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Metalorganic chemical vapor phase deposition of AlScN/GaN heterostructures

: Ligl, Jana; Leone, Stefano; Manz, Christian; Kirste, Lutz; Doering, Philipp; Fuchs, Theodor; Prescher, Mario; Ambacher, Oliver


Journal of applied physics 127 (2020), Nr.19, Art. 195704, 9 S.
ISSN: 0021-8979
ISSN: 1089-7550
Fraunhofer IAF ()

AlScN/GaN heterostructures are worth investigating due to the remarkable high gradients in spontaneous polarization at their interfaces, which brings them into play for a wide field of potential high-power and high-frequency electronic applications. In this work, AlScN/GaN heterostructures for high electron mobility transistor (HEMT) structures were grown by metalorganic chemical vapor deposition. We have investigated the impact of growth parameters on thick AlScN layers and on thin AlScN/GaN heterostructures. Growth parameters, such as temperature, V/III ratio, pressure, and growth mode, were varied with the focus on surface morphology, crystal quality, and incorporation of impurities. High growth temperatures improve the surface quality and reduce impurities incorporation notably. In addition to that, a slight decrease in carbon concentration is obtained by adopting a pulsed supply of metalorganic precursors. V/III ratio and pressure did not influence the layer quality observably. Heterostructures with root mean square surface roughness values as low as 0.38 nm, revealing smooth growth steps, were achieved. The presence of two-dimensional electron gases with sheet carrier densities and mobilities of up to2 × 1013cm−2 and close to 900 cm2/(V s), respectively, resulted in channel sheet resistances as low as 337 Ω/sq, very suitable for AlScN/GaNHEMTs. Heterostructures with sheet resistances below 200 Ω/sq and sheet carrier densities of 5 × 10¹³ cm⁻ ² were also achieved but showed significantly lower mobility.