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As diamond possesses only deep dopants, certain conventional physics and characterization methods are not applicable to diamond devices, owing to the explicit or implicit assumption of shallow dopants. To resolve this limitation, the capacitance–voltage (C–V) characteristics of metal–insulator–semiconductor (MIS) capacitors formed on a semiconductor substrate with deep and compensating dopants were successfully formulated. Based on these equations, methods for accurately estimating the MIS capacitor properties were developed and validated through their application in the analysis of an actual MIS capacitor formed on a boron-doped hydrogen-terminated diamond substrate. The high-frequency C–V characteristic of the capacitor exhibited a prominent dip specific to deep dopants. However, the dip depth was considerably shallower than theoretically expected. This C–V characteristic was accurately reproduced theoretically, assuming the presence of a surficial diamond layer that contains acceptors with an activation energy of 0.23 eV, which is less than the value 0.37 eV for boron, and has a thickness of the extrinsic Debye length (40 nm in this study) or larger. The insulator charge of the MIS capacitor was estimated as −4.6 × 1012 cm−2 in units of electronic charge, which is sufficiently large to induce two-dimensional hole gas. The interface-state density was 1.4 × 1012 cm−2 eV−1 for interface-state energies of 0.3–0.5 eV above the valence band maximum. Hence, the proposed methodology and the possible presence of the reduced activation energy layer will guide the development of diamond-based devices. [ABSTRACT FROM AUTHOR]

In recent years, Gallium Nitride (GaN)-based metal-insulator-semiconductor high-electron-mobility transistors (MISHEMTs) have attracted interest in high-power and high-frequency applications. The breakdown mechanism in E-mode GaN MISHEMTs with carbon doping in the GaN buffer grown on a Silicon (Si) substrate (Sub) was investigated using technology computer-aided design simulations. Results showed that GaN MISHEMTs without Si Sub had a breakdown voltage (BV) of 600 V. However, after adding Si Sub to the GaN buffer layer, the electric field (EF) increased, creating a vertical breakdown through the total buffer thickness, therefore, BV was reduced to around 240 V. On the other hand, BV is increased to approximately >1100 V, and the Electric field is reduced after employing a carbon deep acceptor with the proper doping concentration in this device. The GaN MISHEMTs with Si Sub is presented as threshold voltage +1.5 V with transconductance of 700 mS/mm, which is an excellent result compared to GaN MISHEMTs without Si Sub. Eventually, the study device depicted higher BV performance compared to other C-doped GaN HEMT devices. This suggests that the designed GaN MISHEMTs device could effectively be used in power semiconductor devices with optimum performance. [ABSTRACT FROM AUTHOR]

The influence of Al2O3 atomic-layer deposition (ALD) temperature on the electric characteristics of Al / A l 2 O 3 / ( 2 ¯ 01) β-Ga2O3 capacitors was investigated focusing on the positive-bias instability (PBI) of the capacitors. The current in the capacitors increased with ALD temperature, mostly because of the reduced energy barrier height for the electron field emission from the substrate and less negative Al2O3 charge, as revealed by the analysis conducted assuming a space-charge-controlled field emission process. The PBI tests were conducted for cumulative voltage stressing times vastly ranging from 3 × 10−6 to 4 × 105 s. The capacitance–voltage (C–V) characteristics of the capacitors for an ALD temperature of 100 °C displayed negative shifts in the middle of voltage stressing, unlike those for the other ALD temperatures. The bias stability of the capacitors was found to be considerably improved by high-temperature (450 °C) ALD. Additionally, the C–V characteristic shifts caused by the voltage stressing were theoretically reproduced quite accurately, assuming a model proposed in this study. In the simulations, the trap distributions in the Al2O3 films were assumed to be uniform both spatially and energetically. Importantly, the experimental results for various stressing voltages were excellently fitted by the simulations that assumed the same trap distribution. The trap densities in the Al2O3 films thus estimated reduced from 1.2 × 1020 to 2.2 × 1019 cm−3 eV−1 for ALD temperatures of 100–450 °C. This reduction in the trap densities was a major cause of the bias stability enhancement for high-temperature ALD. Moreover, the trap density as a function of ALD temperature qualitatively agreed with the aforementioned Al2O3 charge generated by the current measurements. This agreement provides a strong basis for the validity of the PBI model proposed in this study. [ABSTRACT FROM AUTHOR]

The current conduction in negatively biased metal/Al2O3/diamond capacitors with various gate materials and diamond surface terminations was comprehensively characterized by assuming a space-charge-controlled field emission (SCC-FE) process, yielding the following results. The current-feeding carriers were field-emitted from the electrode that had a barrier height lower than that of the opposing electrode. Specifically, in an Au-gate oxygen-terminated diamond capacitor, holes were likely to be emitted from the Al2O3/diamond interface states, whereas, in Al-gate oxygen-terminated, Au-gate hydrogen-terminated, and Al-gate hydrogen-terminated diamond capacitors, electrons were emitted from the gate. The barrier heights at the Al/Al2O3 and Au/Al2O3 interfaces were estimated as 1.6–1.7 and 2.8 eV, respectively. However, the analysis of the hole emission from the interface states is left for future studies. Although the substrate of the oxygen-terminated diamond capacitor remained weakly depleted even for highly negative gate voltages, the conduction current was observed as mentioned earlier. To analyze the mechanism for this conduction, the diffusion and drift currents in the depleted substrate were quantitatively estimated, ascribing the current conduction to the diffusion current. As these results could not be obtained by using the conventional graphical methods based on model-specific plots, such as the Fowler–Nordheim and Poole–Frenkel plots, the SCC-FE analysis proved to be a powerful tool for investigating the current conduction in metal-insulator-semiconductor capacitors. [ABSTRACT FROM AUTHOR]

As previously reported, postdeposition annealing at 800 °C and higher simultaneously crystallizes atomic-layer-deposited (ALD) Al2O3 films and reduces the current in Al/ALD-Al2O3/(0001) GaN capacitors by two orders of magnitude. This current reduction is caused by the enhancement of conduction band offset from 1.4 to 1.8 eV, as revealed by the space-charge-controlled field emission analysis. Selected area electron diffraction (SAED) patterns demonstrate that the crystallized films consist of twinned (111)-oriented cubic γ-Al2O3 with an epitaxial relation of Al2O3 ⟨ 0 1 ¯ 1 ⟩ ∥ GaN ⟨ 2 1 ¯ 1 ¯ 0 ⟩. The SAED patterns additionally include spots that are specific to triaxially tripled γ-Al2O3. The aforementioned epitaxy is due to the similarity of hexagonal close-packed sublattices between oxygen on a (111) γ-Al2O3 plane and nitrogen on a (0001) GaN plane. However, the hexagonal close-packed lattice constant of γ-Al2O3 is 12% smaller than that of GaN, necessitating domain matching epitaxy. The thickness of the interfacial transition layer caused by the large misfit is estimated to be thinner than four monolayers of oxygen sublattice, by using the methodology developed here. Based on these results, the effect of Al2O3 crystallinity on the characteristics of Al2O3/GaN capacitors, such as conduction current, dielectric breakdown, interface states, and bias instability, was comprehensively captured. According to x-ray diffraction analyses, Al2O3 films crystallize at 700 °C, which is ∼100 °C lower than the threshold temperature estimated by transmission electron microscope observations. This difference was possibly caused by locally crystallized Al2O3 films, as confirmed by the slightly reduced current. These findings form a basis for improving ALD-Al2O3 films as gate insulator. [ABSTRACT FROM AUTHOR]