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In this article, we demonstrate the radiation detection performance of vertical metal-oxide-semiconductor (MOS) capacitors fabricated on 20 μm thick n-4H-SiC epitaxial layers with the highest energy resolution ever reported. The 100 nm SiO2 layer was achieved on the Si face of n-4H-SiC epilayers using dry oxidation in air. The Ni/SiO2/n-4H-SiC MOS detectors not only demonstrated an excellent energy resolution of 0.42% (Δ E / E × 100) for 5.48 MeV alpha particles but also caused a lower enhancement in the electronic noise components of the spectrometer compared with that observed for the best high-resolution Schottky barrier detectors. The MOS detectors also exhibited a high charge collection efficiency (CCE) of 96% at the optimized operating bias despite the presence of the oxide layer. A drift-diffusion model applied to the CCE vs gate bias voltage data revealed a minority (hole) carrier diffusion length of 24 μm. Capacitance mode deep level transient spectroscopy (C-DLTS) scans in the temperature range 84–800 K were carried out to identify the resolution limiting electrically active defects. Interestingly, the C-DLTS spectra revealed both positive and negative peaks, indicating the simultaneous presence of electron (majority) and hole (minority) trap centers. It has been inferred that at the steady-state bias for the C-DLTS measurement, the MOS detector operates in the inversion mode at certain device temperatures, causing holes to populate the minority trap centers and, hence, manifests minority carrier peaks as well. [ABSTRACT FROM AUTHOR]

We report the fabrication of novel self-biased high resolution radiation detectors achieved in n-type 4H-SiC metal-oxide-semiconductor (MOS) devices. Vertical MOS structure has been realized by pulsed laser deposition of 40 nm Y2O3 layer on 20 $\mu \text{m}$ n-type 4H-SiC epilayer followed by sputter coating a nickel gate, which revealed a record-high hole diffusion length. The MOS device exhibited a remarkable radiation detection response to 5486 keV alpha particles with a charge collection efficiency of 82% and an energy resolution of 72 keV full width at half maximum (FWHM) at zero applied bias. The hole diffusion length has been calculated to be 56 $\mu \text{m}$ using a drift-diffusion model. Such long hole diffusion length and a flat-band potential of 2.1 V, enabled to attain high efficiency and resolution in the self-biased mode. Band energy calculations indicated that the presence of Y2O3 layer may have neutralized the hole traps usually present in a metal-4H-SiC interface thereby substantially improving the hole transport. Such high performing self-biased radiation detectors fabricated on 4H-SiC are intended for applications in harsh environment space missions, wherein carrying detector power supplies as a payload becomes a critical logistic issue. The present study opens the high potential of other wide bandgap semiconductors as self-biased MOS devices as well. [ABSTRACT FROM AUTHOR]

We report the fabrication of vertical metal–oxide–semiconductor (MOS) detectors with the highest energy resolution ever reported. The MOS detectors have been fabricated on 50- $\mu \text{m}$ -thick n-type 4H-SiC epitaxial layers by growing a silicon dioxide (SiO2) layer thermally prior to contact deposition. The MOS detectors exhibited leakage currents two orders of magnitude lower than that observed in a Schottky barrier detector (SBD) fabricated on similar 4H-SiC epilayers. The MOS detectors exhibited a much higher energy resolution of 0.4% compared to 0.8% observed in an SBD for 5486-keV alpha particles although both the devices showed a high charge collection efficiency (CCE) of 96% when exposed to the alpha particles. Capacitance mode deep-level transient spectroscopy (C-DLTS) revealed the presence of “lifetime killer” $\text{Z}_{\mathrm {1/2}}$ defects in similar concentrations in both the devices, and however, the corresponding capture cross section in the SBD has been observed to be one order of magnitude higher compared to the MOS detector, and instead of EH6/7 center seen in the SBD, the MOS device showed the presence of EH5 center. The higher resolution of the MOS device is attributed to the lower leakage current and difference in defect configurations observed between the two devices. The MOS detector showed a positive polarity C-DLTS peak with an activation energy of 1.22 eV, which is likely due to the nonnegligible impedance of the back contact because of the SiO2 layer. The present study opens the great potential of other wide bandgap semiconductor-based vertical MOS detectors, which can be fully depleted for high-resolution X-/ $\gamma $ -ray detection. [ABSTRACT FROM AUTHOR]

