[en] Buffer related electron trapping and hot electron injection are responsible for R _on degradation in devices, but the effects of substrate termination are still uncertain. In this work, both positive and negative substrate bias are applied to investigate the different vertical trapping mechanisms in 650 V gallium nitride (GaN) power devices. R _on shows an instant and significant increase under vertical bias stress, and the magnitude of downward buffer electron trapping induced R _on increase is relatively larger than that induced by upward trapping. Additionally, the substrate floated and grounded GaN devices are also submitted to both off-state and semi-on-state stresses to investigate the effects of substrate termination on hot electron injection induced R _on increase. The intensity of the upward electron trapping increases faster with temperature resulting in a higher R _on increase than the downward situation. The hot electron effect is only obvious when the substrate is grounded, suggesting that the main injection destination is not in the buffer. The substrate floated device exhibits a lower R _on increase after both off-state and semi-on-state stresses at elevated temperatures. Substrate floated packages are suggested to ensure reliable dynamic performance of device, especially for high voltage application design. (paper)

[en] A high laser-induced damage threshold (LIDT) TiO₂/SiO₂ high reflector (HR) at 1064 nm is deposited by e-beam evaporation. The HR is characterized by optical properties, surface, and cross section structure. LIDT is tested at 1064 nm with a 12 ns laser pulse in the one-on-one mode. Raman technique and scanning electron Microscope are used to analyze the laser-induced modification of HR. The possible damage mechanism is discussed. It is found that the LIDT of HR is influenced by the nanometer precursor in the surface, the intrinsic absorption of film material, the compactness of the cross section and surface structure, and the homogeneity of TiO₂ layer. Three typical damage morphologies such as flat-bottom pit, delamination, and plasma scald determine well the nanometer defect initiation mechanism. The laser-induced crystallization consists well with the thermal damage nature of HR

[en] Three-dimensional (3D) high-temperature Hall sensors are strongly required in various applications such as in the automotive and aircraft engines and in the diagnostic system of the thermonuclear reactors. In this paper, we propose a novel Hall sensor based on the wide-bandgap GaN-based materials on a single chip with greatly reduced area which can simultaneously detect 3D magnetic fields at high temperature up to 650 K. The device is analysed and demonstrated by performing the technology computer-aided design simulations, and significantly improved performances are achieved by employing space isolation and passivation scheme to effectively reduce the carrier interference from each dimension. Finally, high current-related magnetic sensitivities are found and the typical values are 128.6, 88.1, and 49.9 V A⁻¹ T⁻¹ on x, y and z axes, respectively, at room temperature. And the temperature coefficients are as low as −286.4, −366.8, and −202.9 ppm K⁻¹, respectively. Moreover, dramatically improved cross-sensitivities are revealed and the maximum value is less than 1.0% at B ≤ 1.0 T which is much lower compared with other currently reported data. The work provides a new technical approach to realize a single-chip 3D magnetic sensor which is promising especially for high-temperature applications. (paper)

[en] Transparent conductive Al-doped zinc oxide (AZO) films with highly (0 0 2)-preferred orientation were deposited on quartz substrates at room temperature by RF magnetron sputtering. Optimization of deposition parameters was based on RF power, Ar pressure in the vacuum chamber, and distance between the target and substrate. The structural, electrical, and optical properties of the AZO thin films were investigated by X-ray diffraction, Hall measurement, and optical transmission spectroscopy. The 250 nm thickness AZO films with an electrical resistivity as low as 4.62 x 10^-4 Ω cm and an average optical transmission of 93.7% in the visible range were obtained at RF power of 300 W, Ar flow rate of 30 sccm, and target distance of 7 cm. The optical bandgap depends on the deposition condition, and was in the range of 3.75-3.86 eV. These results make the possibility for light emitting diodes (LEDs) and solar cells with AZO films as transparent electrodes, especially using lift-off process to achieve the transparent electrode pattern transfer

