4H-SiC Detectors Research Articles

Performance of a 4H-SiC Schottky diode as a compact sized detector for neutron pulse form measurements

4H-silicon carbide (4H-SiC) detectors are desirable for neutron pulse form measurement for their compact size, excellent radiation resistance and hydrogen free composition. The aim of this study is to investigate the use of a 4H-SiC detector to measure the pulse form of a neutron burst. A 4H-SiC detector is fabricated and tested in the pulsed neutron field of the Chinese Fast Burst Reactor II (CFBR II). Important parameters such as the breeding period and the FWHM of the neutron pulse are derived from the experimental result of the 4H-SiC detector. These parameters agree well with those from a plastic scintillator detector. The divergences are only 0.5%, demonstrating that the 4H-SiC detector can yield a high fidelity time profile of the CFBR II pulse. The difference in peak centroid of alpha spectra is negligible for the 4H-SiC detector even after 18 reactor pulses (a neutron fluence of 8.41×1012cm−2), confirming the excellent radiation hardness of the 4H-SiC detector in pulsed neutron field. This study therefore indicates that 4H-SiC detectors can be usable as a compact sized detector to measure neutron pulses.

Simulation of near-infrared photodiode detectors based on β-FeSi2/4H-SiC heterojunctions

In this paper, we propose a near-infrared p-type β-FeSi2/n-type 4H-SiC heterojunction photodetector with semiconducting silicide (β-FeSi2) as the active region for the first time. The optoelectronic characteristics of the photodetector are simulated using a commercial simulator at room temperature. The results show that the photodetector has a good rectifying character and a good response to near-infrared light. Interface states should be minimized to obtain a lower reverse leakage current. The response spectrum of the β-FeSi2/4H-SiC detector, which consists of a p-type β-FeSi2 absorption layer with a doping concentration of 1 × 1015 cm−3 and a thickness of 2.5 μm, has a peak of 755 mA/W at 1.42 μm. The illumination of the SiC side obtains a higher responsivity than that of the β-FeSi2 side. The results illustrate that the β-FeSi2/4H-SiC heterojunction can be used as a near-infrared photodetector compatible with near-infrared optically-activated SiC-based power switching devices.

Characterization of 4H-SiC Epitaxial Layers and High-Resistivity Bulk Crystals for Radiation Detectors

Defect and electrical characterization of bulk semi-insulating (SI) 4H-SiC crystals and SI and n-type 4H-SiC epitaxial layers grown by chemical vapor deposition (CVD) on highly doped (0001) 4H-SiC substrates is reported. Optical microscopy, electron beam induced current (EBIC) imaging, current-voltage ( $I$ – $V$ ) measurements, thermally stimulated current (TSC) spectroscopy (94 K–620 K), Hall effect, and van der Pauw measurements have been conducted for characterization and defect correlation studies. Both epitaxial layers exhibited relatively shallow levels related to Al, B, $L$ - and D-centers. Deep level centers in the n-type epitaxial layer peaked at ${\sim} 400$ K ( $E_{a} \sim 1.1$ eV), and ${\sim} 470$ K were correlated with $IL_{2}$ defect and 1.1 eV center in high-purity bulk SI 4H-SiC. The SI epitaxial layer exhibited peak at ${\sim} 290$ K ( $E_{a} = 0.82\hbox{--}0.87$ eV) that was attributed to $IL_{1}$ and HK2 centers, and at ${\sim} 525$ K that was related to intrinsic defects and their complexes with energy levels close to the middle of the band-gap. Results of EBIC and optical microscopy showed segregation of threading dislocations around comet tail defects in the n-type epitaxial layer. The $I$ – $V$ characteristics of the devices on SI epitaxial layer exhibited steps corresponding to the ultimate trap filling of deep centers. The high-temperature resistivity measurements of bulk SI 4H-SiC sample revealed resistivity hysteresis that was attributed to the filling of the deep-level electron trap centers. The responsivity of the n-type epitaxial 4H-SiC detector in the soft X-ray energy range is reported for the first time.

