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This study investigated the impact of the post-deposition annealing (PDA) process on the material and electrical properties of copper oxide (Cu2O) and nickel oxide (NiO) thin films deposited on a silicon carbide (SiC) substrate. Through radiofrequency (RF) sputtering, these films were subjected to PDA in a nitrogen (N2) and oxygen (O2) gas environment. Remarkably, the Cu2O films resisted phase transition following the N2 PDA process but exhibited a transition to cupric oxide (CuO) after undergoing the O2 PDA process. The symmetry of Cu 2p in the as-deposited Cu2O film was excellent; however, the phase-transformed CuO films exhibited an increase in binding energy and the emergence of satellite peaks. The Ni 2p exhibited various defects, such as nickel vacancies (VNi) and interstitial oxygen (Oi), in response to the different PDA atmospheres. The rectification ratios of the N2-annealed Cu2O and NiO devices were determined as 1.50 × 107 and 4.01 × 106, respectively, signifying a substantial enhancement by a factor of approximately 789 for the Cu2O/SiC device and 124 for the NiO/SiC device relative to their non-annealed counterparts. The findings of this study indicate that meticulous control of deposition for potential p-type materials such as Cu2O and NiO can significantly improve the performance in applications involving high-throughput and low-cost electronics. [ABSTRACT FROM AUTHOR]

Aiming at the issues of low efficiency, high cost, and environmental pollution associated with silicon carbide (SiC) substrates in the polishing process, a method of tribochemical mechanical polishing of SiC substrates in the dry state (Dry Tribochemical Mechanical Polishing, DTCMP) is proposed. The effect of different process parameters (abrasive type, abrasive size, abrasive content, polishing plate speed, polishing load, solid phase oxidant content) on the polishing efficiency and surface quality of single-crystal silicon carbide substrates was investigated. The results show that diamond abrasive is more suitable for the tribochemical mechanical polishing of silicon carbide. Optimal test parameters are achieved when the abrasive size is W1, the abrasive content is 4 g, the polishing plate speed is 70 r/min, the polishing load is 20.685 kPa, and the solid phase oxidant sodium percarbonate is added at 10 g. Single-crystal 6H-SiC substrates with a surface roughness of approximately 20 nm were polished using the optimal process parameters, finanlly resulting in a surface roughness of Ra of 3.214 nm. The DTCMP method for polishing SiC substrate has less heat loss than water-based polishing method, enabling higher interface temperature and lower activation energy required for reactions. This method can realize green, efficient and high-quality polishing of SiC substrates.

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A systematic study of epi-AlGaN/GaN on a SiC substrate was conducted through a comprehensive analysis of material properties and device performance. In this novel epitaxial design, an AlGaN/GaN channel layer was grown directly on the AlN nucleation layer, without the conventional doped thick buffer layer. Compared to the conventional epi-structures on the SiC and Si substrates, the non-buffer epi-AlGaN/GaN structure had a better crystalline quality and surface morphology, with reliable control of growth stress. Hall measurements showed that the novel structure exhibited comparable transport properties to the conventional epi-structure on the SiC substrate, regardless of the buffer layer. Furthermore, almost unchanged carrier distribution from room temperature to 150 °C indicated excellent two-dimensional electron gas (2DEG) confinement due to the pulling effect of the conduction band from the nucleation layer as a back-barrier. High-performance depletion-mode MIS-HEMTs were demonstrated with on-resistance of 5.84 Ω·mm and an output current of 1002 mA/mm. The dynamic characteristics showed a much smaller decrease in the saturation current (only ~7%), with a quiescent drain bias of 40 V, which was strong evidence of less electron trapping owing to the high-quality non-buffer AlGaN/GaN epitaxial growth. [ABSTRACT FROM AUTHOR]

In this paper, AlGaN/GaN high electron mobility transistors (HEMTs) with etched-fin gate structures fabricated to improve device linearity for Ka-band application are reported. Within the proposed study of planar, one-etched-fin, four-etched-fin, and nine-etched-fin devices, which have 50-μm, 25-μm, 10-μm, and 5-μm partial gate widths, respectively, the four-etched-fin gate AlGaN/GaN HEMT devices have demonstrated optimized device linearity with respect to the extrinsic transconductance ( G m ) value, the output third order intercept point (OIP3), and the third-order intermodulation output power (IMD3) level. The IMD3 is improved by 7 dB at 30 GHz for the 4 × 50 μm HEMT device. The OIP3 is found to reach a maximum value of 36.43 dBm with the four-etched-fin device, which exhibits high potential for the advancement of wireless power amplifier components for Ka band applications. [ABSTRACT FROM AUTHOR]

