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We demonstrate an Nb 2 O 5 / β - Ga 2 O 3 metal–insulator–semiconductor (MIS) hetero-junction diode with Nb 2 O 5 as the high-k dielectric insulator for more efficient electric field management resulting in enhanced breakdown characteristics compared to a β - Ga 2 O 3 Schottky barrier diode. Nb 2 O 5 dielectric films were grown using atomic layer deposition and exhibited a high dielectric constant of 50. The high dielectric constant resulted in a 5 × lower electric field at the metal/dielectric interface in the MIS diode compared to the metal/ β - Ga 2 O 3 interface in the Schottky barrier diode. With good electron conduction in forward bias enabled by the negative conduction band offset of Nb 2 O 5 with respect to β - Ga 2 O 3 , the MIS design led to a 3 × improvement in the reverse blocking voltage with a slight trade-off in the specific on-resistance. Overall, a 3.3 × increase in the power figure of merit was observed (3.25 MW / cm 2 for the Schottky diode and 10.8 MW / cm 2 for the MIS diode). A detailed analysis of the energy band line-up and the forward and reverse current transport mechanisms are also presented using analytical modeling and 2D technology computer-aided design simulations. [ABSTRACT FROM AUTHOR]

Ternary dielectrics with varying composition formed by alloying two binary oxides can enable tunable optical and electrical properties for advanced technological applications. Atomic layer deposition (ALD) gives precise control over ternary dielectric composition through the ability to finely tune the precursor pulsing ratio. This work presents ALD development of Si-rich SixTi1−xO2 dielectrics with varying composition (x), along with spectroscopic and electrical characterization of their properties. Stoichiometry of the SixTi1−xO2 films was determined using X-ray photoelectron spectroscopy. Their composition-dependent refractive index, energy bandgap, and reflectance show promise for diverse optical applications ranging from anti-reflective coatings in photovoltaics to optical waveguides. This work also reports a first comparative study of SixTi1−xO2 films prepared by thermal (T-) and plasma-enhanced (PE-) ALD with varying Si composition and deposition temperatures. Deposition rates of 0.67–0.92 Å/cycle were obtained for SixTi1−xO2 films with x = 0.5–0.91 deposited using PE-ALD at 250 °C, which were higher than that of T-ALD at 200 °C (0.42–0.05 Å/cycle). PE-ALD also exhibited a high deposition rate of 0.81 Å/cycle for SixTi1−xO2 film with x = 0.91 at a low growth temperature of 150 °C. The PE-ALD Si-rich silica–titania films show substantially lower (100×) leakage current densities than the thermally deposited films, along with higher breakdown fields for decreasing deposition temperature. A dielectric constant as low as ∼5 was achieved for PE-ALD SixTi1−xO2 films with high Si (x = 0.91) content. [ABSTRACT FROM AUTHOR]

β-Ga2O3 based enhancement mode transistor designs are critical for the realization of low loss, high efficiency next generation power devices with rudimentary driving circuits. A large positive flatband voltage (Vfb) of 10.6 V in β-Ga2O3 metal-oxide-semiconductor capacitors, with the ability to fine-tune it between 3.5 V and 10.6 V, using a polycrystalline AlN charge trap layer has been demonstrated. This can enable enhancement mode operation over a wide doping range. An excellent Vfb retention of ∼ 97% for 104 s at 55 °C was exhibited by the gate stacks after charge trapping, hence reducing the requirement of frequent charge injection cycles. In addition, low gate leakage current density (Jg) for high negative gate voltages (Vg ∼ −60 V) indicates the potential of this gate stack to enable superior breakdown characteristics in enhancement mode transistors. [ABSTRACT FROM AUTHOR]

High performance gate stacks are critically needed for the development of β-Ga2O3 power transistors. Significant improvement in the performance of β-Ga2O3 gate stacks is demonstrated in this work by using SiO2 as an interlayer dielectric between Al2O3 and β-Ga2O3. The presence of SiO2 results in an 800× reduction in gate leakage current along with a 1.7× increase in the electric breakdown field. Additionally, the capacitance-voltage characteristics show an increase in flat band voltage (from 0.74 V to 3.25 V) that can enable normally off power transistors. The lowest interface trap density (Dit) of 5.1 × 1010 cm−2 eV−1 for the SiO2/β-Ga2O3 interface has been demonstrated through the use of a piranha clean before SiO2 deposition on β-Ga2O3 for the first time. Reduction (8×) in Dit, hysteresis (from 0.17 V to 0.05 V), and border trap density indicate substantial improvement in the quality of the β-Ga2O3/gate dielectric interface for the Al2O3/SiO2 bilayer stack as compared to only Al2O3. [ABSTRACT FROM AUTHOR]

This work demonstrates a solution to the problem of increase in Schottky barrier height (#8709;B) with thermal annealing (thermal instability) in unpinned (low #8709;B) Ti/TiO2/n-Ge metal-interfacial layer (IL)-semiconductor (MIS) contacts through plasma nitridation of the TiO2 layer. Unlike TiO2, unpinned (#8709;B =0.09 eV) TiOxNy contacts are thermally stable for anneals up to 30 min at 400°C. The thermal stability improves with increasing nitrogen concentration ([N], 2.5-9.5%) and is independent of thickness (2-5 nm) for [N]=9.5%. Additionally, the plasma nitridation process is shown to increase the oxygen vacancy concentration (n-type doping) and reduce the #8709;B dependence on TiOxNy thickness in unannealed TiOxNy contacts. Enhanced thermal stability is attributed to the incorporated nitrogen acting as a diffusion barrier that prevents contact pinning through reduction of the TiO2 layer by contact metal during the anneal, as well as preserves the amorphous nature of the IL along with its fixed charge and interfacial dipoles that contribute to #8709;B reduction. [ABSTRACT FROM AUTHOR]