV) region.  more » « less
Award ID(s):
2314050
PAR ID:
10594510
Author(s) / Creator(s):
; ; ; ;
Publisher / Repository:
AIP publishing
Date Published:
Journal Name:
Applied Physics Letters
Volume:
126
Issue:
6
ISSN:
0003-6951
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; ; ; (, Journal of Applied Physics)
    GaN samples were implanted with Be and annealed in different conditions in order to activate the shallow Be Ga acceptor. Low-temperature photoluminescence spectra were studied to find Be Ga -related defects in the implanted samples. A yellow band with a maximum at about 2.2 eV (the YL Be band) was observed in nearly all samples protected with an AlN cap during the annealing and in samples annealed under ultrahigh N 2 pressure. A green band with a maximum at 2.35 eV (the GL2 band), attributed to the nitrogen vacancy, was the dominant defect-related luminescence band in GaN samples annealed without a protective AlN layer. The ultraviolet luminescence (UVL Be ) band with a maximum at 3.38 eV attributed to the shallow Be Ga acceptor with the ionization energy of 0.113 eV appeared in implanted samples only after annealing at high temperatures and ultrahigh N 2 pressure. This is the first observation of the UVL Be band in Be-implanted GaN, indicating successful activation of the Be Ga acceptor. 
    more » « less
  2. ; ; ; ; ; (, Applied Physics Letters)
    State-of-the-art semiconducting aluminum nitride (AlN) films were characterized by cathodoluminescence (CL) spectroscopy in the range of 200–500 nm in an attempt to identify the energy levels within the bandgap and their associated defects. Near-band edge emission (around 206 nm) and high-intensity peaks centered in the near UV range (around 325 nm) are observed for both n- and p-type AlN films. The near UV peaks are potentially associated with oxygen contamination in the films. The p-type AlN films contain at least two unidentified peaks above 400 nm. Assuming that the dopant concentration is independent of compensation (i.e., in the perfect doping limit), three effective donor states are found from Fermi–Dirac statistics for Si-doped AlN, at ∼0.035, ∼0.05, and ∼0.11 eV. Similarly, a single effective acceptor energy of ∼0.03–0.05 eV (depending on the degeneracy factory considered) was found for Be doped AlN. CL investigation of doped AlN films supports claims that AlN may be a promising optoelectronic material, but also points to contaminant mitigation and defect theory as major areas for future study. 
    more » « less
  3. ; ; ; ; ; (, Applied Physics Letters)
    Magnesium (Mg) doped, copper (Cu) doped, and Mg and Cu co-doped β-Ga2O3 thin film samples were grown on c-plane sapphire substrates using plasma-assisted molecular beam epitaxy. X-ray photoelectron spectroscopy analysis confirmed the doping concentrations. In addition, changes in the valence band density of states near the valence band maximum were revealed, while no Fermi-level shifts were observed in all doped samples, suggesting no electrical conductivity change compared to the undoped sample. Room-temperature photoluminescence (PL) characterization using an ArF laser of 193 nm excitation and subsequent PL peak deconvolution were performed. No near-band edge emissions were observed. The PL in each sample is dominated by optical transitions between the conduction band and self-trapped hole levels, and donor–acceptor pair transitions. These donors and acceptors originate from oxygen vacancies (VO) and gallium–oxygen vacancy complexes (VGa–VO), respectively. No visible transitions assignable to Mg and Cu acceptor levels could be extracted. 
    more » « less
  4. ; ; (, Journal of Materials Chemistry C)
    null (Ed.)
    Orthorhombic BaZrS 3 is a potential optoelectronic material with prospective applications in photovoltaic and thermoelectric devices. While efforts exist on understanding the effects of elemental substitution and material stability, fundamental knowledge on the electronic transport properties are sparse. We employ first principles calculations to examine the electronic band structure and optical band gap and interrogate the effect of electron transport on electrical and thermal conductivities, and Seebeck coefficient, as a function of temperature and chemical potential. Our results reveal that BaZrS 3 has a band gap of 1.79 eV in proximity of the optimal 1.35 eV recommended for single junction photovoltaics. An absorption coefficient of 3 × 10 5 cm −1 at photon energies of 3 eV is coupled with an early onset to optical absorption at 0.5 eV, significantly below the optical band gap. The carrier effective mass being lower for electrons than holes, we find the Seebeck coefficient to be higher for holes than electrons. A notable (≈1.0 at 300 K) upper limit to the thermoelectric figure of merit, obtained due to high Seebeck coefficient (3000 μV K −1 ) and ultra-low electron thermal conductivity, builds promise for BaZrS 3 as a thermoelectric. 
    more » « less
  5. ; (, Journal of Applied Physics)
    Annealed bulk crystals of barium titanate (BaTiO 3 ) exhibit persistent photoconductivity (PPC) at room temperature. Samples were annealed in a flowing gas of humid argon and hydrogen, with a higher flow rate corresponding to larger PPC. When exposed to sub-bandgap light, a broad infrared (IR) absorption peak appears at 5000 cm −1 (2  μm), attributed to polaronic or free-carrier absorption from electrons in the conduction band. Along with the increased IR absorption, electrical resistance is reduced by a factor of approximately two. The threshold photon energy for PPC is 2.9 eV, similar to the case of SrTiO 3 . This similarity suggests that the mechanisms are similar: an electron in substitutional hydrogen (H O ) is photoexcited into the conduction band, causing the proton to leave the oxygen vacancy and attach to a host oxygen atom. The barrier to recover to the ground state is large such that PPC persists at room temperature. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Text Encoded Conversion
  • XML
  • Save / Share this Record
  • Send to Email