n-SiC Substrates Research Articles

193 nm immersion photodetector with an ultra-high EQE of 83.7%

With the development of chip to high-density integration, the requirement of lithography precision is higher and higher. In this process, controlling the power of the lithography exposure light source is very important to improve the quality of the chip. However, most detectors are unable to conduct light detection in liquid environments, especially in the aspects of real-time detection and calibration of light power in immersion deep ultraviolet lithography. In this paper, the AlN film epitaxial on n-SiC substrate by MOCVD is used as the photoelectrode, based on which an immersion detector with a quick response to 193 nm vacuum ultraviolet (VUV) light is fabricated. Impressively, under 0 V bias, the detector achieves a high responsiveness (130 mA/W) and an EQE up to 83.7% under an excitation with lower light power (45 nW), illustrating its ability to perform highly efficient detection of light signals and underwater imaging in weak-light environment. In addition, the detector also has the shortest detection wavelength when compared with the immersion photodetectors reported so far. At the same time, the simulated immersion lithography monitoring experiment shows that the detector has good real-time monitoring ability. In a word, this work provides a novel method for detecting underwater light power and can work as reference for realizing the real-time monitoring of immersive lithography light sources in future applications.

Адсорбция атомов Ga и Cl и молекулы GaCl на карбиде кремния: модельный подход

Within the scope of the Haldane – Anderson model metallic and ionic contri-butions to the adsorption energy are calculated for the Ga and Cl atoms ad-sorbed on the C- and Si-faces of p- and n-SiC substrates. It is shown firstly that for all considered cases we obtain that ionic contribution is greater than metallic contribution. Secondly, in the case of adsorption on the p-SiC sub-strate value of the model of adsorption energy for Ga is greater than for Cl while in the case of adsorption on the n-SiC opposite inequality is realized. For the description of the GaCl adsorption on SiC substrate simple ionic model is put forward. Comparison with the results of other authors demonstrates valid-ity of the proposed models.

ZnMgO-nanorod-based Schottky Light-emitting Diode Fabricated on n-SiC Substrate Using Low-temperature Method

We fabricated a ZnMgOnanorodbased Schottky lightemitting diode (LED) on an n-SiC substrate using a lowtemperature growth method. Study about structural properties of ZnMgO nanorods was carried out by field emission scanning electron microscopy (FE-SEM) and fourier-transforms infrared spectroscopy (FTIR). The electrooptical properties of the ZnMgO nanorods were investigated using photoluminescence (PL), electroluminescence (EL) and current–voltage measurements. The values of ideality factor, barrier height and series resistance were calculated 3.22 1.1eV and 187Ω, respectively. The understanding of the optical properties and luminescence performance of the ZnMgO-nanorod based Schottky LED is important for applications in optical nanodevices. The PL measurements of the ZnMgO nanorods revealed a blueshift of the ultraviolet (UV) emission peak, which suggests their potentials for the development of tunable optical nanodevices. The blueshift of the UV emission was attributed to the diffusion of Mg and formation of the ternary ZnMgO alloy. The EL spectra exhibited an emission band covering the visible range from 40 nm to 700 nm. Gaussian functions were employed to simulate the experimental data, which revealed that the emission band can be regarded as a superposition of violet, blue, green and yellow emissions.

Fabrication of vertically conducting near ultraviolet LEDs on SiC substrates

In this work, GaN-based vertically conducting near ultraviolet light-emitting diodes (LEDs) were grown on n-SiC substrates by metal-organic chemical vapor deposition. 10 pairs or 20 pairs of Si-doped n-Al0.2Ga0.8N/n-GaN distributed Bragg reflectors (DBRs) were used to improve the performance of the LEDs. The central reflected wavelength of the DBRs structures agreed well with the emission wavelength of the LEDs. A 389 nm near ultraviolet electroluminescence (EL) emission peak could be clearly observed in all the LED samples in our study. The EL intensity of LEDs was obviously enhanced because of the application of DBRs. Angle-dependent EL spectra were measured as well. For all the measurement angle region, the near ultraviolet EL emission intensity of the LEDs with DBRs were higher than that of the LED without DBRs.

