Structure of Ultrathin Native Oxides on III–Nitride Surfaces

Abstract

When pristine material surfaces are exposed to air, highly reactive broken bonds can promote the formation of surface oxides with structures and properties differing greatly from bulk. Determination of the oxide structure is often elusive through the use of indirect diffraction methods or techniques that probe only the outermost layer. As a result, surface oxides forming on widely used materials, such as group III-nitrides, have not been unambiguously resolved, even though critical properties can depend sensitively on their presence. In this study, aberration corrected scanning transmission electron microscopy reveals directly, and with depth dependence, the structure of ultrathin native oxides that form on AlN and GaN surfaces. Through atomic resolution imaging and spectroscopy, we show that the oxide layers are comprised of tetrahedra-octahedra cation-oxygen units, in an arrangement similar to bulk θ-AlO and β-GaO. By applying density functional theory, we show that the observed structures are more stable than previously proposed surface oxide models. We place the impact of these observations in the context of key III-nitride growth, device issues, and the recent discovery of two-dimensional nitrides.

Wurtzite AlN(0001) Surface Oxidation: Hints from Ab Initio Calculations

“…Recently, Dycus et al have revealed the structure of ultrathin oxides that form on AlN surfaces by experiment . There are some similarities between our simulated structures and the experimental results, as shown in Figure S3.…”

“…However, there are many metastables, the so-called "transition alumina" structures exiting, one of which is cubic γ-Al 2 O 3 . 33 In this study, γ- 6 There are some similarities between our simulated structures and the experimental results, as shown in Figure S3. In…”

“…Among the III–V groups of nitrides, aluminum nitride (AlN) has attracted a great attention owing to its excellent physical properties, such as high electrical resistivity (>4 × 10 8 Ω cm), high thermal conductivity (3.2 W cm –1 K –1 ), and low coefficient of thermal expansion (4.03–6.0 × 10 –6 K –1 ). , Therefore, it is widely applied as high-temperature ceramics and refractories, − for instance, as the belly of the blast furnace. However, AlN is sensitive to oxygen and tends to be oxidized or corroded under high temperature, which seriously restricts its applications.…”

Effects of surface treatment on Fermi level pinning at metal/GaN interfaces formed on homoepitaxial GaN layers

“…Although several reports on surface treatment have been published, it is difficult to remove this oxide layer completely using ordinary solutions [22][23][24][25][26][27] . Recently, it has been reported that the surface oxide layer formed by long-term air exposure after specific chemical treatments has a crystalline nature [28][29][30] .…”

Observation of polarity-switchable photoconductivity in III-nitride/MoSx core-shell nanowires

“…For instance, on one hand, such vertical and high-aspect-ratio geometry (1) enables core-shell device architecture in the radial direction which facilitates efficient light absorption and photo-generated charge-carrier extraction for high-efficient photovoltaic or photodetection applications 17,18 , and (2) provides high density of surface sites for artificial photosynthesis or photoelectrochemical photodetection [19][20][21][22] . On the other hand, ultrahigh surface areas naturally induce a high density of surface states 23,24 , which could act as charge trapping centers and harmful to the performance of nanoscale devices. Thus, effective surface passivation approaches are then required to remove or suppress such surface states to boost nanowire device performance 25 .…”