Title: Synthesis and Calculations of Wurtzite Al _{1– x} Gd _x N Heterostructural Alloys

Abstract

Al1-xGdxN is one of a series of novel heterostructural alloys involving rare earth cations with potentially interesting properties for (opto)electronic, magnetic, and neutron detector applications. Using alloy models in conjunction with density functional theory, we explored the full composition range for Al1-xGdxN and found that wurtzite is the ground-state structure up to a critical composition of xc = 0.82. The calculated temperature-composition phase diagram reveals a large miscibility gap inducing spinodal decomposition at equilibrium conditions, with higher Gd substitution (meta)stabilized at higher temperatures. By depositing combinatorial thin films at high effective temperatures using radio-frequency cosputtering, we have achieved the highest Gd3+ incorporation into the wurtzite phase reported to date, with single-phase compositions at least up to x equals approximately 0.25 confirmed by high-resolution synchrotron grazing incidence wide-angle X-ray scattering. High-resolution transmission electron microscopy on material with x equals approximately 0.13 and x equals approximately 0.24 confirmed a uniform composition polycrystalline film with uniform columnar grains having the wurtzite structure. Spectroscopic ellipsometry and cathodoluminescence spectroscopy measurements are employed to probe the optoelectronic properties, showing that the band gap decreases with increasing Gd content x and that this effect causes the ideal Gd substitution level for cathodoluminescence applications to be low. Expandingmore » our calculations to other rare earth cations (Pr3+ and Tb3+) reveals similar thermodynamic stability and solubility behavior to Gd. From this and previous studies on Al1-xScxN, we elucidate that both smaller ionic radius and higher bond ionicity promote increased incorporation of group IIIB cations into wurtzite AlN. This work furthers the development of design rules for new alloys in this material family.« less

Authors:

Smaha, Rebecca W.  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-8349-2615"

Yazawa, Keisuke ^[1]; Norman, Andrew G.  ^[1];

• Search DOE PAGES for author "Norman, Andrew G."
• Search DOE PAGES for ORCID "0000-0001-6368-521X"

Mangum, John S.  ^[1];

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Guthrey, Harvey  ^[1];

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Brennecka, Geoff L.  ^[2];

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• Search DOE PAGES for ORCID "0000-0002-4476-7655"

Zakutayev, Andriy  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-3054-5525"

Bauers, Sage R.  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-6505-5016"

Gorai, Prashun ^[3]; Haegel, Nancy M. ^[1]

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+ Show Author Affiliations

1. National Renewable Energy Lab, Golden, Colorado80401, United States
2. Colorado School of Mines, Golden, Colorado80401, United States
3. National Renewable Energy Lab, Golden, Colorado80401, United States, Colorado School of Mines, Golden, Colorado80401, United States

Publication Date:

Mon Nov 21 00:00:00 EST 2022

Research Org.:

National Renewable Energy Lab. (NREL), Golden, CO (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES); USDOE Office of Energy Efficiency and Renewable Energy (EERE); USDOE Office of Science (SC), Advanced Scientific Computing Research (ASCR)

OSTI Identifier:

1899206

Alternate Identifier(s):

OSTI ID: 1903501; OSTI ID: 1960761

Report Number(s):

NREL/JA-5K00-84555
Journal ID: ISSN 0897-4756

Grant/Contract Number:  

AC36-08GO28308; AC02-76SF00515

Resource Type:

Published Article

Journal Name:

Chemistry of Materials

Additional Journal Information:

Journal Name: Chemistry of Materials Journal Volume: 34 Journal Issue: 23; Journal ID: ISSN 0897-4756

Publisher:

American Chemical Society

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; first-principles calculations; heterostructural alloys; scattering; sputtering; TEM; wurtzite; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY