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We report on the metastable defects introduced in the n-type 4H-SiC material by epithermal and fast neutron irradiation. The epithermal and fast neutron irradiation defects in 4H-SiC are much less explored compared to electron or proton irradiation-induced defects. In addition to the carbon vacancy (Vc), silicon vacancy (Vsi) and carbon antisite-carbon vacancy (CAV) complex, the neutron irradiation has introduced four deep-level defects, all arising from the metastable defect, the M-center. The metastable deep-level defects were investigated by deep level transient spectroscopy (DLTS), high-resolution Laplace DLTS (L-DLTS) and isothermal DLTS. The existence of the fourth deep-level defect, M4, recently observed in ion-implanted 4H-SiC, has been additionally confirmed in neutron-irradiated samples. The isothermal DLTS technique has been proven as a useful tool for studying the metastable defects.

We report on response of newly designed 4H-SiC Schottky barrier diode (SBD) detector to alpha, beta and gamma particles. In order to optimize SiC SBD detector’s thermal neutron efficiency, it’s of particular importance to understand its behavior in various radiation fields. The optimal size of the SBD is limited by degradation of electronic properties, and consequently their charge particle detection. We have manufactured diodes up to 3 x 3 mm active surface area to study those properties in correlation with increasing of detector size. Approximately 25 µm thick epitaxial layer is grown on SiC substrate by chemical vapor deposition, which is sufficient to stop alpha particles up to 6.8 MeV. Different active volume sizes of the detector based have been electrically characterized and exposed to radiation fields of alpha, beta and gamma particles. Extensive studies of the detector response to the various alpha emitters in the 3.27 MeV to 8.79 MeV energy range have been carried out. Results presented here demonstrate not only excellent linear response of the different detector active area to alpha particles, but also shows linear response to gamma particles. The detectors show a linear energy response, high charge collection efficiency and high energy resolution for the alpha particle energies bellow 6.7 MeV which is in a correlation with the range of charged particles in epitaxial layer of our detectors. Electrical characteristics of the detectors were assessed by temperature dependent current-voltage (I-V) and capacitance-voltage (C-V) measurements as well as by Laplace DLTS characterization of the electrically active defects. Ideality factor of the diodes is found to be in the range of 1.01 to 1.02 and free carrier concentration is in the range of 3x1014 cm-3 to 4.5x1014 cm-3. Co-60 and Cs-137 gamma radiations were carried out in Ruđer Bošković Institute’s Secondary Standard Dosimetry Laboratory with the air kerma rates up to 77 mGy/min., The 7th International Conference on Advancements in Nuclear Instrumentation Measurement Methods and their Applications (ANIMMA2021)

Pure and Al doped ZnO nanorods were prepared by a two-step chemical bath synthesis. The synthesis reposes on the deposition of a seed layer, i.e. spin coating of a thin-film of Zn solution on a silicon wafer in the first step, and on growing of the zincite nanorods (ZNRs), i.e. immersion of seed layer in an equimolar zinc nitrate and hexamethylenetetramine solution at elevated temperature for 1 h in the second step. For Al doped ZNRs the stoichiometry was adjusted by 3 at% of aluminium nitrate nonahydrate. The properties of the derived ZNRs and Al-doped-ZNRs thin-films were characterized by X-ray Diffraction (XRD), atomic force microscopy (AFM) and field emission gun scanning electron microscopy (FEG SEM) with energy dispersive X-ray spectroscopy (EDS). Structurally, the diffraction results point out to compositional differences of the nanorods as a result of the Al doping. Morphologic microscopy results are in concordance with diffraction data and additionally point out to a change in the geometry of the nanorods as a result of the Al doping. Electrical properties were examined by Kelvin probe force microscopy (KPFM) and by temperature-dependent current-voltage (I-V) measurements on Au/(Al)ZnO NR/n-Si junctions. The doping lead to an increase of conductivity of the ZnO NRs by an order of magnitude. The I-V characteristics for the pure and doped NRs follow the ohmic regime at lower voltages, while for the higher voltages the observed changes were attributed to the successful Al doping. The increase in the conductivity and shifting of the geometry of the nanorods can influence the overall electric transport properties which is a desirable behaviour in the area of photocatalysis and photovoltaics.

We present a study of electrically active radiation-induced defects formed in 4H-SiC epitaxial layers following irradiation with fast neutrons, as well as 600 keV H+ and 2 MeV He++ ion implantations. We also look at electron emission energies and mechanisms of the carbon vacancy in 4H-SiC by means of first-principles modelling. Combining the relative stability of carbon vacancies at different sites with the relative amplitude of the observed Laplace-DLTS peaks, we were able to connect Z1 and Z2 to emissions from double negatively charged carbon vacancies located at the h- and k-sites, respectively.

