GaN-based high-electron-mobility transistor structures with homogeneous lattice-matched InAlN barriers grown by plasma-assisted molecular beam epitaxy

Abstract

Metal-polar In 0.17 Al 0.83 N barriers, lattice-matched to GaN, were grown under N-rich conditions by plasma-assisted molecular beam epitaxy. The compositional homogeneity of these barriers was confirmed by plan-view high-angle annular dark-field scanning transmission electron microscopy and atom probe tomography. Metal-polar In 0.17 Al 0.83 N/(GaN)/(AlN)/GaN structures were grown with a range of AlN and GaN interlayer (IL) thicknesses to determine the optimal structure for achieving a low two-dimensional electron gas (2DEG) sheet resistance. It was determined that the presence of a GaN IL was necessary to yield a 2DEG sheet density above 2 × 10 13 cm −2 . By including AlN and GaN ILs with thicknesses of 3 nm and 2 nm, respectively, a metal-polar In 0.17 Al 0.83 N/GaN/AlN/GaN structure regrown on a GaN-on-sapphire template yielded a room temperature (RT) 2DEG sheet resistance of 163 / . This structure had a threading dislocation density (TDD) of ∼5 × 10 8 cm −2 . Through regrowth on a free-standing GaN template with low TDD (∼5 × 10 7 cm −2 ), an optimized metal-polar In 0.17 Al 0.83 N/GaN/AlN/GaN structure achieved a RT 2DEG sheet resistance of 145 / and mobility of 1822 cm 2 V −1 s −1 . High-electron-mobility transistors with output current densities above 1 A mm −1 were also demonstrated on the low-TDD structure.

Room temperature photoluminescence from InxAl(1−x)N films deposited by plasma-assisted molecular beam epitaxy

“…16,17 This microstructure is common to InAlN films synthesized by MBE, with the exception of a recent report on compositionally uniform InAlN grown by MBE under N-rich conditions (III/V ratio ¼ 0.3) at a very slow growth rate ($1 nm/min). 19 These conditions are far from those used in this study and electron microscopy confirms that our films possess this microstructure.…”

Conduction band fluctuation scattering due to alloy clustering in barrier layers in InAlN/GaN heterostructures

“…In contrast, moderate correlation lengths indicate severe compositional inhomogeneity, and thus lead to minimal mobilities. In real heterostructures, correlation lengths approximately equal to cluster widths of around 10 nm, 5,8 which are always larger than the values minimizing the mobility. In the Λ range that can readily be reached, the mobility is slightly dependent on N s , but increases rapidly with increasing correlation length.…”

“…Due to large differences in binding energies between Al-N (2.88 eV) and In-N (1.98 eV) bonds, InAlN/GaN heterostructures, especially those grown by molecular beam epitaxy, generally exhibit severe lateral compositional inhomogeneity. [5][6][7] In compositionally inhomogeneous InAlN layers, alternate AlN-rich and InNrich regions form columnar clusters with widths about 10 nm. 5,8 Alloy clustering causes 2DEG subband energy fluctuations and InAlN conduction band fluctuations (see Figure 1), both affects the electron transport properties of InAlN/GaN heterostructures.…”

“…[5][6][7] In compositionally inhomogeneous InAlN layers, alternate AlN-rich and InNrich regions form columnar clusters with widths about 10 nm. 5,8 Alloy clustering causes 2DEG subband energy fluctuations and InAlN conduction band fluctuations (see Figure 1), both affects the electron transport properties of InAlN/GaN heterostructures. Ahmadi et al 9 and Liu et al 10 studied the subband energy fluctuation scattering (SEFS) and suggested that the SEFS played an important role in the electron transport, especially for lower 2DEG sheet densities.…”

Indium incorporation dynamics in N-polar InAlN thin films grown by plasma-assisted molecular beam epitaxy on freestanding GaN substrates

“…Growth temperatures are generally chosen to be low enough to avoid thermal decomposition of InN: around 500 1C for metal-polar InAlN and 550 1C for Npolar InAlN [4,12,23]. Recently, InAlN layers grown in the N-rich regime at somewhat higher temperatures have been demonstrated with improved compositional homogeneity [26,27].…”