Comparison of the physical, chemical and electrical properties of ALD Al₂O₃ on c‐ and m‐ plane GaN

Abstract

This study compares the physical, chemical and electrical properties of Al2O3 thin films deposited on gallium polar c‐ and nonpolar m ‐plane GaN substrates by atomic layer deposition (ALD). Correlations were sought between the film's structure, composition, and electrical properties. The thickness of the Al2O3 films was 19.2 nm as determined from a Si witness sample by spectroscopic ellipsometry. The gate dielectric was slightly aluminum‐rich (Al:O=1:1.3) as measured from X‐ray photoelectron spectroscopy (XPS) depth profile, and the oxide‐semiconductor interface carbon concentration was lower on c ‐plane GaN. The oxide's surface morphology was similar on both substrates, but was smoothest on c ‐plane GaN as determined by atomic force microscopy (AFM). Circular capacitors (50‐300 μm diameter) with Ni/Au (20/100 nm) metal contacts on top of the oxide were created by standard photolithography and e‐beam evaporation methods to form metal‐oxide‐semiconductor capacitors (MOSCAPs). The alumina deposited on c ‐plane GaN showed less hysteresis (0.15 V) than on m ‐plane GaN (0.24 V) in capacitance‐voltage (CV) characteristics, consistent with its better quality of this dielectric as evidenced by negligible carbon contamination and smooth oxide surface. These results demonstrate the promising potential of ALD Al2O3 on c ‐plane GaN, but further optimization of ALD is required to realize the best properties of Al2O3 on m ‐plane GaN. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A Comparison of N-Polar () GaN Surface Preparations for the Atomic Layer Deposition of Al2O3

“…12,13 Aluminum oxide (Al 2 O 3 ) is an excellent gate dielectric for IIInitride based devices due to its large bandgap (7∼9 eV), relatively high dielectric constant (∼9) and high thermal stability (up to 1000 • C). [14][15][16][17][18][19][20] Precise control of this dielectric's thickness is necessary to maintain the aspect ratio between the gate length and the oxide thickness for good high frequency performance. Atomic layer deposition (ALD) offers excellent thickness control for the deposition of such dielectrics, 21 but the initial condition of the substrate surface is crucial for the nucleation of the oxide layer and the subsequent surface morphology and interface electrical properties.…”

A Low‐Temperature Batch Process for the Deposition of High‐Quality Conformal Alumina Thin Films for Electronic Applications

“…The difference in flat band voltage between sweep directions, , can be used to estimate the total trapped charge in the films by multiplying by the oxide capacitance, as shown in previous reports. [ 35,36 ] Figure 6c shows the absolute trapped charge density as a function of deposition temperature. In addition to the general trend of reduced trapped charge with increasing temperature, for the films deposited in the range 60–150 °C, there is a reduction in trapped charge following voltage cycling between sweeps 1 and 3.…”

“…However, this difference in temperature dependence will be present in any system utilizing a carrier gas to introduce precursor to the chamber, indicating that a flow‐type system capable of producing high‐quality films in a higher temperature regime may have very different reaction kinetics when the temperature is reduced. [ 30,31,35,36 ] In summary, this simple model shows that pump‐type reactor designs have inherent advantages in terms of reaction kinetics at low deposition temperatures, which in turn influence deposition uniformity and conformality.…”

“…We found the following: at temperatures above 60 °C, the GPC (Figure 2a) increases until it reaches 120 °C, and RI (Figure 2a) also steadily increases until 150 °C. Films deposited at 35 °C display a high GPC, but they are not comparable in terms of stoichiometry and RI to those grown at higher temperatures. Their low refractive index (%1.56) and stoichiometry (see stoichiometry by XPS section) indicate that films grown at 35 °C have low densities and contain significant organic impurities which originate from unreacted TMA precursor (e.g., methyl groups).…”

Recent Developments and Prospects of Fully Recessed MIS Gate Structures for GaN on Si Power Transistors

“…For instance TMAH etches any plane of GaN, except for the (0001) c-plane, while it etches m-plane at a considerably lower rate than other semi-polar planes allowing, for instance, it to achieve rough a-plane oriented sidewall (composed of microscopic m-faces) and smooth m-plane oriented ones [78,79]. In the few studies carried out on different non-polar planes, it is clear that GaN crystallographic orientation impacts the effect of surface treatments on electrical characteristics [79,112,[129][130][131] or that sidewall formation has a significant impact on device performance (in comparison with a planar etched structure) [127]. As a consequence, is it crucial to improve the understanding of how the GaN crystal orientation and 3D gate cavity with sidewalls formation impacts recessed gate devices' performance.…”