[en] In this work, we performed an investigation on the electrical characteristics of the interfaces of SiON/AlGaN and SiON/GaN by fabricating a partially gate-recessed metal-insulator-semiconductor high electron mobility transistor (MIS-HEMT) and a fully gate-recessed metal-insulator-semiconductor field-effect transistor (MIS-FET). The fabricated MIS-HEMT exhibits a smaller static on-resistance (R _on) of 12.7 Ω · mm, while the MIS-FET achieves the normally-off operation. As a result of over-etching in the gate trench, a higher trap state density of 2 × 10¹³ cm⁻²eV⁻¹ at the SiON/GaN interface in comparison to SiON/AlGaN interface (8 × 10¹² cm⁻²eV⁻¹), leading to a more obvious degradation of subthreshold swing, was extracted after performing the high temperature I _DS−V _GS tests. In addition, compared with the MIS-FET, the traps distributed at the SiON/AlGaN interface are found to be located at a deeper energy level, which make the device more stress sensitive and can cause a greater threshold voltage (V _th) shift in the drain-bias stress measurement. The drain-bias stress at off-state increases the ionized trap density and makes the ionized traps unrecoverable within 1000 s in the MIS-HEMT. This work reveals the different properties of traps states at the SiON/AlGaN and SiON/GaN interfaces, and their effects on the device reliability. (paper)

[en] This paper reports on the studies of current collapse phenomenon induced by surface trapped charges during gate pulse switching in AlGaN/GaN heterostructure high-electron-mobility transistors. A physical-based model, taking into account the distribution features of the applied electric field along the surface of the device barrier layer near the drain-side gate corner, is proposed to analyse the electron trapping and de-trapping processes at the ionized donor-like traps during the device off-state or on-state process. Then the model is analysed and verified by TCAD simulation and laboratory measurement data. The morphology of the current collapse related AlGaN surface is investigated by SEM and AFM characterizations. The dynamic process and quantitative relationship between the electric field and trapped electron density are determined and analysed in detail. The spatial distributions of the trapped electrons and excess free electrons along AlGaN barrier surface are achieved by using the proposed physical model. The work provides a distinct perspective to understand and quantify the current collapse mechanism in AlGaN/GaN power devices, and it can also assist engineers for a better device design. (paper)

[en] Two tungsten/tungsten oxide/Indium–Tin Oxide (W/WO_3-x/ITO) memristors were fabricated for studying comparatively the effects of W/WO_3-x junction on their synaptic performances, in which one is ohmic (Ohm-type device) and the other is rectified (Rec-type device). The characterization results show that Ohm-type device exhibits rich synaptic properties, including the controllable synapse weight update by adjusting the input pulse amplitude, interval, and number, as well as the transformation from the paired-pulse facilitation (PPF) to the paired-pulse depression (PPD) by only changing the pulse width. However, the Rec-type device manifests the nonconventional synaptic behavior and the bowknot-shaped I–V curves. The fitting of I–V curves by the various carrier transport modes demonstrates the bulk mechanism for the Ohm-type device and Schottky mechanism for the Rec-type device. Therefore, we suggest that oxygen vacancy injection and migration in WO_3-x layer lead to the presence of synaptic properties in the Ohm-type device, while the rectified W/WO_3-x junction and the variable conductance of WO_3-x layer lead to the nonconventional synaptic properties and bowknot-shaped I–V curves. This report revealed the complexity of memristors, and emphasizing the necessity to carefully select the material combination and design the device structures for realizing the synaptic properties.

[en] In this paper, an electrode-pair model is proposed and demonstrated for the first time to accurately extract the electrical resistance parameters of the planar metal-semiconductor ohmic contacts. Different from the conventional transmission line model, the proposed model layout features a series of separated electrode pairs with the same electrode distance but various widths. Meanwhile, an equivalent circuit for contact resistance composition is set up to clearly specify the contribution of each resistance component to the overall contact performance. The semiconductor sheet resistances underneath the contact and outside the contact area are treated as completely independent variables. The proposed scheme is modeled theoretically and analyzed by the TCAD simulations, and the validity of the model is verified by the experimental data. Finally, the variance of the sheet resistance underneath the contact after annealing treatment can be distinguished by the model and hence more actual and precise specific contact resistance is achieved. This work provides a distinct perspective to understand and quantify the electrical characteristics of the semiconductor ohmic contacts, and it can also assist engineers for a better electrode layout design.