  Silicon-based fast time detectors have been widely used in high energy
physics, nuclear physics, space exploration and other fields in recent years.
However, silicon detectors often require complex low-temperature systems when
operating in irradiation environment, and their detection performance decrease
with the increase of irradiation dose. Compared with silicon, silicon carbide
(SiC) has a wider bandgap, higher atomic displacement energy, saturated
electron drift velocity and thermal conductivity. Simultaneously, the low gain
avalanche detector avoids crosstalk and high noise from high multiplication due
to its moderate gain, and thus can maintain a high detector signal without
increasing noise. Thus, the 4H-SiC particle detector, especially the low gain
avalanche detector has the potential to detect the minimal ionized particles
(MIPs) under extreme irradiation and high temperature environments. In this
work, the emphasis was placed on the design of a 4H-SiC Low Gain Avalanche
Detector (LGAD), especially the epitaxial structure and technical process which
played the main roles. In addition, a simulation tool--RASER(RAdiation
SEmiconductoR) was developed to simulate the performances including the
electrical properties and time resolution of the 4H-SiC LGAD we proposed. The
working voltage and gain effectiveness of the LGAD were verified by the
simulation of electrical performances. The time resolution of the LGAD is (35.0
$\pm$ 0.2) ps under the electrical field of -800 V, which is better than that
of the 4H-SiC PIN detector.