Simulation and fabrication of N-polar GaN-based blue-green light-emitting diodes with p-type AlGaN electron blocking layer

N-polar GaN-based blue-green light-emitting diodes (LEDs) with p-AlGaN electron blocking layer (EBL) were numerically investigated by simulation and experimentally grown on vicinal C-face SiC substrates by metal–organic chemical vapor deposition. By numerical simulation, we can find that p-AlGaN EBL in N-polar LEDs is able to play a more important role in blocking electron overflow than that in Ga-polar LEDs due to the reversed polarization, which leads to a high output power and internal quantum efficiency. Besides, the holes injection efficiency is enhanced in N-polar LED, resulting in a lower turn-on voltage. In experimental studies, N-polar LEDs based on different numbers of quantum wells were grown on vicinal C-face n-SiC substrates. When a forward bias is applied to the epitaxial N-polar LED with two quantum wells, a strong blue-green emission located at 480 nm can be observed. This work indicates that N-polar group-III nitrides have great potential in the application of optoelectronic devices.

Electrical characterization of 4H-SiC metal–oxide–semiconductor structure with Al2O3 stacking layers as dielectric

Interface defects and oxide bulk traps conventionally play important roles in the electrical performance of SiC MOS device. Introducing the Al2O3 stack grown by repeated anodization of Al films can notably lower the leakage current in comparison to the SiO2 structure, and enhance the minority carrier response at low frequency when the number of Al2O3 layers increase. In addition, the interface quality is not deteriorated by the stacking of Al2O3 layers because the stacked Al2O3 structure grown by anodization possesses good uniformity. In this work, the capacitance equivalent thickness (CET) of stacking Al2O3 will be up to 19.5 nm and the oxidation process can be carried out at room temperature. For the Al2O3 gate stack with CET 19.5 nm on n-SiC substrate, the leakage current at 2 V is 2.76 × 10−10 A/cm2, the interface trap density at the flatband voltage is 3.01 × 1011 eV−1 cm−2, and the effective breakdown field is 11.8 MV/cm. Frequency dispersion and breakdown characteristics may thus be improved as a result of the reduction in trap density. The Al2O3 stacking layers are capable of maintaining the leakage current as low as possible even after constant voltage stress test, which will further ameliorate reliability characteristics.

The property optimization of n-GaN films grown on n-SiC substrates by incorporating a SiNx interlayer

We presented the epitaxial growth of n-GaN films on n-SiC substrates with n-Al0.3Ga0.7N buffer and SiNx interlayer by metal organic vapor phase epitaxy. In order to optimize the properties of n-GaN films, a comparative investigation was performed by modifying SiNx deposition time and its insert location. Under the optimal growth parameters of SiNx, the full width at half maximum values of GaN $$(0002)$$ and $$(10\bar{1}2)$$ diffraction peaks effectively reduced to 208 and 226 arcsec, respectively. Simultaneously, molten NaOH based wet etchings were used to verify the reduction of the dislocation densities in GaN films. Good vertical conducting characteristics in n-GaN/n-SiC homo-type heterojunction were achieved by inserting SiNx into n-GaN film. Additionally, Raman and low-temperature photoluminescence measurements were employed to determine the stress state in GaN film.

