Query: 4H-SiC

title: Characterization of SiO2/4H SiC Interfaces in 4H SiC MOSFETs: A Review
abstract: This paper gives an overview on some state of the art characterization methods of SiO2/4H SiC interfaces in metal oxide semiconductor field effect transistors (MOSFETs) In particular, the work compares the benefits and drawbacks of different techniques to assess the physical parameters describing the electronic properties and the current transport at the SiO2/SiC interfaces (interface states, channel mobility, trapping phenomena, etc. First, the most common electrical characterization techniques of SiO2/SiC interfaces are presented (e.g. capacitance and current voltage techniques, transient capacitance, and current measurements) Then, examples of electrical characterizations at the nanoscale (by scanning probe microscopy techniques) are given, to get insights on the homogeneity of the SiO2/SiC interface and the local interfacial doping effects occurring upon annealing. The trapping effects occurring in SiO2/4H SiC MOS systems are elucidated using advanced capacitance and current measurements as a function of time. In particular, these measurements give information on the density ~1011 cm 2) of near interface oxide traps (NIOTs) present inside the SiO2 layer and their position with respect to the interface with SiC (at about 1 2 nm) Finally, it will be shown that a comparison of the electrical data with advanced structural and chemical characterization methods makes it possible to ascribe the NIOTs to the presence of a sub stoichiometric SiOx layer at the interface.

title: Influence of annealing temperature on structure and photoelectrical performance of b Ga2O3/4H SiC heterojunction photodetectors
abstract: In this manuscript, an ultralow dark current solar blind photodetector based on b Ga2O3/4H SiC heterojunction is generated by depositing b Ga2O3 thin film on n type 4H SiC substrates using Pulse Laser Deposition method. It is found that the excellent performances of our device with ultralow dark current (0.167 nA) as well as high Iphoto/Idark ration (384.3) are obtained with thermal annealing at optimized temperature, which is due to the improvement of interface defects in the b Ga2O3/4H SiC heterojunction through high temperature annealing. Moreover, the detectivity and linear dynamic range of the device are high as 8.23 x 1011 Jones and 51.70 dB, respectively, along with faster response speed (a rise time of 0.18 s and a decay time of 0.31s) which are attributed to the co effect of reducing in defects at the interface of heterojunction and the existence of appropriate amount of mixed crystal orientation in b Ga2O3 films with the optimizing the annealing temperature. The electronic transport mechanism in the b Ga2O3/4H SiC heterojunction photodetector is proposed in details with the energy band diagram.

title: Effects of Ti, Si, Mg and Cu additions on interfacial properties and electronic structure of Al(111)/4H SiC(0001) interface: A first principles study
abstract: In this study, the structural stability and electronic properties of Al(111)/4H SiC(0001) interface, as well as the effects of Ti, Si, Mg and Cu additions on the interfacial adhesive strength are investigated via the first principles method. Surface energy calculations show that 4H SiC(0001) with C termination is more active than Si termination. Moreover, polar covalent bonds are formed across Al/4H SiC interface. The results of separation energies suggest that the introduction of Ti and Si can improve the adhesive strength of C terminated Al(111)/4H SiC(0001) interface, whereas Mg and Cu have the opposite effect. According to the analysis of interfacial electronic structure, the covalent bonds across Al/4H SiC interface are further enhanced with the addition of Ti and Si atoms, contributing to the improved adhesive strength in this case. However, the interactions between interfacial atoms are weakened with Mg and Cu doped in C terminated interface, which results in the decrease of interfacial adhesion strength. Our calculations provide a guide to experiments on the design of 4H SiC reinforced Al matrix composites with tailored properties.

title: Highly sensitive 4H SiC pressure sensor at cryogenic and elevated temperatures
abstract: The slow etching rate of conventional micro machining processes is hindering the use of bulk silicon carbide materials in pressure sensing. This paper presents a 4H SiC piezoresistive pressure sensor utilising a laser scribing approach for fast prototyping a bulk SiC pressure sensor. The sensor is able to operate at a temperature range from cryogenic to elevated temperatures with an excellent linearity and repeatability with a pressure of up to 270 kPa. The good optical transparency of SiC material allows the direct alignment between the pre fabricated piezoresistors and the scribing process to form a diaphragm from the back side. The sensitivities of the sensor were obtained as 10.83 mV/V/bar at 198 K and 6.72 mV/V/bar at 473 K, which are at least a two fold increment in comparison with other SiC pressure sensors. The high sensitivity and good reliability at either cryogenic and elevated temperatures are attributed to the profound piezoresistive effect in p type 4H SiC and the robust p n junction which prevents the current from leaking to the substrate. This indicates the potential of utilising the laser scribing approach to fabricate highly sensitive bulk SiC pressure sensors for harsh environment applications.

title: Interface carbon defects at 4H SiC(0001)/SiO2 interfaces studied by electron spin resonance spectroscopy
abstract: We study an electron spin resonance (ESR) signal of carbon dangling bond defects at 4H SiC(0001)/SiO2 interfaces, which we call an "interface carbon defect." The ESR signal is close to a c axial type of the PbC centers (interfacial carbon dangling bonds) that have originally been found in porous SiC/SiO2 interfaces. The interface carbon defects were always formed with an areal density of 3 4 x 1012 cm 2 after the standard dry oxidation of 4H SiC(0001) surfaces. They act as electron traps and decrease the amount of free electrons in the channel region, consequently reducing the field effect mobility of Si face 4H SiC MOSFETs. They were eliminated by optimum post oxidation anneals (POAs) in either NO or POCl3 environment. Furthermore, POCl3 POAs at 1000 degC introduced a high density (1.7 x 1012 cm 2) of phosphorus donors into the channel region, increasing the free carrier density as compared with the case of NO POAs.