A study of 1.7 kV normally-off p-GaN gate high-electron-mobility transistors (HEMTs) on SiC substrates is presented. The fabricated p-GaN HEMT with a gate-drain spacing LGD = 5 µm exhibited a threshold voltage of 1.10 V, a maximum drain current of 235 mA/mm, an ON/OFF ratio of 108, and a breakdown voltage of 440 V. Benefiting from the semi-insulating and high-critical-electric-field substrate, the p-GaN HEMT with LGD = 23 µm achieved the remarkably high breakdown voltage of 1740 V with substrate grounded. This breakdown voltage is very high compared with the reported values for p-GaN HEMTs on silicon substrates with substrate grounded. The vertical breakdown voltage for the p-GaN-on-SiC material exceeded 3 kV with substrate grounded. In addition, the maximum drain current at 500 K was 48% of that at 300 K with a negligible threshold voltage shift. These results indicate the substantial potential of p-GaN gate HEMTs on SiC substrates for high-voltage power applications. [ABSTRACT FROM AUTHOR]

The intrinsic n-type of epitaxial graphene on SiC substrate limits its applications in microelectronic devices, and it is thus vital to modulate and achieve p-type and charge-neutral graphene. The main groups of metal intercalations, such as Ge and Sn, are found to be excellent candidates to achieve this goal based on the first-principle calculation results. They can modulate the conduction type of graphene via intercalation coverages and bring out interesting magnetic properties to the entire intercalation structures without inducing magnetism to graphene, which is superior to the transition metal intercalations, such as Fe and Mn. It is found that the Ge intercalation leads to ambipolar doping of graphene, and the p-type graphene can only be obtained when forming the Ge adatom between Ge layer and graphene. Charge-neutral graphene can be achieved under high Sn intercalation coverage (7/8 bilayer) owing to the significantly increased distance between graphene and deformed Sn intercalation. These findings would open up an avenue for developing novel graphene-based spintronic and electric devices on SiC substrate. [ABSTRACT FROM AUTHOR]

A systematic study of epi-AlGaN/GaN on a SiC substrate was conducted through a comprehensive analysis of material properties and device performance. In this novel epitaxial design, an AlGaN/GaN channel layer was grown directly on the AlN nucleation layer, without the conventional doped thick buffer layer. Compared to the conventional epi-structures on the SiC and Si substrates, the non-buffer epi-AlGaN/GaN structure had a better crystalline quality and surface morphology, with reliable control of growth stress. Hall measurements showed that the novel structure exhibited comparable transport properties to the conventional epi-structure on the SiC substrate, regardless of the buffer layer. Furthermore, almost unchanged carrier distribution from room temperature to 150 °C indicated excellent two-dimensional electron gas (2DEG) confinement due to the pulling effect of the conduction band from the nucleation layer as a back-barrier. High-performance depletion-mode MIS-HEMTs were demonstrated with on-resistance of 5.84 Ω·mm and an output current of 1002 mA/mm. The dynamic characteristics showed a much smaller decrease in the saturation current (only ~7%), with a quiescent drain bias of 40 V, which was strong evidence of less electron trapping owing to the high-quality non-buffer AlGaN/GaN epitaxial growth.

In this paper, AlGaN/GaN high electron mobility transistors (HEMTs) with etched-fin gate structures fabricated to improve device linearity for Ka-band application are reported. Within the proposed study of planar, one-etched-fin, four-etched-fin, and nine-etched-fin devices, which have 50-μm, 25-μm, 10-μm, and 5-μm partial gate widths, respectively, the four-etched-fin gate AlGaN/GaN HEMT devices have demonstrated optimized device linearity with respect to the extrinsic transconductance (Gm) value, the output third order intercept point (OIP3), and the third-order intermodulation output power (IMD3) level. The IMD3 is improved by 7 dB at 30 GHz for the 4 × 50 μm HEMT device. The OIP3 is found to reach a maximum value of 36.43 dBm with the four-etched-fin device, which exhibits high potential for the advancement of wireless power amplifier components for Ka band applications.

The intrinsic n-type of epitaxial graphene on SiC substrate limits its applications in microelectronic devices, and it is thus vital to modulate and achieve p-type and charge-neutral graphene. The main groups of metal intercalations, such as Ge and Sn, are found to be excellent candidates to achieve this goal based on the first-principle calculation results. They can modulate the conduction type of graphene via intercalation coverages and bring out interesting magnetic properties to the entire intercalation structures without inducing magnetism to graphene, which is superior to the transition metal intercalations, such as Fe and Mn. It is found that the Ge intercalation leads to ambipolar doping of graphene, and the p-type graphene can only be obtained when forming the Ge adatom between Ge layer and graphene. Charge-neutral graphene can be achieved under high Sn intercalation coverage (7/8 bilayer) owing to the significantly increased distance between graphene and deformed Sn intercalation. These findings would open up an avenue for developing novel graphene-based spintronic and electric devices on SiC substrate.