The effect of super-cadmium neutron-induced defects on radiation detection performance of Schottky barrier diodes, fabricated on 250- $\mu \text{m}$ -thick 4H-SiC epitaxial layers with ultralow intrinsic defect concentration, has been studied. The epilayers were irradiated in a TRIGA Mark II nuclear reactor dry instrumentation tube [intrareflector irradiation system or (IRIS)] in the net neutron fluence range 1010–1013 cm−2. Current–voltage (I–V) and capacitance–voltage (C–V) characteristics revealed that the detectors irradiated up to a fluence of 1012 cm−2 maintained a Schottky diode behavior. Radiation detection measurements showed an energy resolution of 28 keV (0.5%) full-width at half-maximum (FWHM) when exposed to 5486-keV alpha particles for the epilayers irradiated up to a neutron fluence of 1011 cm−2, which broadened to 42 keV (0.8%) FWHM for a fluence of 1012 cm−2. I–V and C–V measurements revealed substantial donor compensation in the epilayer irradiated at a fluence of ~1013 cm−2; however, the detector still worked satisfactorily with an energy resolution of 76-keV (1.8%) FWHM. The degradation in the detector performance with increased neutron dose was attributed to the trapping of charge carriers in the radiation-induced trap centers. Deep-level transient spectroscopy studies in the detector irradiated with a fluence of 1010 cm−2 revealed the formation of EH5 centers along with an unidentified deep electron trap located at 1.8 eV below the conduction band edge, both usually absent in as-grown 250- $\mu \text{m}$ 4H-SiC epilayers. A drift-diffusion model of charge transport showed a degradation in hole diffusion length from 10 $\mu \text{m}$ at a neutron fluence of 1010 cm−2 to $2.6~\mu \text{m}$ at 1012 cm−2 indicating formation of hole-trap centers as well. [ABSTRACT FROM AUTHOR]

We report the effect of EH6/7 electron trap centers alone on the performance of high-resolution radiation detectors fabricated on n-type 4H–SiC epitaxial layers. A Schottky barrier detector (SBD) and a metal-oxide-semiconductor (MOS) capacitor detector fabricated using two sister samples derived from the same 50 μm 4H–SiC parent wafer exhibited widely different energy resolutions of 0.4% and 0.9% for 5486 keV alpha particles. An equivalent noise charge model analysis ruled out the effect of the detector capacitance and the leakage current on the resolution of the detectors. Deep level transient spectroscopic studies revealed the presence of two trapping centers in each detector within the temperature scan range 240–800 K. The Z1/2 center, a potential electron trap, was detected in both the detectors in equal concentration, which suggested that the observed difference in the energy resolution is due to the presence of the other defect, the EH6/7 center, in the SBD. The capture cross section of the EH6/7 center was calculated to be three orders of magnitude higher than the second defect [a carbon antisite vacancy (CAV) center] observed in the MOS detector with an activation energy of 1.10 eV, which accounted for the enhanced electronic trapping in the SBD leading to its poor energy resolution. It has been proposed that the EH6/7 centers in the SBD have likely been reconfigured to CAV pairs during the thermal growth of the silicon dioxide layer in the MOS detector. The proposed formation mechanism of CAV, a stable qubit state for quantum information processing, addresses the outstanding questions related to the role of defect dynamics in their formation. [ABSTRACT FROM AUTHOR]

In this letter we investigate for the first time the behavioral differences of transport properties of electrons and holes observed in high-resolution radiation detectors fabricated on high-purity single crystalline diamond using biparametric (BP) correlation studies. The chemical vapor deposition (CVD) grown $500~\mu \text{m}$ thick diamonds exhibited an excellent energy resolution of 0.5% for 5486 keV alpha particles for both electron and hole transport in a vertical electrode geometry. Interestingly, the behavior of the electron and hole transport were found to be vastly different at bias voltages less than 100 V. No discernable detector signal was observed due to electron transit below an applied bias of −100 V. The hole transit on the other hand, resulted in resolvable pulse height spectrum (PHS) from bias voltages as low as +10 V. Digital biparametric correlation studies of the rise-times and induced charge from each interaction of the incident alpha particles, revealed that the observed difference is due to the excessive electron trapping below bias voltages of −100 V. At lower biases, the width of the alpha peak in the PHS due to hole movement, was hardly affected by trapping and was observed to be limited due to lower hole drift velocities. The developed method with new insights of correlating the biparametric plots and the detector performance can be extended to vast range of semiconductor detectors. [ABSTRACT FROM AUTHOR]