title: Isotropic piezoresistance of p type 4H SiC in (0001) plane
abstract: In this work, the isotropic piezoresistance in the (0001) plane of p type 4H SiC was discovered by means of the hole energy shift calculation and the coordinate transformation. These results were also confirmed by the measurement of the piezoresistance using a bending beam method. The fundamental longitudinal and transverse piezoresistive coefficients p11 and p12 were found to be 6.43 x 10 11 Pa 1 and 5.12 x 10 11 Pa 1, respectively. The isotropy of the piezoresistance in the basal plane of p type 4H SiC is attributed to the isotropic hole energy shift under uniaxial strain. This interesting phenomenon in p type 4H SiC is promising for the design and fabrication of mechanical sensors and strain engineered electronics since high sensitivity and consistent performance can be achieved regardless of the crystallographic orientation.

title: High temperature tolerance of the piezoresistive effect in p 4H SiC for harsh environment sensing
abstract: 4H silicon carbide based sensors are promising candidates for replacing prevalent silicon based counterparts in harsh environments owing to their superior chemical inertness, high stability and reliability. However, the wafer cost and the difficulty in obtaining an ohmic contact in the metallization process hinders the use of this SiC polytype for practical sensing applications. This article presents the high temperature tolerance of a p type 4H SiC piezoresistor at elevated temperatures up to 600 degC. A good ohmic contact was formed by the metallisation process using titanium and aluminium annealed at 1000 degC. The leakage current at high temperatures was measured to be negligible thanks to a robust p n junction. Owing to the superior physical properties of the bulk 4H SiC material, a high gauge factor of 23 was obtained at 600 degC. The piezoresistive effect also exhibits good linearity and high stability at high temperatures. The results demonstrate the capability of p type 4H SiC for the development of highly sensitive sensors for hostile environments.

title: Demonstration of 4H SiC Digital Integrated Circuits Above 800 degC
abstract: Short term demonstrations of packaged 4H SiC junction field effect transistor (JFET) logic integrated circuits (ICs) at temperatures exceeding 800 degC in air are reported, including a 26 transistor 11 stage ring oscillator that functioned at 961 degC ambient temperature believed unprecedented for electrical operation of a semiconductor IC. The expanded temperature range should assist temperature acceleration testing/qualification of such ICs intended for long term use in applications near 500 degC ambient, and perhaps spawn new applications. Ceramic package assembly leakage currents inhibited the determination of some intrinsic SiC device/circuit performance properties at these extreme temperatures, so it is conceivable that even higher operating temperatures might be obtained from SiC JFET ICs by employing packaging and circuit design intended/optimized for T <inline formula> <tex math notation="LaTeX"\ge800$ /tex math>/inline formula> degC.

title: Optical charge state control of spin defects in 4H SiC
abstract: Defects in silicon carbide (SiC) have emerged as a favorable platform for optically active spin based quantum technologies. Spin qubits exist in specific charge states of these defects, where the ability to control these states can provide enhanced spin dependent readout and long term charge stability. We investigate this charge state control for two major spin qubits in 4H SiC, the divacancy and silicon vacancy, obtaining bidirectional optical charge conversion between the bright and dark states of these defects. We measure increased photoluminescence from divacancy ensembles by up to three orders of magnitude using near ultraviolet excitation, depending on the substrate, and without degrading the electron spin coherence time. This charge conversion remains stable for hours at cryogenic temperatures, allowing spatial and persistent patterning of the charge state populations. We develop a comprehensive model of the defects and optical processes involved, offering a strong basis to improve material design and to develop quantum applications in SiC.Defects in silicon carbide represent a viable candidate for realization of spin qubits. Here, the authors show stable bidirectional charge state conversion for the silicon vacancy and divacancy, improving the photoluminescence intensity by up to three orders of magnitude with no effect on spin coherence.

title: Electronic structures and magnetic properties of (Ni,Al) co doped 4H SiC: A first principles study
abstract: Based on density functional theory (DFT) first principles method, we have investigated the electronic structures and magnetic properties of (Ni,Al) co doped 4H SiC system. Various configurations of Ni sites have been considered to confirm the most stable geometric construction. Comparing with pure 4H SiC, the magnetic moment of Ni doped 4H SiC is increased, which is attributed to the hybridization of Ni:4s and C:2p orbitals. Moreover, we found that it is the 3d orbital of Ni that induces the spin polarized state in Ni doped 4H SiC. In addition, the origin of ferromagnetic coupling between Ni doped 4H SiC has been predicted to be the ferromagnetic orders activated by the Ni0:3d C:2p Ni2:3d coupling chains. For (Ni,Al) co doped system, we found that ferromagnetic stability is reduced significantly. For (2Ni, V Si co doped 4H SiC system, the antiferromagnetic state is more stable than ferromagnetic state with E FM of 97.2 meV, and the system changes from ferromagnetism to anti ferromagnetism. These results provide a new route for the potential applications of dilute magnetic semiconductors in spintronic devices by employing doped 4H SiC.