Charge transport in 4H-SiC detector structures under conditions of a high electric field

Transport of nonequilibrium charge packets in a structure with a Schottky barrier fabricated on a CVD-grown n-4H-SiC film has been studied at the maximum strength of an electric field at 1.1 MV/cm. The charge was introduced by separate α-particles and recorded by nuclear spectrometric techniques. A superlinear rise in the recorded charge as a function of the reverse bias applied to the structure was observed. Simultaneously, and also superlinearly increased the scatter in the spectrum of the charge amplitude. The observed effect is attributed to the initial stage of impact ionization. The manifestation of the process at unconventionally low fields (∼1 MV/cm) is accounted for by specific features of the process of charge generation. Carriers generated by slowing-down α-particles are “hot” from the very beginning.

Charge collection efficiency mapping of interdigitated 4H–SiC detectors

The Ion Beam Induced Charge (IBIC) technique was used to map the charge collection efficiency (CCE) of a 4H–SiC photodetector with coplanar interdigitated Schottky barrier electrodes and a common ohmic contact on the back side. IBIC maps were obtained using focused proton beams with energies of 0.9 and 1.5 MeV, at different bias voltages and different sensitive electrode configurations (charge collection at the top Schottky or at the back Ohmic contact). These different experimental conditions have been modeled using a two-dimensional finite element code to solve the adjoint carrier continuity equations and the results obtained have been compared with experimental results. The excellent agreement between the simulated and experimental CCE maps allows an exhaustive interpretation of the charge collection mechanisms occurring in pixellated or strip detectors.

Charge transfer in the presence of a layer of trapping centers in semiconductor SiC ionizing radiation detectors

The formation of a response signal in the presence of a layer of trapping centers in semiconductor SiC ionizing radiation detectors is considered on the basis of a new model. Since the trapping layer is situated near the detector surface, nuclear particles that possess long tracks partly generate a charge behind this layer. Under certain conditions, the proposed model leads to a paradoxical situation, in which the signal decreases with increasing bias voltage. The application of the model to results obtained using ion-doped 4H-SiC detectors provides a qualitative explanation for the experimentally observed increase in the signal with the temperature in the region of saturation with respect to the bias voltage (i.e., under the conditions of total charge transfer), which were previously unclear.

Silicon carbide for UV, alpha, beta and X-ray detectors: Results and perspectives

Silicon carbide (SiC) is one of the candidates for the next generation semiconductor materials. Due to the wide bandgap (4H-SiC 3.2 eV), high critical breakdown voltage, high saturated drift velocity, high thermal conductivity, the detector fabricated with SiC has very low dark current, significantly high operating temperature and for UV sensors, insensitivity to visible/IR backgrounds compared to conventional Si detectors. In this paper, recent results on UV, alpha, beta and X-ray 4H-SiC detectors will be presented. High-energy resolution and full charge collection efficiency (CCE) have successfully been demonstrated before irradiation. After irradiation, the alpha and beta detectors continue to be operative, with a high CCE until fluences of the order of some 10 14 n/cm 2. The results for UV detectors show that the 4H-SiC photodetectors are capable of operating as solar-blind UV detector. SiC pixel detectors show leakage currents of a few femptoamperes at room temperature, which means a noise contribution of less than 1 e − r.m.s. High performance for X-ray can be achieved with SiC detectors even above room temperature without using any cooling system.

The effect of irradiation with high-energy protons on 4H-SiC detectors

The effect of irradiation of 4H-SiC ionizing-radiation detectors with various doses (as high as 1016 cm−2) of 24-GeV protons is studied. Isotopes of B, Be, Li, He, and H were produced in the nuclear spallation reactions of protons with carbon. Isotopes of Al, Mg, Na, Ne, F, O, and N were produced in the reactions of protons with silicon. The total amount of the produced stable isotopes varied in proportion with the radiation dose from 1.2 × 1011 to 5.9 × 1013 cm−2. It is shown that, at high radiation doses, the contact characteristics of the detectors change appreciably. The potential-barrier height increased from the initial value of 0.7–0.75 eV to 0.85 eV; the rectifying characteristics of the Schottky contacts deteriorated appreciably. These effects are attributed to the formation of a disordered structure of the material as a result of irradiation.