Pulsed heating atomic layer deposition (PH-ALD) for epitaxial growth of zinc oxide thin films on c-plane sapphire. Issue 1 (13th December 2021)

• Record Type: Journal Article
• Authors: Piercy, Brandon D.; Wooding, Jamie P.; Gregory, Shawn A.; Losego, Mark D.
• Is Part Of: Dalton transactions. Volume 51:Issue 1(2021)
• Page Start: 303
• Page End: 311
• Publication Date: 2021-12-13
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/d1dt03581a
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : High-temperature heat pulses interleaved with ALD cycling enables the growth of heteroepitaxial ZnO on c -plane sapphire substrates. This "pulsed-heating" ALD separates the chemistry delivery process from the material's structural crystallization. Abstract : An in situ pulsed heating atomic layer deposition (PH-ALD) technique is used to grow heteroepitaxial ZnO thin films on c -plane sapphire with temperature-sensitive metalorganic precursors. During metalorganic precursor delivery, the substrate is maintained at a base temperature of 110 °C to prevent thermal decomposition of the precursors. After the substrate is sequentially exposed to the metalorganic precursor and water co-reactant at this low temperature, a high-power resistive heater is used to rapidly heat the substrate to between 400 and 900 °C to drive film crystallization. These in situ heat pulses enable epitaxial growth of (0001) ZnO films on c -plane sapphire. Rocking curves with FWHM of values as low as 0.53° are achieved. In contrast, films deposited entirely at 110 °C appear random polycrystalline and post-deposition annealing to 900 °C achieves only partial "epitaxial character" with a notably different in-plane orientation. Variations in heat pulse temperature and the number of deposition cycles between heat pulses are explored. Epitaxial growth persists up to 5 deposition cycles per heat pulse, with the 2 θ – ω FWHM increasing to 1–2°. To further reduce process times, a templating approach is also explored in which a limited number of "template" layers are initially deposited with PH-ALD followed by low-temperature ALD at 110 °C. Epitaxial growth is encouraged with as few as 5 cycles of PH-ALD followed by 495 cycles of low-temperature ALD. Crystal quality further improves by using up to 50 template cycles, with a 2 θ – ω FWHM of 1.3°. Epilayers also show enhanced photoluminescence (PL) at room temperature. These results demonstrate how in situ pulse-heating can be used to promote epitaxial film growth in ALD processes using temperature-sensitive metalorganic precursors.