@article{xue_palmese_sekely_little_kish_muth_wierer_2024, title={Growth and characterization of AlInN/GaN superlattices}, volume={630}, ISSN={["1873-5002"]}, url={https://doi.org/10.1016/j.jcrysgro.2024.127567}, DOI={10.1016/j.jcrysgro.2024.127567}, abstractNote={Data are presented on near-lattice-matched Al1-xInxN/GaN superlattices (SLs) with superior morphology to thick AlInN layers. The SLs are grown by metalorganic chemical vapor deposition and consist of ∼3 nm thick AlInN, ∼1 nm thick GaN layers, and x=0.153 to 0.203. The SLs are grown with either 20 or 100 periods on GaN-on-sapphire or free-standing GaN substrates. Growth conditions are explored, and the In-content of the AlInN layers within the SL increases with growth temperature and pressure, while the growth rate decreases with pressure. Thick AlInN layers grown on GaN-on-sapphire exhibit island growth with a root mean square (rms) roughness of ∼0.65 nm, while the AlInN/GaN SLs have steplike morphology and rms ∼0.3 nm. Also, 80 nm thick AlInN/GaN SLs grown on GaN substrates exhibit nearly perfect steplike morphology with a lower rms of ∼0.13 nm and extremely low pit densities. The refractive index of the SLs is the weighted average of AlInN and GaN, and they emit light from the quantum states within the thin GaN layers. These AlInN/GaN SLs are a potential replacement for AlInN layers in optoelectronic and electronic devices that require steplike morphology and controlled pitting.}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Xue, Haotian and Palmese, Elia and Sekely, Ben J. and Little, Brian D. and Kish, Fred A. and Muth, John F. and Wierer, Jonathan J.}, year={2024}, month={Mar} }
 @article{palmese_xue_pavlidis_wierer_2023, title={Enhancement-Mode AlInN/GaN High-Electron-Mobility Transistors Enabled by Thermally Oxidized Gates}, volume={12}, ISSN={["1557-9646"]}, url={https://doi.org/10.1109/TED.2023.3343313}, DOI={10.1109/TED.2023.3343313}, abstractNote={Enhancement mode AlInN/gallium nitride (GaN) high-electron-mobility transistors (HEMTs) are fabricated by thermally oxidizing the barrier region under the gate. The oxidation is performed at 850 °C in <inline-formula> <tex-math notation="LaTeX">$\text{O}_{{2}}$ </tex-math></inline-formula>, and a SiNx mask is used to achieve selective oxidization of the AlInN layer. For comparison, a standard Schottky gate and atomic layer deposition (ALD) Al2O3 metal–insulator–semiconductor (MIS) HEMTs are fabricated from the same structure and show depletion mode behavior as expected. Scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS) mappings are performed to characterize the gate of the oxidized HEMTs, showing complete oxidation of the AlInN barrier. All the devices are tested to determine their transfer and output characteristics. The results show that the thermally oxidized gate produces a positive shift in threshold voltage at ~4 V and low currents (<inline-formula> <tex-math notation="LaTeX">$\sim 2\times 10^{-{7}}$ </tex-math></inline-formula> mA/mm) at zero gate voltage. The oxidized HEMTs are also subjected to postmetallization annealing (PMA) at 400 °C and 500 °C for 10 min flowing 1000 sccm of <inline-formula> <tex-math notation="LaTeX">$\text{N}_{{2}}$ </tex-math></inline-formula>, retaining enhancement mode behavior and leading to a further positive shift in threshold voltage.}, journal={IEEE TRANSACTIONS ON ELECTRON DEVICES}, author={Palmese, Elia and Xue, Haotian and Pavlidis, Spyridon and Wierer, Jonathan J.}, year={2023}, month={Dec} }
 @article{xue_palmese_song_chowdhury_strandwitz_wierer jr_2023, title={Structural and optical characterization of thin AlInN films on c-plane GaN substrates}, volume={134}, ISSN={["1089-7550"]}, url={https://doi.org/10.1063/5.0136004}, DOI={10.1063/5.0136004}, abstractNote={The structure and optical characteristics of thin (∼30 nm) wurtzite AlInN films grown pseudomorphic on free-standing, c-plane GaN substrates are presented. The Al1−xInxN layers are grown by metalorganic chemical vapor deposition, resulting in films with varying In content from x = 0.142 to 0.225. They are measured using atomic force microscopy, x-ray diffraction, reciprocal space mapping, and spectroscopic ellipsometry (SE). The pseudomorphic AlInN layers provide a set where optical properties can be determined without additional variability caused by lattice relaxation, a crucial need for designing devices. They have smooth surfaces (rms < 0.29 nm) with minimum pit areas when the In content is near lattice-matched to GaN. As expected, SE shows that the refractive index increases and the bandgap energy decreases with increased In-content. Plots of bandgap energy vs In content are fitted with a single bowing parameter of 3.19 eV when using bandgap energies for AlN and InN pseudomorphic to GaN, which is lower than previous measurements and closer to theoretical predictions.}, number={7}, journal={JOURNAL OF APPLIED PHYSICS}, author={Xue, Haotian and Palmese, Elia and Song, Renbo and Chowdhury, Md Istiaque and Strandwitz, Nicholas C. and Wierer Jr, Jonathan J.}, year={2023}, month={Aug} }