Abstract A normally-off hybrid-gate p-GaN high-electron-mobility transistor (HEMT) is presented in this paper. The gate region is designed as a parallel connection between the Schottky-gate and the metal–insulator–semiconductor gate by inserting a dielectric layer under part of the gate metal. Compared to the conventional Schottky-gate p-GaN HEMT, the fabricated hybrid-gate p-GaN HEMT showed a higher threshold voltage of 3.2 V (increases by 167%), and the maximum transconductance is only a slight decrease (reduces by 23%). At the same time, the forward gate leakage current of the hybrid-gate structure is smaller. Furthermore, through simulation, we revealed that the increase in the threshold voltage originated from the delayed full opening of the two-dimensional electron gas. And we also find that the parameters of the gate dielectric layer have a great influence on the performance of the device. The results show that the hybrid-gate structure is a more promising device structure.
BiOCl nanosheets nucleated and grew on cottage cheese-like SiC substrate via hydrothermal procedure, through which a tight heterojunction was formed. SiC/BiOCl composites with varied morphologies were acquired that the formation of BiOCl was involved with different form of carbon existed on surface of SiC. The photocatalytic mechanism analysis revealed that the combination of SiC and BOC significantly enhanced photocatalytic activities owing to the improved visible light utilization, efficient separation of photo-generated carriers, and promoted reactive area. The main active species during the photocatalytic reaction was determined as ·O2− radical by additionally adding trapping agent into the reactant. The SiC-BOC composites showed much higher photoactivities in photocurrent responses and photocatalytic degradation of TC-HCl, which mainly attributed to the well-built heterointerface promoted by Bi-C bonds and the interlaced structure obtained by increasing exposure of (010) facets in BiOCl. The nucleation, growth and combination architecture of BiOCl was all influenced by the involvement of SiC.
Abstract As the representative of substrate material, gallium nitride (GaN) has excellent mechanical properties and high thermal stability. Achieving high surface flatness is critical for subsequent epitaxial growth and device fabrication processes. Chemical mechanical polishing (CMP) technique of GaN is commonly one of the most effective ways to achieve atomically smooth surfaces. However, the current process is difficult to meet the needs of industrial development due to the characteristics of low material removal rate. Assisted enhanced CMP technique is deemed to possess significant potential due to its improved processing efficiency and surface topography quality. Herein, a variety of auxiliary enhanced CMP systems are designed and studied. In this review, recent advances both in conventional and assisted enhanced CMP of GaN are comprehensive presented, with a focus on their potential applications in various fields. The mechanism and design strategy of the process are discussed and summarized. The key issues in machining atomically flattened surface are outlined, and future strategies for sustainable development are also proposed. This review provides a novel perspective on GaN processing and offers more inspiration for future research to realize its development and commercial application.
We have developed MOCVD-grown, C-doped, abrupt heterojunction InP-GaAsSb-InP DHBTs which feature a very small V/sub CE/ offset voltage <0.1 V and a low turn-on voltage (J/sub c/=1 A/cm/sup 2/) at V/sub BE/=0.3 V, by taking advantage of the staggered band line-up at InP-GaAsSb interfaces: the GaAsSb conduction band sits above the InP conduction band, eliminating any possibility of current blocking at the B-C junction; instead, the GaAsSb base injects electrons ballistically (with ΔE/sub C/=0.1-0.3 eV) into the widegap InP collector when they travel with a high saturated drift velocity and low rates of impact ionization. One of the fundamental advantages of InP-GaAsSb-InP DHBTs is that they can be implemented without compositional grading and with nominally abrupt interfaces: the turn-on and offset voltages are therefore determined by the band line-ups, doping, and junction areas. They are not altered by the effectiveness of compositional grading or pulse doping schemes that are intended to eliminate conduction-band spikes and barriers. Other important advantages of MOCVD-grown GaAsSb bases are that they can be C-doped to 10/sup 20/ cm/sup -3/ without H-passivation effects, and that the low p-type Schottky barrier heights on antimonide compounds lead to low resistance base ohmic contacts, with measured base contact resistances lower than 10/sup -7/ Ωcm/sup -2/. Our DHBT prototypes display a base current ideality factor of n/sub B/=1.1 and a current gain of 15. The fabrication of InP-GaAsSb-InP DHBTs is presented, with particular attention to the growth details and their impact on device performance.
We have measured the slit width dependence of the linewidth of the first-order Raman lines in 4H-SiC at room temperature. The Raman spectra were fitted into Voigt profile. The Raman linewidth monotonously increased with the slit width, which indicated that the obtained linewidth contained the contribution of instrumental bandpass. To exclude the contribution of instrumental bandpass and get the accurate data for linewidth, a mathematical method was used to eliminate the instrumental bandpass due to the finite slit width. Then the Raman linewidth at zero-slit width was employed to calculate the phonon lifetime by energy-time uncertainty relation. Results showed that for undoped 4H-SiC, the phonon lifetime was in the sequence of E 2 (TA) > E 2 (TO) > A 1 (LO). In addition, the impurity content effect on phonon lifetime was discussed. Results showed that phonon lifetime was shortened with increasing impurity content. However, it was found that the phonon lifetime of E2(TA) mode was more sensitive to impurity content than that of E2(TO) mode.
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