Deep-Level Transient Spectroscopy and Radiation Detection Performance Studies on Neutron Irradiated 250-μm-Thick 4H-SiC Epitaxial Layers

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 10
¹⁰
–10
¹³
cm
⁻²
. Current–voltage (
I–V
) and capacitance–voltage (
C–V
) characteristics revealed that the detectors irradiated up to a fluence of 10
¹²
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 10
¹¹
cm
⁻²
, which broadened to 42 keV (0.8%) FWHM for a fluence of 10
¹²
cm
⁻²
.
I–V
and
C–V
measurements revealed substantial donor compensation in the epilayer irradiated at a fluence of ~10
¹³
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 10
¹⁰
cm
⁻²
revealed the formation of EH
₅
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 10
¹⁰
cm
⁻²
to
$2.6~\mu \text{m}$
at 10
¹²
cm
⁻²
indicating formation of hole-trap centers as well.