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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 effects of growth parameters on deep levels in n-type 4H-SiC were investigated by deep level transient spectroscopy. It was seen that the formation of Z1/2 and EH6/7 centers were guided by the C/Si ratio and growth temperature rather than the growth rate.

β-Ga2O3 is gaining increasing attention from power device engineers owing to its wide bandgap and fabrication potential of low-cost, large-diameter substrates. Atomic-layer-deposited (ALD) Al2O3 has application potential for the gate insulation and surface passivation of β-Ga2O3 devices, which cannot incorporate a well-established SiO2/Si system. To improve the device performance and reliability, the effect of postdeposition annealing (PDA) on the gate insulation characteristics of Al/ALD-Al2O3/(001) β-Ga2O3 capacitors was comprehensively investigated. As in previous studies, PDA at 700 °C and higher sharply reduced the capacitor leakage current by three orders of magnitude. This threshold temperature was 100 °C lower than that for GaN devices. Space-charge-controlled field emission analysis revealed that the current reduction was achieved via conduction-band-offset enhancement from 1.45 to 2.2 eV. These changes were caused by Al2O3 crystallization, which started at 650 °C according to an x-ray diffraction analysis. Selective-area electron diffraction (SAED) patterns showed that the crystallized films comprised twinned γ-Al2O3, wherein the (111) planes are parallel to the sawtooth β-Ga2O3 (101) planes with epitaxial relations of γ-Al2O3 [ 0 1 ¯ 1 ] || β-Ga2O3 [010] and γ-Al2O3 [ 01 1 ¯ ] || β-Ga2O3 [010]. This epitaxy was realized by three-dimensional oxygen sublattice matching with relatively small misfits of less than 1%, 1%, and 8% along the γ-Al2O3 [ 2 1 ¯ 1 ¯ ] , [111], and [ 01 1 ¯ ] directions, respectively. Furthermore, the SAED patterns displayed diffraction spots specific to triaxially tripled γ-Al2O3. This is yet to be identified as δ-Al2O3. Contrary to expectations, PDA magnified the bias instability of β-Ga2O3 capacitors, supposedly owing to the Al2O3 and Ga2O3 solid-solution reaction, which contrasts with the previous significant improvement in GaN capacitors. However, PDA negligibly affected the β-Ga2O3 capacitor interface characteristics. This result also contrasts sharply with the previous results obtained for GaN capacitors that experienced a PDA-induced increase in both interface states and flat-band voltage. This apparent thermal stability of Al2O3/(001) β-Ga2O3 interface can be ascribed to the aforementioned small lattice misfit at the γ-Al2O3/(101) β-Ga2O3 interface, which contrasts with the 12% misfit at the γ-Al2O3/(0001) GaN interface. These findings form the foundation for developing technologies to enhance the performance and reliability of ALD-Al2O3/β-Ga2O3 devices. Specifically, based on them, a guideline for reducing the bias instability is proposed. [ABSTRACT FROM AUTHOR]

With a new structure of Ni/n-SiC/n+-SiC/Al, we have achieved a simultaneous observation of the dislocations in n-SiC epilayer and n+-SiC substrate by electron beam induced current (EBIC). The EBIC images were compared to the results of a depth-controlled wet etching in KOH+Na2O2. It has been found that each type of dislocations has its own signature in EBIC images in terms of the darkness, shape and orientation of the dark contrast. By changing the accelerating voltage of the electron beam, we can also observe the depth dependent presence of each type of dislocations and where and how the dislocation conversion happens. [ABSTRACT FROM AUTHOR]

The authors have investigated deep levels in as-grown and electron-irradiated p-type 4H-SiC epilayers by deep level transient spectroscopy. In as-grown epilayers, the D center and four deep levels are observed. In p-type 4H-SiC, reactive ion etching followed by thermal treatment (at 1150 °C) induces the HK0 (EV+0.79 eV) and HK2 (EV+0.84 eV) centers. By the electron irradiation, two deep levels at 0.98 eV (EP1) and 1.44 eV (EP2) are observed in all the samples irradiated at 116–400 keV, while two additional deep levels (EP3 and EP4) are observed only in the samples irradiated at 400 keV. After annealing at 950 °C, these centers are annealed out, and the HK4 (EV+1.44 eV) concentration is increased. By the electron irradiation at more than 160 keV followed by annealing at 950 °C, three deep levels are always observed at 0.30 eV (UK1), 0.58 eV (UK2), and 1.44 eV (HK4). These centers may be defect complexes including carbondisplacement-related defects. All the centers except for the D center are reduced to below the detection limit (1-3×1011 cm-3) by annealing at 1550 °C for 30 min. [ABSTRACT FROM AUTHOR]

Deep levels in n-type 4H-SiC epilayers have been investigated by deep level transient spectroscopy (DLTS). The Z1/2 and EH6/7 centers are dominant in as-grown samples. After electron irradiation at 116 keV, by which only carbon atoms may be displaced, the Z1/2 and EH6/7 concentrations are significantly increased. The Z1/2 and EH6/7 centers are stable up to 1500–1600 °C and their concentrations are decreased by annealing at 1600–1700 °C. In the irradiated samples, the trap concentrations of the Z1/2 and EH6/7 centers are increased with the 0.7 power of the electron fluence. The concentrations of the Z1/2 and EH6/7 centers are very close to each other in all kinds of samples, as-grown, as-irradiated, and annealed ones, even though the condition of growth, irradiation (energy and fluence), and annealing has been changed. This result suggests that both Z1/2 and EH6/7 centers microscopically contain the same defect such as a carbon vacancy. [ABSTRACT FROM AUTHOR]