Determination of Band Structure at GaAs/4H-SiC Heterojunctions

Introduction: Heterojunctions are widely used for fabricating high performance electrical and optical devices. The heterojunction fabricated by conventional epitaxial growth generally introduces a large number of crystalline defect densities at the interface due to the large differences in crystal lattice and thermal expansion coefficient. To solve these difficulties a variety of wafer bonding methods have been employed to fabricate semiconductor hetero-structure. Among them the most effective candidate is surface activated bonding (SAB) [1, 2]. In this method, surfaces of substrates are activated by the irradiation of Ar fast atom beams prior to bonding and consequently bring into contact in a vacuum condition. It enables us to fabricate heterojunctions composed of dissimilar materials with large mismatched lattice constants. We previously fabricated p-Si/n-GaAs and p-Si/n-SiC heterojunctions and investigated their electrical properties [3, 4]. It was found that the energy band diagram of p-Si/n-GaAs and p-Si/n-SiC junctions revealed type-II and type-I features, respectively. Furthermore, their conduction band discontinuities were calculated to be 0.59 and 0.3 eV, respectively. If SAB-based GaAs/SiC heterojunction are realized, the conduction band discontinuity of less than 0.3 eV should be expected, which should be suitable for fabricating devices with excellent high-frequency, high-temperature, and high-power performances that have not yet been achievable by each component material alone. In this work, we fabricated p+-GaAs/n-SiC heterojunction by using SAB method and have investigated the annealing temperature dependence of the band structure of GaAs/SiC heterojunction. The influence of the thermal annealing process on the electrical properties of the junctions were systematically investigated by measuring their current-voltage (I-V) and capacitance-voltage (C-V) characteristics. The applicability of GaAs/SiC heterojunctions for functional devices was explored based on these measurements. Experiments: p+-GaAs (100) epitaxial substrates (400 nm, ~ 1 × 1019 cm-3 epitaxial layer / substrate ~ 1 × 1018 cm-3) and n-4H-SiC epitaxial substrates (2.8 mm, 1.1 × 1017 cm-3 epitaxial layer / 0.5 mm, > 2 × 1018 cm-3 buffer layer / substrate ~ 1 × 1019 cm-3) were used for the bonding experiment. Before bonding Al/Ni/Au multilayers were evaporated on the backside of n-SiC substrates. The ohmic contacts of n-SiC substrates were formed by a rapid thermal annealing at 1000 °C for 60 s in N2 gas ambient. p+-GaAs epitaxial substrates and n-SiC epitaxial substrates were bonded to each other by using SAB [1, 2]. After the bonding, AuZn/Ti/Au multilayers were evaporated on the bottom surfaces of p-GaAs substrates. The p+-GaAs/n-SiC heterojunctions were annealed separately at 100, 200, 300, and 400 °C for 60 s in N2 gas ambient. All the samples were diced into 4 mm2 pieces. The characteristics of these samples were also investigated while the junction was unannealed. Their I-V and C-V characteristics were measured using an ADCMT 6242 Source Measurement Unit and an Agilent E4980A Precision Impedance Analyzer, respectively. Results: The 1/C2-V characteristics measured at room temperature and a frequency of 100 kHz are shown in Figure 1. The characteristics indicated a straight line and the flat-band voltages () were found to be 1.12, 1.12, 1.12, 1.13 and 1.29 V for the unannealed junction and junctions annealed at 100, 200, 300, and 400 °C, respectively, by linearly extrapolating 1/C2 to zero. It is noteworthy that the flat-band voltages remained constant as the annealing temperature increased up to 200 °C and then increased as the annealing temperature increased from 300 to 400 °C. Using the slopes of 1/C2-V characteristics, the donor concentrations of the n-SiC epitaxial layer were estimated to be 8.14 × 101 6, 8.02 × 1016, 7.98 × 1016, 7.93 × 1016, and 6.94 × 1016 cm-3, for the unannealed junction and junctions annealed at 100, 200, 300, and 400 °C, respectively, which are close to the norminal value of 1.1 × 1017 cm-3, as determined by Ni/n-SiC Schottky diode. Figure 1. C-V characteristics of p+-GaAs/n-SiC heterojunctions without being annealed and annealed at 100, 200, 300, and 400 °C measured at room temperature.

Growth of high quality N-polar n-GaN on vicinal C-face n-SiC substrates for vertical conducting devices

High quality N-polar n-type GaN films were deposited on vicinal C-face n-SiC substrates by metal organic chemical vapor deposition for vertical conducting devices. We employed the SiNx interlayer to N-polar GaN growth and studied the effect of SiNx interlayer on the properties of N-polar GaN. We found that the properties of N-polar films were greatly improved by using SiNx interlayer as characterized by X-ray diffraction, photoluminescence, and I-V measurements. N-polar n-type GaN films with SiNx interlayer exhibited a full width at half maximum of 422 arcsec for (0002) omega scan and 335 arcsec for (101¯2) omega scan, respectively. Integrated intensity ratio of near-band-edge emission and yellow-luminescence was increased by a factor of 4 by using SiNx interlayer. Besides, the resistance of the vertical structure with SiNx interlayer was reduced by 25% in comparison with that without SiNx interlayer.

