Aluminum Oxide at the Monolayer Limit via Oxidant‐Free Plasma‐Assisted Atomic Layer Deposition on GaN

Abstract

Atomic layer deposition (ALD) is an essential tool in semiconductor device fabrication that allows the growth of ultrathin and conformal films to precisely form heterostructures and tune interface properties. The self‐limiting nature of the chemical reactions during ALD provides excellent control over the layer thickness. However, in contrast to idealized growth models, it is challenging to create continuous monolayers by ALD because surface inhomogeneities and precursor steric interactions result in island growth. Thus, the ability to create closed monolayers by ALD would offer new opportunities for controlling interfacial charge and mass transport in semiconductor devices, as well as for tailoring surface chemistry. Here, encapsulation of c‐plane gallium nitride (GaN) with ultimately thin (≈3 Å) aluminum oxide (AlOx) is reported, which is enabled by the partial conversion of the GaN surface oxide into AlOx using sequential exposure to trimethylaluminum (TMA) and hydrogen plasma. Introduction of monolayer AlOx decreases the work function and enhances reactivity with phosphonic acids under standard conditions, which results in self‐assembled monolayers with densities approaching the theoretical limit. Given the high reactivity of TMA with surface oxides, the presented approach likely can be extended to other dielectrics and III–V‐based semiconductors, with relevance for applications in optoelectronics, chemical sensing, and (photo)electrocatalysis.

Modular Assembly of Vibrationally and Electronically Coupled Rhenium Bipyridine Carbonyl Complexes on Silicon

“…Despite a theoretical spin−orbit splitting of 0.86 ± 0.05 eV, 48,49 the P 2p peaks are broad (fwhm: ∼2.09 and 1.98 eV for PA−C 6 and PA−C 11 ) and nearly symmetric [for PA−C 6 slightly asymmetrical to lower binding energy (BE)], which is indicative of a mixed binding motif (inset in Figure 3b). 50,47 Interestingly, the best P 2p fit of PA−C 6 (Figure 3a) suggests a mixed binding configuration, of which the monodentate mode is slightly dominant (54.2%), whereas for the PA−C 11 (Figure 3b), a predominantly monodentate (71.0%) binding motif can be observed. We note that this distribution of binding modes was found on all measured samples (three in total for each PA type used).…”

“…Due to the steric hindrance of trimethylaluminum (TMA), 46 the formation of a closed AlO x surface layer is not possible for a three-cycle growth, which is reflected by the significantly lower PA coverage on a 0.25 nm AlO x coating. Recently, 47 we demonstrated PA−C 11 surface functionalization of a continuous ∼0.3 nm thick monolayer AlO x grown on gallium nitride with a PA coverage of 4.5 ± 0.3 nm −2 , suggesting that the 0.45 nm AlO x on Si is, indeed, continuous and that the PA coverage depends on the availability of AlO x surface binding sites until a coverage of ∼6.09 ± 0.57 nm −2 is reached. We note that the underlying silicon substrate is entirely inaccessible by phosphonate chemistry under the applied reaction conditions (SI Figure 13a).…”

“…SAMPs of 6-hydroxyhexylphosphonic acid (≥98% (GC); referred to as PA–C 6 ) and 11-hydroxyundecylphosphonic acid (≥99% (GC); referred to as PA–C 11 ) (SiKÉMIA, Montpellier, France) were prepared via an immersion technique recently reported in detail for monolayer AlO x grown on c -plane, Ga-polar GaN substrates …”

“…The binding energy of the hemispherical analyzer was calibrated with in situ sputter-cleaned silver (Ag 3d, 1118.51 eV), gold (Au 4f, 1402.73 eV), and copper (Cu 2p, 554.07 eV) standards (given in kinetic energy) with an accuracy of 0.025 eV. An instrumental broadening of 0.30 eV was determined by fitting the measured Ag 3d core level spectrum of an Ag calibration sample with a Voigt function . No charge neutralization was performed, as no measurable binding energy shifts were observed for nonfunctionalized substrates).…”

Electronically Tunable Transparent Conductive Thin Films for Scalable Integration of 2D Materials with Passive 2D–3D Interfaces

“…We show that nc-C substrates can be produced on a large scale with tunable sheet carrier concentrations. Using atomic layer deposition (ALD), we conformally coat the nc-C layer with an amorphous aluminum oxide (AlO x ) layer, having a controlled thickness (down to 1 nm and even below [23,24] ). While the conductive (ρ < 0.01 Ω cm) and ultrasmooth (rms roughness ≈0.2 nm) carbon coating serves as the transparent electrode, the conformal alumina layer acts as a high-k dielectric (k ≈7 [25] ) spacer with tunable impedance.…”