Schottky barrier detectors on 4H-SiC n-type epitaxial layer for alpha particles

Schottky barrier detectors have been fabricated on 50 μm n-type 4H-SiC epitaxial layers grown on 360 μm SiC substrates by depositing ∼10 nm nickel contact. Current–voltage (I–V) and capacitance–voltage (C–V) measurements were carried out to investigate the Schottky barrier properties. The detectors were evaluated for alpha particle detection using a ²⁴¹Am alpha source. An energy resolution of ∼2.7% was obtained with a reverse bias of 100 V for 5.48 MeV alpha particles. The measured charge collection efficiency (CCE) was seen to vary as a function of bias voltage following a minority carrier diffusion model. Using this model, a diffusion length of∼3.5 μm for holes was numerically calculated from the CCE vs. bias voltage plot. Rise-time measurements of digitally recorded charge pulses for the 5.48 MeV alpha particles showed a presence of two sets of events having different rise-times at a higher bias of 200 V. A biparametric correlation scheme was successfully implemented for the first time to visualize the correlated pulse-height distribution of the events with different rise-times. Using the rise-time measurements and the biparametric plots, the observed variation of energy resolution with applied bias was explained.

Source:sciencedirect

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Ab initio theoretical and photoemission studies on formation of 4H-SiC(0 0 0 1)/SiO2 interface

Formation mechanisms of initial 4H-SiC (0 0 0 1)/SiO₂ interface were analyzed by density functional theory (DFT) and angle-dependent X-ray photoelectron spectroscopy (ADXPS). Through the theoretical model calculations, either C or O interstitial is likely to exist in the oxidation process of 4H-SiC. Besides, there is one suboxide theoretically more easily to form and more stable than any others. The results of the ADXPS experiment revealed only one suboxide with shift of +0.94 eV relative to the 4H-SiC bulk component rather than three ones, which verified the theoretical results. These calculation and experimental results demonstrated there is only one rather than three silicon suboxides that induced the high density of states in the 4H-SiC/SiO₂ interface. Besides, we did some speculations about the formation mechanism of the initial 4H-SiC/SiO₂ interface according to the theoretical and experimental results.

Highlights

• Either C or O interstitial is likely to exist in the oxidation process of 4H-SiC.

• One suboxide is more easily to form and more stable than any others.

• The experimental results of ADXPS support our theoretical calculations.

• We do speculations about the formation mechanism of initial 4H-SiC/SiO₂ interface.

Source: Applied Surface Science

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Effect of graphene/4H-SiC(0 0 0 1) interface on electrostatic properties in graphene

Electrostatic properties, quantum capacitance (Cq) and local density of states (LDOS) are evaluated for graphene on 4H-SiC(0 0 0 1) by measuring the local capacitance with Scanning Capacitance Spectroscopy (SCS). Two distinct samples were used for comparative study, viz., graphene exfoliated and deposited on 4H-SiC(0 0 0 1)—DG, and graphene grown epitaxially on 4H-SiC(0 0 0 1)—EG. We observed a distinctly lower screening length (rscr) and Cq while wider variations in the LDOS for EG. Such differences are attributed to the peculiar interface between EG/4H-SiC(0 0 0 1), which is known to be more or less defective having the presence of positive charges.

Research highlights

► Local electrostatic properties are evaluated for graphene on 4H-SiC(0 0 0 1).

► Lower screening length andCq are observed for epitaxial graphene on 4H-SiC(0 0 0 1).

► Such differences are attributed to the peculiar interface between EG/4H-SiC(0 0 0 1).

► The results are compared with graphene deposited on 4H-SiC(0 0 0 1).

Source: Physica E: Low-dimensional Systems and Nanostructures

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High resolution alpha particle detection using 4H–SiC epitaxial layers: Fabrication, characterization, and noise analysis

In this article we report the fabrication and characterization of large area, room-temperature operable and very high resolution Schottky barrier detectors for alpha particles using 20 μm thick n-type 4H–SiC epitaxial layers. Schottky barriers were fabricated by depositing circular nickel contacts of ~11 mm² area on the 4H–SiC epitaxial layers. Room temperature current–voltage measurements revealed very high Schottky barrier height of 1.6 eV and extremely low leakage current of 3.5 pA at an operating reverse bias of −90 V. We also report an energy resolution of 0.29%, which is the best resolution obtained so far for uncollimated 5.48 MeV alpha particles in 4H–SiC epitaxial detectors with such a large area. Very low micropipe density (<1 cm⁻²) and low effective doping concentration (2.4×10¹⁴ cm⁻³) in the epilayer helped to achieve a high resolution even with the large detector area and a broad source. A diffusion length of ~18.6 μm for holes has been determined in these detectors following a calculation based on a drift-diffusion model. A noise analysis in terms of equivalent noise charge revealed that the white series noise due to the detector capacitance has substantial effect on their spectroscopic performance.

