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

Abstract

AlScN/GaN heterostructures with their high sheet carrier density (n s ) in the two-dimensional electron gas (2DEG) have a high potential for high-frequency and high-power electronics. The abruptness of the heterointerface plays a key role in the 2DEG confinement, and the presence of interlayers (AlN, AlGaN) affects n s and electron mobility (μ) and determines the sheet resistance (R sh ). AlScN/GaN heterostructures suitable for high-electron mobility transistors (HEMT) with and without a nominal AlN interlayer were grown by metal−organic chemical vapor deposition (MOCVD) and characterized electrically and structurally to gain a systematic insight into the unintentional formation and control of graded AlGaN interlayers by diffusion of atoms at the heterointerface. The AlN interlayer increases n s from 2.52 × 10 13 cm −2 to 3.25 × 10 13 cm −2 and, as calculated by one-dimensional Schrodinger−Poisson simulations, improves the 2DEG confinement. The barrier growth temperature was varied from 900 °C to 1200 °C to investigate the effect of the thermal budget on diffusion. Growth at 900 °C reduces the thickness of the graded AlGaN interlayer and improves the 2DEG confinement, leading to R sh of 211 Ω/sq, n s of 2.98 × 10 13 cm −2 , and μ of 998 cm 2 /(Vs).

Metal‐Organic Chemical Vapor Deposition of Aluminum Yttrium Nitride

“…[44,48] We demonstrated that a slight modification of the gas mixing system in a commercial MOCVD setup [49,50] could enable the growth of AlScN by MOCVD with standard commercially available cyclopentadienyl-based Sc precursors by heating the source to 150 °C. [45,[51][52][53] We have recently reported that new precursors are under development [54] and feature a higher vapor pressure. However, the only attempt to grow Y-containing nitrides by MOCVD relied on using cyclopentadienyl-based Y precursors (MeCp) 3 Y and (t-BuCp) 3 Y, with the last one enabling doping levels of Y incorporated in GaN (5.3 Â 10 18 cm À3 ).…”

Enhanced AlScN/GaN Heterostructures Grown with a Novel Precursor by Metal–Organic Chemical Vapor Deposition

“…Contactless Hall measurements on AlScN HEMT structures grown on 4 H‐SiC wafers with (red circles) at different temperatures. The values achieved with (blue triangles) [ 21 ] are shown for comparison. a) Sheet resistance , b) sheet charge carrier density , and c) electron mobility μ are average values obtained for the 100 mm wafers.…”

“…The electrical performance of AlScN HEMT structures grown with the novel precursor (red squares) is compared to the results obtained with (green triangles), [ 21 ] and our previously published results (black symbols), [ 17,18 ] as well as to the performance of AlScN HEMT structures grown by molecular beam epitaxy (MBE, blue symbols). [ 9,11,28,30 ] Lines of constant sheet resistance are indicated.…”

“…We showed that the barrier/channel interface can be improved to some extent by inserting a nominal AlN interlayer or reducing the growth temperature. [21] To date, there is no other report in the literature of MOCVD of AlScN reporting GRs higher than 0.006 nm s À1 . An enhancement in GR is necessary to reduce the degradation of the barrier/channel interface by diffusion during high-temperature MOCVD growth.…”

“…We showed that the barrier/channel interface can be improved to some extent by inserting a nominal AlN interlayer or reducing the growth temperature. [ 21 ]…”