• The influence of SiO 2 growth conditions for 4H-SiC metal-oxide-semiconductor (MOS) radiation detectors have been reported. • MOS capacitors fabricated on 4H-SiC using oxygen enriched growth exhibited lower dark currents compared to in-air growth. • Detectors prepared using both the methods exhibited very high energy resolution, FWHM ≤ 0.5%, for 5486 keV alpha particles. • Capacitance mode deep level transient spectroscopic (DLTS) studies revealed electron traps such as Z 1/2 and EH 5 defects. • The DLTS scans also revealed minority trap related peaks. High resolution radiation detection has been demonstrated using Ni/SiO 2 /n-4H-SiC metal-oxidesemiconductor vertical capacitors fabricated using highly crystalline 4H-SiC epilayers. The oxide layers have been grown thermally using two different approaches: i) in-air, and ii) oxygen-ambience oxidation. The devices fabricated using the former method exhibited dark currents one order of magnitude higher than that in the latter. The observed difference has been attributed to the back-contact series resistance and capacitance. Regardless of the difference in the device parameters, detectors prepared using both of the methods exhibited very high energy resolutions of ≤ 0.5% for 5486 keV alpha particles emitted by an 241Am radioisotope. Capacitance mode deep level transient spectroscopic (DLTS) studies revealed similar type of electrically active defects along with Z 1/2 and EH 5 deep level defects in both the types of devices. The DLTS scans also revealed positive polarity peaks in these devices which indicate emission from minority carrier trap centers. The activation energy corresponding to the peak was found to be ∼1.2 eV which has been assigned to HK3 defects responsible for hole trapping in 4H-SiC. The possibility of appearance of the positive peak due to non-negligible impedance of the back-contact has been ruled out based on the observation that the centroid of the observed peak did not change with detectors having different device parameters. [ABSTRACT FROM AUTHOR]

• Crystal growth of CZTS crystals using a vertical gradient freeze (VGF) method. • Significant reduction in crystal growth duration. • 100 % charge collection efficiency has been obtained for 5486 keV alpha particles. • Significant improvement in electron drift mobility and mobility-lifetime product. We report the growth of detector grade Cd 0.9 Zn 0.1 Te 0.97 Se 0.03 (CZTS) single crystals, a recently discovered quaternary semiconductor for room temperature radiation detection, by a vertical gradient freeze (VGF) method. VGF is a comparatively low-temperature growth method and avoids relative motion between the heater and the ampoule containing the precursor materials which minimizes any thermal drift or temperature fluctuations. As a result, CZTS single crystals with superior charge transport properties has been obtained. Growth of detector-grade CZTS single crystals using VGF method has not been reported yet. X-ray spectroscopy based elemental analysis showed that the grown crystals demonstrated the desired stoichiometry required for high resolution radiation detection. Planar detectors fabricated by deposition of gold contacts (∼0.07 cm2) demonstrated high bulk resistivity ∼1010 Ω-cm and a very low leakage current density of 2.8 × 10−8 A/cm2 at a bias of 100 V when measured at room temperature. The detectors showed excellent radiation response with 100 % charge collection efficiency when exposed to 5486 keV alpha particles. The electron mobility-lifetime (μ τ) product was measured to be 3 × 10−3 cm2/V using a single polarity Hecht analysis which is at par with the recently reported values measured in CZTS grown using conventional Bridgman or travelling heater method. The electron mobility has been calculated to be 964 cm2V−1s−1 using a time-of-flight (TOF) method, a substantial improvement over that obtained from conventionally grown CZTS single crystals. [ABSTRACT FROM AUTHOR]