Improved Vertical Isolation for Normally-Off High Voltage GaN-HFETs on n-SiC Substrates

Argon implantation of n-type SiC substrates prior to epitaxial growth of AlGaN/GaN HFETs stacks is used to decrease the vertical leakage to the conductive substrate. Normally-off p-GaN gate transistors with AlGaN-buffer and with iron-doped GaN-buffer were analyzed. The device OFF-state drain leakage was reduced for high drain voltages and the maximum breakdown strength was increased from 520 to 880 V for iron-doped GaN-buffer devices. Static device characteristics and the dynamic ON-state resistance of devices fabricated on pre-implanted SiC substrates are not degraded. High Resolution X-ray Diffraction (HRXRD) analysis confirms in coincidence that the GaN buffer defect density is not increased. Substrate implantation is thus beneficial for low-leakage high-voltage GaN devices on n-type SiC substrates.

Vertical conducting ultraviolet light-emitting diodes based on p-ZnO:As/n-GaN/n-SiC heterostructure

Vertical conducting light-emitting diodes based on p-ZnO/n-GaN structure were fabricated on conductive n-SiC(6H) substrates. The p-ZnO:As films were prepared by arsenic out-diffusion from a sandwiched GaAs interlayer on a GaN/SiC template, and the AsZn-2VZn complex was considered to be the most probable defect contributing to the p-type conductivity of the ZnO:As films. Under forward bias, an intense ultraviolet emission at ∼384 nm from the ZnO side was observed. The electroluminescence performance of the diode was remarkable in terms of its low emission onset and high-purity ultraviolet emission. Additionally, the unencapsulated diode showed good stability over a duration of 2 months.

Fast-Switching GaN-Based Lateral Power Schottky Barrier Diodes With Low Onset Voltage and Strong Reverse Blocking

GaN-based heterostructure lateral Schottky barrier diodes (SBDs) grown on n-SiC substrate are investigated in this letter. These SBDs own very low onset voltage V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</sub> = 0.43 V, high reverse blocking V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BR</sub> >; 1000 V, very low capacitive charge of 0.213 nC/A, and a very fast recovery time of 10 ps. These unique qualities are achieved by combining lateral topology, GaN:C back-barrier epitaxial structure, fully recessed Schottky anode (φ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> = 0.43 eV), and slanted anode field plate in a robust and innovative process. Diode operation at elevated temperature up to 200 °C was also characterized.

Photoelectrochemical etching to fabricate single-crystal SiC MEMS for harsh environments

In this paper, we report on a novel surface micromachining process technology for the fabrication of microelectromechanical systems in SiC. Single-crystal SiC suspended microstructures were fabricated using a dopant-selective photoelectrochemical etching process, which allows for undercutting the p-SiC layer by rapid lateral etching of the underlying n-SiC substrate. The selective etching was achieved by applying a bias which employs the different flat-band potentials of n-SiC and p-SiC in the KOH solution. Single-crystal SiC MEMS developed in this study fully exploits the superior mechanical and biocompatible properties of SiC and has the capability of monolithic integration with electron devices and circuits, and therefore, is promising for sensing and actuating operations in biomedical, high-temperature and harsh environments.

Study of Au/ZnO nanorods Schottky light-emitting diodes grown by low-temperature aqueous chemical method

High quality vertically aligned ZnO nanorods (NRs) were grown by low-temperature aqueous chemical technique on 4H-n-SiC substrates. Schottky light-emitting diodes (LEDs) were fabricated. The current-voltage (I–V) characteristics of Schottky diodes reveal good rectifying behavior. Optical properties of the ZnO nanorods (NRs) were probed by cathodoluminescence (CL) measurements at room temperature complemented with electroluminescence (EL). The room-temperature CL spectra of the ZnO NRs exhibit near band edge (NBE) emission as well as strong deep level emission (DLE) centered at 690 nm. At room temperature the CL spectra intensity of the DLE was enhanced with the increase of the electron beam penetration depth due to the increase of defect concentration at the interface and due to the conversion of self-absorbed UV emission. We observed a variation in the DLE along the nanorod depth. This indicates a relatively lower structural quality near the interface between ZnO NRs and n-SiC substrate. The room-temperature CL spectra of SiC show very weak emission, which confirms that most of the DLE is originating from the ZnO NRs, and SiC has a minute contribution to the emission.

Influence of Negative Charging on High Rate SiC Etching for GaN HEMT MMICs

We discuss the influence of negative charging on high-rate ICP etching of SiC via-holes for GaN HEMT MMICs. There is large differential etching behavior such as etch rate, etching profile, and RIE lag between S.I.- and n-SiC substrates because of the difference in wafer heating and negative charging of the sidewall during etching between both substrates. We analyze the difference in negative charging between both substrates by simulating the etching profile.

