Abstract
We report on efficient terahertz (THz) emission from high-electric-field-biased SiC structures with a natural superlattice at liquid helium temperatures. The emission spectrum demonstrates a single line, the maximum of which shifts linearly with increases in bias field. We attribute this emission to steady-state Bloch oscillations of electrons in the SiC natural superlattice. The properties of the THz emission agree fairly with the parameters of the Bloch oscillator regime, which have been proven by high-field electron transport studies of SiC structures with natural superlattices.
Highlights
The possibility of oscillating motion of electrons in crystals at high field bias has attracted great interest since it was predicted [1,2]
In accordance with the theory of Brillouin Zones (BZ) [16], the electron spectrum, for example, of the 6H-SiC crystal in the direction of the c-crystal axis should be considered in the extended BZ composed of six classical Brillouin zones of the crystal
An intensive THz signal was detected at bias voltages exceeding 190 to 195 V. The existence of such a threshold voltage for the THz emission can be explained by the impurity breakdown in the top n+-SiC layer, which is required for injection of electrons into the natural superlattice (NSL)
Summary
The possibility of oscillating motion of electrons in crystals at high field bias has attracted great interest since it was predicted [1,2]. The superperiodicity is absolutely stable and has precise crystalline parameters [14] This superperiodicity is self-organized in the main SiC crystal lattice, and the NSL periods, d, for such polytypes as 4H-, 6H-, and 8H-SiC are equal to 5, 7.5, and 10 A , respectively [14]. It was shown that the major energy breakups occur at 2π/c and 4π/c points for 6H-SiC [15], and at 2π/c, 4π/c, and 6π/c points for 8H-SiC, where c is the size of the elementary cell along the c-axis It explains the appearance of the NSL with the period d = c/2 and the miniband electron spectrum in hexagonal SiC polytypes
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