MOCVD Growth and Characterization of ZnSnN₂

Conference · Wed Jun 24 00:00:00 EDT 2020

DOI:https://doi.org/10.2172/1677510· OSTI ID:1677510

Jayatunga, Benthara Hewage Dinushi; Karim, Md Rezaul; Zhu, Menglin; Hwang, Jinwoo; Zhao, Hongping; Kash, Kathleen

Since the first few reports of its synthesis in 2011 and 20121-3, interest in ZnSnN₂ for diverse applications, including photovoltaics1,3,4, visible light photocatalysis5, and optoelectronics, has been growing. Novel nitride-based LED device designs promise high gains in efficiency at emission wavelengths into the green, amber and even red.6-8 Their realization requires the precise insertion of an ultrathin layer of ZnGeN₂ or ZnSnN₂ into the active region of an InGaAs-GaAs LED structure. While thin films of ZnSnN₂ have been synthesized by RF sputtering1,9 and by MBE 2,10,11, and thin films of ZnGeN₂, ZnSiN₂ and their alloys by MOCVD, the synthesis of ZnSnN₂ thin films by MOCVD has not yet been reported. It is a challenging goal, given the narrow temperature window between efficient activation of ammonia and the thermal decomposition of ZnSnN₂ at near-atmospheric pressures. We report here the results of studies of ZnSnN₂ films grown on r- and c-plane sapphire substrates, GaN templates on sapphire, and In_0.15Ga_0.85N templates on GaN-on-sapphire, at temperatures from 500 °C to 560 °C, using tetramethyltin (TMSn), diethylzinc (DEZn), germane and ammonia. Chamber pressures were varied between 200 and 500 torr. In addition, the ratios of the cation precursors and the total cation-to-anion precursor ratios were varied. Single crystal growth, as evidenced by 2θ-ω x-ray diffraction scans, was achieved on all of these substrates. Wurtzitic (0002) ZnSnN₂ diffraction were observed at 2θ ~ 32.90 for the samples grown on c-sapphire, GaN (0001) and InGaN (0001) templates, and wurtzitic (11-20) peak at 2θ ~ 54.80 for the films grown on r-sapphire. Higher pressures and higher temperatures promoted better crystallinity and more continuous films, as revealed by scanning electron microscopy (SEM) images and 2θ-ω x-ray diffraction peak widths and intensities. Crystal quality was observed to be highly dependent on growth temperature. For example, in one series a 10 °C change in growth temperature resulting in a factor of 15 increase in diffraction peak intensity. SEM images show that films grown on the GaN templates had better uniformity in nucleation than those grown on sapphire. The presence of satellite peaks around the Bragg peak in the XRD 2θ-ω scan for a film grown on a GaN template, and the absence of satellite peaks for the films grown simultaneously on c- and r-sapphire, also indicate superior quality for the film grown on GaN. HAADF-STEM images of films grown on these templates showed smooth interfaces at the film-substrate boundary and show growth rates as high as 167 nm/h, considerably higher than reported previously for MBE growth.9,10 Electron diffraction patterns show single crystallinity. Rocking curves show FWHM as low as 0.100. RMS surfaces roughnesses, measured by atomic force microscopy, are of the order of 3 nm for 1µm x 1µm areas. Current work is focusing on optimizing growth on InGaN templates. These templates are promising for their relatively lower lattice mismatch with ZnSnN₂. Their use is a next step toward producing LED device structures.

• Research Organization: The Ohio State University, Case Western Reserve University
• Sponsoring Organization: USDOE Office of Energy Efficiency and Renewable Energy (EERE)
• DOE Contract Number: EE0008718
• OSTI ID: 1677510
• Resource Relation: Conference: 62nd Electronic Materials Conference June 24-26, 2020 Virtual
• Country of Publication: United States
• Language: English