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Growth of wurtzite Sc x Al 1−x N (x < 0.23) by plasma-assisted molecular-beam epitaxy on c-plane GaN at high temperatures significantly alters the extracted lattice constants of the material due to defects likely associated with remnant phases. In contrast, ScAlN grown below a composition-dependent threshold temperature exhibits uniform alloy distribution, reduced defect density, and atomic-step surface morphology. The c-plane lattice constant of this low-temperature ScAlN varies with composition as expected from previous theoretical calculations and can be used to reliably estimate alloy composition. Moreover, lattice-matched Sc 0.18 Al 0.82 N/GaN multi-quantum wells grown under these conditions display strong and narrow near-infrared intersubband absorption lines that confirm advantageous optical and electronic properties.
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Enhanced near-infrared absorption in lattice-matched Sc 0.14 Al 0.86 N/GaN multi-quantum wells: growth optimization and insights into polarization parameters
We report on the near-infrared intersubband (ISB) absorption properties of strain-free Sc0.14Al0.86N/GaN multiple quantum wells (MQWs) grown on c-plane GaN substrates by molecular beam epitaxy. These MQWs exhibit strong, sharp, and tunable absorption energies between 515 meV and 709 meV, for well widths ranging from 7 nm to 1.5 nm, respectively. Observation of ISB absorption in ultra-thin Sc0.14Al0.86N/GaN MQWs not only extends the near-infrared range accessible with Sc-containing nitrides but also highlights the challenges of growing nanometer-thick GaN quantum wells. We explore the effects of growth temperature on absorption characteristics and find that substrate temperatures above 600°C significantly enhance ISB absorption intensity but also introduce an energy redshift for the narrowest wells. The redshift is attributed to increased interface roughness due to ScAlN surface morphology degradation at higher temperatures. Additionally, a comparison of experimental results with simulated band-structures indicates that the magnitude of net polarization rises faster with Sc-composition than previously suggested by theoretical calculations. This study advances the prospects of ScAlN/GaN heterostructures for novel photonic devices in the technologically important near-infrared range.
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- Award ID(s):
- 2414283
- PAR ID:
- 10565118
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Optical Materials Express
- Volume:
- 15
- Issue:
- 2
- ISSN:
- 2159-3930
- Format(s):
- Medium: X Size: Article No. 164
- Size(s):
- Article No. 164
- Sponsoring Org:
- National Science Foundation
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