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(a) A schematic representation of the 4H-SiC crystal structure. The small and large disks represent C and Si atoms, respectively. There are two substitutional donor sites, cubic (k) and hexagonal (hex). (b) A schematic representation of the electron excitation and capture producing THz emission in 4H-SiC devices, showing the nitrogen donor cubic sites (left), and hexagonal sites (right). The processes are: (1) electron excitation at the donor site via impact ionization, (2) electron capture via emission of acoustic phonons, (3) radiative THz transitions between long-lived states and ground states, and (4) electron relaxation to via acoustic phonon emission.
(a) Top panel: THz emission spectrum of nitrogen doped 4H-SiC devices with a pumping current of 1 A at 4 K. Bottom panel: regular pattern of the FTIR interferogram corresponding to narrow emission peaks. (b) Evolution of the THz emission intensity with increasing pumping current at 4 K.
(a) Top: THz emission spectrum of nitrogen doped 4H-SiC devices with a pumping current of 2 A at 80 K. Bottom panel: regular pattern of the corresponding interferogram. (b) Evolution of the THz emission spectra with a pumping current of 2 A.
(Color online) Light output vs current (red dashed lines) and (black solid lines) characteristics of a typical device at 4 and 80 K. The equivalent peak power is determined from the measured average power divided by the duty cycle of the electrical pulses.
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