Wide bandgap semiconductors are ideal materials for the application of high power density, high frequency and low- loss power electronic devices, owning to the advantages of wide bandgap, high electron saturation velocity, and high breakdown field. Attributed to the high thermal conductivity, high chemical stability and high heat resistance of silicon carbide (SiC), epitaxy of wide bandgap semiconductors on SiC is promising to exploit the advantages of wide bandgap semiconductors and improve the performance of wide bandgap semiconductor devices. Benefiting from the continuous quality-improvement and cost-reduction of SiC substrates, wide bandgap semiconductors grown on SiC substrates are ushering in an explosive growth. Epitaxy of high quality wide bandgap semiconductors on SiC substrates is critical to the performance and reliability of wide bandgap semiconductor devices. This paper summarizes the recent progress obtained on epitaxial growth of SiC, gallium nitride (GaN) and gallium oxide (Ga2O3) on SiC substrates. In addition, the prospective of wide bandgap semiconductors grown on SiC substrates for high-performance electronics are prospected. [ABSTRACT FROM AUTHOR]

Currently, the GaN-on-silicon high electron mobility transistor (HEMT) is a promising candidate to replace the Si Metal Oxide Semiconductor Field Effect Transistor (MOSFET) for high power electronics circuits. However, self-heating is still a challenging issue to be addressed, especially for high-current applications. In this paper, a GaN-on-Si HEMT with a diamond (Dia) heat spreader is proposed to suppress the self-heating effect. The performance of the proposed device is analyzed and compared with conventional GaN-on-Si and also GaN-on-SiC devices. The analysis was carried-out using technology computer aided design. The GaN-on-Si with diamond heat spreader suppresses the self-heating in the device and achieves higher saturation drain current than conventional GaN-on-Si. In addition, GaN-on-Si with Diamond heat spreader yields a higher transconductance and cut-off frequency than GaN-on-Si. This improved structure will provide a low cost device with enhanced thermal characteristics for higher power applications. [ABSTRACT FROM AUTHOR]

For cutting a SiC substrate coated with a metal film stably, a novel ductile-mode dicing process was developed using a blade made of a single body of poly-crystalline diamond (PCD) with only 50 μm in thickness. It is difficult for a conventional diamond blade with metal binder to cut the SiC substrate in a straight line accurately due to insufficient buckling strength. In addition, self-sharpening effect of the cutting edge is suppressed by adhesion of metal film to blade surface. In this study, a rake face and a flank face of the cutting edge were formed by irradiating pulsed laser light tangentially to the cutting edge. Under the high speed rotation condition of 30,000 rpm (500 s-1), the developed PCD blade acts on the workpiece with the continuous cutting edge in a stable posture due to the inertial force of the rotation, and the depth of cut per a cutting edge is about 5 nm. Under these conditions, the ultrafine cutting tip of the metal film also becomes on the order of nanometers. 4H-SiC substrate 350 μm in thickness with Au / Ni / Ti film was cut using the developed PCD blade. Under the half cut condition, there was no chipping or crack on the surface, and the bottom of the groove was finished in a mirror state. Under the full cut condition with a width of 50 μm, the SiC substrate and the metal film were cut at once, and any crack did not occur at the interface between SiC and the metal film. As the result, it was demonstrated that ductile mode machining was realized and the metal film did not adhere to the cutting edge.

Abstract AlGaN/GaN heterostructures were grown on "on-axis" and 2° off (0001) 4H-SiC substrates by metalorganic vapor phase epitaxy (MOVPE). Structural characterization was performed by transmission electron microscopy. The dislocation density, being greater in the on-axis case, is gradually reduced in the GaN layer and is forming dislocation loops in the lower region. Steps aligned along [ 1 1 ̅ 00 ] in the off-axis case give rise to simultaneous defect formation. In the on-axis case, an almost zero density of steps is observed, with the main origin of defects probably being the orientation mismatch at the grain boundaries between the small not fully coalesced AlN grains. V-shaped formations are observed in the AlN nucleation layer, but are more frequent in the off-axis case, probably enhanced by the presence of steps. These V-shaped formations are completely overgrown by the GaN layer, during the subsequent deposition, presenting AlGaN areas in the walls of the defect, indicating an inter-diffusion between the layers. Finally, at the AlGaN/GaN heterostructure surface in the on-axis case, V-shapes are observed, with the AlN spacer and AlGaN (21% Al) thickness on relaxed GaN exceeding the critical thickness for relaxation. On the other hand, no relaxation in the form of V-shape creation is observed in the off-axis case, probably due to the smaller AlGaN thickness (less than 21% Al). The AlN spacer layer, grown in between the heterostructure, presents a uniform thickness and clear interfaces. [ABSTRACT FROM AUTHOR]