We present a study of deep level defects created in isolated ion cascades produced in nitrogen-low-doped 4H-SiC epitaxial layers by implantation of either accelerated H (600 keV) or He (2 MeV) ions using fast-scanning reduced-rate microbeams, in the so-called single ion regime. In the first DLTS measurement, defects labelled as ET2 (0.65 eV) and EH3 (1.06 eV) have been clearly distinguished from the presence of the dominant carbon vacancies (Z1/2 and EH6/7) in increased concentrations for irradiated samples. However, the second DLTS measurement revealed the almost complete removal of ET2 trap and the partial removal of EH3 trap, while the concentrations of Z1/2 and EH6/7 traps have further increased, due to the relatively low temperature annealing up to 700 K, accomplished during the first temperature scan of DLTS measurement. Since majority carrier concentration reduced after irradiation recovers with decreasing ET2 and EH3, those might act as majority carrier removal traps., 29th International Conference on Defects in Semiconductors (ICDS2017)

Silicij-karbid (SiC) je poluvodički materijal koji se intenzivno istražuje jer može podnijeti uvjete u kojima prevladavaju visoki iznosi temperature, električne snage, frekvencije i zračenja. Posebnu primjenu našao je u izradi poluvodičkih detektora. U ovom radu usporedili smo transportna svojstva SBD (Schottky barrier diode) detektora od silicija (Si) i 4H-SiC, koji imaju podjednaku dopiranost (n-tip, 10^14 cm-3). Korištena su temperaturno ovisna kapacitivno-naponska (C-V) i strujno-naponska (I-V) mjerenja na temperaturama od 100K do 380K. Pokazali smo da u gotovo svim svojstvima važnim za detektore SiC ima bolje karakteristike u odnosu na Si. Struja curenja, koja određuje minimalnu amplitudu signala u poluvodičkim detektorima, kod SiC je više od deset redova veličine manja nego kod Si. Promjena koncentracije slobodnih nosilaca naboja s temperaturom kod SiC je manja, što znači veću stabilnost i preciznost detektora. Povećanje faktora idealnosti sa spuštanjem temperature kod SiC je puno manje izraženo nego kod Si, i znak je da je zanemariva struja rekombinacije u području osiromašenja. To pokazuje da je mala koncentracija rekombinacijsko – generacijskih centara, što je posljedica izvrsne izrade analiziranog SiC uzorka, a omogućava dobru rezoluciju detektora. Detektor od SiC podvrgnuli smo neutronskom zračenju u TRIGA reaktoru na Institutu Jožef Štefan i zaključili da su transportna svojstva pokazala dobru otpornost s obzirom na primijenjene doze.

Ni/4H-SiC Schottky diode n-tipa ozračene su termalnim i brzim neutronima te implantirane s 2MeV He ionima. Zatim, izvršena je karakterizacija strujno-naponskim, kapacitivno-naponskim te mjerenjima tranzijentne spektroskopije dubokih nivoa. Ozračivanje termalnim neutronima u dozama do 1 x 1010 cm-2 nije uzrokovalo promjene karakteristika, što je u skladu s velikom otpornošću SiC na oštećenja pri ozračivanju. Ozračivanje brzim neutronima (pri dozi 1 x 1013 cm-2) je unijelo novi ET2 duboki nivo, dok se koncentracija Z1/2 dubokog nivoa povećala. Brzi neutroni energije oko 0.8 MeV (koji su korišteni u ovom radu) mogu unijeti samo vakancije i intersticije u SiC, stoga opaženi duboki nivoi su vezani uz njih. Kompenzacija je opažena pri dozi 1 x 1014 cm-2 brzih neutrona. Implantacija 2MeV He iona unijela je ET1, Z11/2 i ET2 duboke nivoe te uzrokovala kompenzaciju u području dosega 2MeV He iona u 4H-SiC. N-type Ni/4H-SiC Schottky diodes were irradiated by thermal and fast neutrons and implanted with 2MeV He ions. Afterwards, characterization by current-voltage, capacitance-voltage and deep level transient spectroscopy measurements was carried out. Irradiation with thermal neutrons at fluences up to 1 x 1010 cm-2 didn’t cause change of characteristics, which is in agreement with high radiation hardness of SiC. Irradiation with fast neutrons (fluence 1 x 1013 cm-2) has introduced a new ET2 deep level, while the concentration of Z1/2 has increased. Fast neutrons with an energy around 0.8 MeV (as used in this study) can introduce only vacancies and interstitials in SiC, so observed deep levels are related to them. Compensation was observed at fluence 1 x 1014 cm-2 of fast neutrons. Implantation of 2MeV He ions introduced ET1, Z1/2 and ET2 deep levels and caused compensation in the area of reach of 2MeV He ions.