On-Resistance Modulation of High Voltage GaN HEMT on Sapphire Substrate Under High Applied Voltage

The 620-V/1.4-A GaN high-electron mobility transistors on sapphire substrate were fabricated and the ON-resistance modulations caused by current collapse phenomena were measured under high applied voltage. Since the fabricated devices had insulating substrates, no field-plate (FP) effect was expected and the ON-resistance increases of these devices were larger than those on an n-SiC substrate even with the same source-FP structure. The dual-FP structure, which was a combination of gate FP and source FP, was effective in suppressing the ON -resistance increase due to minimization of the gate-edge electric field concentration. The ON-resistance after the applied voltage of 250 V decreased by twice that at low drain voltage by the dual-FP structure. Gallium nitride (GaN), high-electron mobility transistor (HEMT), high voltage, power semiconductor device.

High Critical Electric Field Exceeding 8 MV/cm Measured Using an AlGaN p–i–n Vertical Conducting Diode on n-SiC Substrate

We have succeeded in obtaining the high critical electric field exceeding 8 MV/cm measured using an AlGaN p–i–n vertical conducting diode on n-SiC substrate grown by low-pressure metal organic vapor phase epitaxy. The critical electric field of AlGaN with Al composition of 57% is as high as 8.1 MV/cm, the highest among semiconductors with a doping concentration of less than 1017 cm-3, at which the avalanche multiplication process takes place. The critical electric field is proportional to the bandgap energy to a power of 2.7. In the forward current-voltage characteristics, the on-state resistance of the diode increases with increasing Al composition. Since there is a tradeoff between the breakdown voltage (VB) and the on-state resistance (Ron), the figure of merit VB2/Ron has its maximum when the Al composition is about 30% and is twice as high as that for GaN-based diodes. This indicates that AlGaN-based electronic devices are more promising for high-power operation than GaN-based ones.

Low-resistance graded Al xGa 1−xN buffer layers for vertical conducting devices on n-SiC substrates

We investigated the Al composition and thickness dependence of the resistance of graded Al x Ga 1− x N buffer layers for vertical conducting devices on n-type 6H-SiC substrates. To measure current–voltage characteristics, a Ti/Au ohmic contact was formed on the backside of the SiC substrate. The Al composition of the buffer layer was varied from 2% to 10%. We found that the optimal buffer layer thickness for the lowest resistance decreases with increasing Al composition because the nucleation seeds on SiC substrate coalesce faster. Since the optimal layer thickness depends on the Al composition, the sheet Al concentration, which is calculated from the Al composition and the thickness, should be considered as a critical parameter for low buffer resistance of vertical conducting devices on n-SiC substrates.

High critical electric field of AlxGa1−xN p-i-n vertical conducting diodes on n-SiC substrates

We report the current-voltage characteristics of AlxGa1−xN (x=0–0.22) p-i-n vertical conducting diodes grown on n-SiC substrates by low-pressure metal organic vapor phase epitaxy. An increase in the breakdown voltage was experimentally demonstrated with increasing Al composition. The corresponding critical electric fields were calculated to be 2.4MV∕cm for GaN and 3.5MV∕cm for Al0.22Ga0.78N. The critical electric field is proportional to the band gap energy to a power of 2.5. The forward voltage drop also increases with increasing Al composition but it is still as low as 5.2V even in the case of the Al0.22Ga0.78N p-i-n diode.

Observation of interface defects in thermally oxidized SiC using positron annihilation

Positron annihilation has been applied to study thermally oxidized 4H- and 6H-SiC. The SiC/SiO2 interface is found to contain a high density of open-volume defects. The positron trapping at the interface defects correlates with the charge of the interface determined by capacitance–voltage experiments. For oxides grown on n-SiC substrates, the positron annihilation characteristics at these defects are nearly indistinguishable from those of a silicon/oxide interface, with no discernable contribution from C-related bonds or carbon clusters. These results indicate that those defects at the SiC/oxide interface, which are visible to positrons, are similar to those at the Si/oxide interface. The positron annihilation characteristics suggest that these defects are vacancies surrounded by oxygen atoms.