Graphene directly grown on an 4H-SiC (0 0 0 1) substrate by chemical vapor deposition was studied: it was shown that Si evaporation process is not completely halted during graphene growth when T G  ≥ 1400 °C, the SiC substrate decomposes at the position of graphene coverage. AFM and Raman spectrum results reveal that carbon concentration significantly influences graphene growth rate and morphology/structure. It is found that the quality of graphene film depends on the growth temperature and the flow of carbon source. We develop a new gradient growth method to produce a feasible graphene material for electronic devices. Graphene grown by this method has a flat-morphology structure, low wrinkle density, high crystal quality, good uniformity, and outstanding electrical transport properties. Nitrogen doping has an n-type doping effect on graphene carrier concentration. The main component of nitrogen-bond type is the graphitic configuration. The graphene material with nitrogen doping reaches a record mobility of 9010 cm 2 /V·s by room temperature Hall effect measurement, indicating graphene grown by gradient method with suitable nitrogen doping could yield a high quality film comparable to that by traditional method. [ABSTRACT FROM AUTHOR]

InP/InGaAsSb double heterojunction bipolar transistors (DHBTs) with an Au subcollector were fabricated on a SiC substrate by using a wafer bonding technique. The thermal resistance ( R\textsf {th} ) of a fabricated DHBT with a \textsf 0.35 \times \textsf 8.0\,\,\mu \textm emitter is 62% lower than that of a DHBT with the same epitaxial layer structure on an InP substrate. Thanks to the lower R\textsf {th} , the DHBT operates at a collector current density ( JC ) of over 25 mA/ \mu \textm^\textsf 2 without any lowering of current gain. The DHBT exhibits a record ft of 695 GHz at JC of 21 mA/ \mu \textm^\textsf 2 owing to the reduced emitter charging time by suppressing the Kirk effect. [ABSTRACT FROM PUBLISHER]

In this paper the recent use AlGaN/GaN high electron mobility transistors (HEMTs) and integrated circuits on both semi‐insulating silicon carbide (SiC) and silicon substrates for radio communication in the microwave and mm‐wave frequency range is described. AlGaN/GaN monolithically microwave integrated circuits (MMICs) are extremely useful for point‐to‐point (P2P)‐links in the backbones of the 4th and upcoming 5th generation of mobile communication networks as power amplifiers, as they provide a great amount of linear power. At the same time GaN‐based power conversion electronics has driven the advancement of the growth of AlGaN/GaN heterostructures on conductive silicon (111) substrates. This again has indirectly led to advancements in the growth capabilities of AlGaN/GaN heterostructures on highly‐resistive (HR) silicon substrates. The paper gives examples of transistors and microstrip transmission‐line‐based MMICs realized in a direct comparison of GaN on s.i. SiC and GaN on HR‐silicon. Constraints and performances for highly‐efficient MMICs are discussed up to mm‐wave frequencies beyond 100 GHz. [ABSTRACT FROM AUTHOR]

Monocrystalline SiC has long been recognised as an ideal third-generation semiconductor material for application in situations where there is high frequency, high power and high voltage. Because of the hardness, stiffness and strength of monocrystalline SiC, these materials are extremely difficult to machine in order to produce the extremely flat, smooth and damage-free surfaces required in many industrial applications. This paper presents the results of plane grinding experiments which were carried out using a metal-bonded diamond wheel. The process parameters of these have demonstrated a significant influence on surface roughness. Surface quality improved and roughness decreased as the wheel feed rate decreased. On the substrate surfaces, the particle trajectory density increased closer to the centre, producing better surface quality. At large feed rates, the material removed is mainly brittle fracture, and the plough scratch widths and gully depths on the ground surface are greater. At small feed rates, plastic removal predominates, becoming more significant closer to the centre and giving a smoother surface. Median and transverse cracks occur in the subsurface damaged layer, and the crack depths are consistent with the surface roughness Rz and gully morphology. Then, the critical grit depth of cut and the maximum undeformed substrate thickness values under different grinding conditions were calculated in order to analyse the characteristics of the subsurface damage and the material removal mechanism. Finally, an optimised process was achieved using orthogonal experiments, with processing parameters for rough, half-fine and fine grinding. This process gives flat substrates with surface roughness Ra 0.012 μm, SSD < 4 μm and TTV < 3 μm, which achieves the same level of precision as lapping. [ABSTRACT FROM AUTHOR]