Metalorganic chemical vapor phase deposition of AlScN/GaN heterostructures

Abstract

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 to 2 × 1013 cm−2 and close to 900 cm2/(V s), respectively, resulted in channel sheet resistances as low as 337 Ω/sq, very suitable for AlScN/GaN HEMTs. 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.

Effect of AlN and AlGaN Interlayers on AlScN/GaN Heterostructures Grown by Metal–Organic Chemical Vapor Deposition

“…The barrier and interlayer thicknesses measured by HRXRD increased with the temperature from 9.5 nm at 900 °C to 15.4 nm at 1200 °C (samples D2 and F2 grown on Al 2 O 3 , Table 1). The higher the deposition temperature, the more Sc gets incorporated into the layer, 22 even though the Sc flow was adjusted accordingly. We measured a Sc content of 1.4% in the sample grown at 900 °C and 9.0% in the one grown at 1200 °C.…”

“…19 We demonstrated that the growth of AlScN by MOCVD is possible by employing a proprietary heating and gas mixing system which is tailored to the useage of Cp 3 Sc. 21 The effects of growth parameters such as temperature, growth mode, V/III ratio, and pressure were investigated, 22 as well as the diffusion behavior of Al-, Sc-, and Ga-atoms and the influence of GaN and SiN x cap layers on the oxidation of the underlying barrier. 23 SiN x was found to be the ideal passivation layer to prevent oxidation of the AlScN barrier while GaN tends to grow in a 3D-mode on Sc-rich layers.…”

“…We demonstrated that the growth of AlScN by MOCVD is possible by employing a proprietary heating and gas mixing system which is tailored to the useage of Cp 3 Sc . The effects of growth parameters such as temperature, growth mode, V/III ratio, and pressure were investigated, as well as the diffusion behavior of Al-, Sc-, and Ga-atoms and the influence of GaN and SiN x cap layers on the oxidation of the underlying barrier . SiN x was found to be the ideal passivation layer to prevent oxidation of the AlScN barrier while GaN tends to grow in a 3D-mode on Sc-rich layers. , SiN x passivation is also expected to improve the device performance by the reduction of dispersion, which was recently demonstrated by Tahhan et al Meanwhile, we achieved the first promising results using the novel precursor (MCp) 2 ScCl with increased vapor pressure which are discussed in detail in Streicher et al .…”

Vertical and Lateral Etch Survey of Ferroelectric AlN/Al1−xScxN in Aqueous KOH Solutions

“…Single-crystal Al 1−x Sc x N can be grown by molecular beam epitaxy (MBE) [ 9 ] on 100 mm wafers [ 37 ] with scandium concentration x from 0.06 to 0.36 [ 38 ]. The growth of Sc alloyed AlN via metal–organic chemical vapor deposition (MOCVD) had suffered from the lack of Sc precursors [ 39 ]; however, research in this field is catching up quickly, and the ability to grow 36% Sc alloyed Al 1−x Sc x N films on 100 mm wafers has been demonstrated [ 40 , 41 ]. High-quality polycrystalline Al 1−x Sc x N films can be deposited with physical vapor deposition (PVD) methods such as magnetron sputtering.…”

Band Alignment of ScxAl1–xN/GaN Heterojunctions

“…The epitaxial integration of wurtzite ScAlN on GaN was demonstrated recently with molecular beam epitaxy (MBE) − and metal–organic chemical vapor deposition, , indicating the ability to produce a higher quality thin film material when compared with traditional sputtering techniques. One key area to exploit the high inherent polarization of ScAlN is in the design of next-generation III–N HEMTs, where ScAlN has been used as a barrier layer to increase channel charge densities by a factor of 5 higher than AlGaN-barrier GaN HEMTs. ,, …”