Source:sciencedirect

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Heavily nitrogen-doped 4H-SiC homoepitaxial films grown on porous SiC substrates

Heavily nitrogen-doped 4H-SiC homoepitaxial films were grown on normal p-type and porous 4H-SiC (PSC) substrates. The nitrogen doping concentration and resistivity of the epitaxial films, measured by Hall measurement, were about 10²⁰–10²¹ cm⁻³ and 0.002–0.006 Ω cm, respectively. From X-ray analysis, it was observed that the crystallinity of the epilayer grown on porous 4H-SiC substrates is better than that grown on p-type 4H-SiC substrates. In spite of the heavy doping, the full-width at half-maximum (FWHM) value of the epitaxial film, which was grown on the porous substrate, was about 13 arcsec, proving its excellent crystal quality. In contrast, the heavily nitrogen-doped epilayer, which was grown on the normal substrate, had a FWHM value of 16.9 arcsec. High-voltage transmission electron microscope (HVTEM) and scanning electron microscope (SEM) observations made clear that the enhancement of the crystallinity was caused by stress relaxation near pore boundary and defect terminations in the porous layer.

Source: Journal of Crystal Growth

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Visible blind p+–π–n−–n+ ultraviolet photodetectors based on 4H–SiC homoepilayers

p⁺–π–n⁻–n⁺ ultraviolet photodetectors based on 4H–SiC homoepilayers have been presented. The growth of the 4H–SiC homoepilayers was carried out in a LPCVD system. The size of the active area of the photodetectors was 300×300 μm². The dark and illuminated I–V characteristics had been measured at reverse biases form 0 to 20 V at room temperature, and the illuminated current was at least two orders of magnitude than that of dark current below 13 V bias. The peak value zones of the photoresponse were located at 280–310 nm at different reverse biases, and the peak value located at 300 nm was 100 times greater than the cut-off response value in 380 nm at a bias of 10 V, which showed the device had good visible blind performance. A small red-shift about 5 nm on the peak responsivity occurred when reverse bias increased from 5 to 15 V.

Source:Microelectronics Journal

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Investigation of Single Crystal 4H SiC Growth by the Solvent-Laser Heated Floating Zone Technique

The solvent-laser heated floating zone (solvent-LHFZ) growth technique has been implemented to grow long single crystal silicon carbide (SiC) fibers. This technique combines the long fiber growth ability of laser heated floating zone with crystal growth by traveling solvent method's ability to grow single crystal SiC. This paper presents a complete look at the initial SiC growth study by solvent-LHFZ. This study shows that solvent-LHFZ readily grows single crystal SiC, growth rates are a function of both growth temperature and carbon concentration in the crystal growth source material, solvent incorporation is a function of carbon concentration in the crystal growth source material, and that an ordered growth front must be achieved in order to grow a long single crystal SiC fiber.
Highlights

• Solvent-Laser Heated Floating Zone developed to grow single crystal SiC fibers.

• Grown crystal retains 4H-SiC polytype and crystallographic direction.

• Crystal growth rates were found to be both a function of carbon concentration in the crystal growth source material and temperature.

• Solvent incorporation into the grown crystal is a function of carbon concentration in the crystal growth source material.

• Grown crystals have a significant amount of inhomogeneous strain caused by defects and solvent rich pockets of material trapped in the crystal.

• A more ordered growth front must be created before single crystal SiC fibers can be achieved.

Source:Journal of Crystal Growth

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Thermal conductivity evaluation of GaN–AlN–(4H)SiC hetero-epitaxial material system

In this work, the effective thermal conductivity of GaN–AlN–(4H)SiC hetero-epitaxial material system, is evaluated. The thermal conductivities of the bulk (substrate) Si, (4H)SiC, AlN, and GaN materials and the epitaxial-layers of the materials used in GaN–AlN–(4H)SiC hetero-epitaxial material system, are also evaluated using Callaway approach. It is observed that the GaN–AlN–(4H)SiC hetero-epitaxial material system has the effective thermal conductivity of approximately 2.0 W/cm K neglecting the (4H)SiC substrate and approximately 4.0 W/cm K, while considering the (4H)SiC substrate. Thus, this hetero-epitaxial material system is suitable to make semiconductor devices, not only for high-voltage, and high operation frequency, but also favorable for high temperature operation in comparison to the devices made up of discrete materials e.g., Si, (4H)SiC, and GaN.
Highlights.

► Effective thermal conductivity of GaN–AlN–(4H)SiC material system is evaluated.

► Callaway approach is made to know the thermal conductivities of the materials.

► Effective thermal conductivity of GaN–AlN–(4H)SiC is≅2.0 W/cm Kwithout (4H)SiC.

► Effective thermal conductivity of GaN–AlN–(4H)SiC is≅4.0 W/cm K with (4H)SiC.

► GaN–AlN–(4H)SiC is favorable for high frequency and high temperature operation.

Source:Solid State Communications

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Surface analysis and defect characterization of 4H–SiC wafers for power electronic device applications

4H–SiC wafers and epitaxial layers were analysed by optical microscopy, profilometer technique and scanning electron microscopy with the aim to evidence the defect morphology on large scale and to determine in both cases the different types of defects. A more detailed analysis has been performed by atomic force microscopy. Different types of defects such as micropipes, comets, super dislocations, etch pits and so on, have been characterized finding particular physical finger-prints. Electrical characterization performed on Schottky diodes realized on 4H–SiC wafers gave information about the correlation between defects and electrical performances of devices.

Source:Diamond and Related Materials

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