SiC Natural Superlattices Research Articles

SiC Natural and Artificial Superlattices for the Implementation of the Bloch Oscillation Process: A Comparative Analysis

Bloch oscillations in semiconductors have been studied for several decades. Oscillations were observed in artificial superlattices based on AlGaAs-GaAs proposed Esaki and Tsu, and the natural superlattice based on superstructures SiC. In this paper we considers some base properties of the SiC natural superlattices that are the ground for the Bloch oscillations existence in these materials and attract attention to the some main disadvantages of the artificial superlattices. The experimental detection of the Bloch oscillation-dependent physical effects in semiconductors has been an actual problem over decades.

Terahertz Emission from SiC Natural Superlattices in Strong Electrical Field

Terahertz electroluminescence of unipolar n⁺⁺-n⁻-n⁺ SiC structures at helium temperatures and I-V characteristics of bipolar n⁺⁺-π-n⁺ SiC structures with natural superlattices at 300~K at strong electrical fields are studied. The properties of the THz electroluminescence and I-V characteristics testify that these phenomena due to Bloch oscillations.

Simulation of a Terahertz Laser in the Bloch Oscillation Mode

Possible designs of a terahertz laser that use the effect of Bloch oscillations in SiC natural superlattices have been considered. It has been proposed to use as a resonator the SiC crystal itself on which the active layer was grown. The sizes of resonators for strip and whispering gallery mode lasers have been calculated. The advantages of a resonator with whispering gallery modes have been shown.

THz Emission from SiC Natural Superlattice Diodes Induced by Strong Electrical Field

Recently the intense terahertz electroluminescence from monopolar n++–n– –n+ structures of 6H- and 8H-SiC of natural superlattices at helium temperatures due to Bloch oscillations was discovered. In the present work we present the THz emission spectra of bipolar n++–π–n+ structures (π is a high-resistance layer of p-type conductivity) of natural superlattices 4H-, 8H- and 15R-SiC at 7 K. The bipolar n++–π–n+ structures of 4H- and 8H-SiC were analogous to those of structures for which the negative differential conductivity effect was observed earlier for three polytypes (4H, 6H and 8H) at T=300 K. We demonstrate resemblance and differences of the spontaneous THz emission spectra for the monopolar and bipolar 4H-, 6H- 8H- and 15R-SiC natural superlattices caused by Bloch oscillations of electrons in the SiC natural superlattice.

Расчет терагерцевого лазера в режиме блоховских осцилляций

AbstractPossible designs of a terahertz laser that use the effect of Bloch oscillations in SiC natural superlattices have been considered. It has been proposed to use as a resonator the SiC crystal itself on which the active layer was grown. The sizes of resonators for strip and whispering gallery mode lasers have been calculated. The advantages of a resonator with whispering gallery modes have been shown.

New Efficient Canal of THz Emission from SiC Natural Superlattices in Conditions of Wannier-Stark Localization

The comprehensive study of the terahertz electroluminescence caused by the Bloch oscillations of the electrons in the natural superlattices of 8H-, 6H-SiC with strong electrical field applied along the natural superlattices axis is represented. The electroluminescence spectra become much broader when the bias field exceeds substantially the threshold field of the Bloch oscillations. This spectral broadening can be explained by an appearance of a new spectral line that is much wider and its maximum is localized at higher energy than lines induced by Bloch oscillations. This line has no link with the Bloch oscillations mechanism and it is a result of the presumed changes in the SiC conduction band with complex electron spectrum structure by applied electrical field.

Terahertz emission from SiC natural superlattices in strong electrical field

Results are reported from a study of the terahertz electroluminescence from 8H-, 6H-, and 4H-SiC natural superlattices under the action of an electrical field applied along the natural superlattice axis. It is shown that the single, relatively narrow emission lines (L1-lines) dominate in the electroluminescence spectrum at moderate bias voltages and follow the increase of the width of the first mini-band of the superlattice in accordance with the criterion for Bloch oscillations. At bias voltages well above the Bloch oscillation threshold, the structure of the terahertz emission spectra undergoes considerable changes, which occur due to the appearance of a new intense, broader emission line (L2-line) with a maximum at about 12–13 meV. Tentatively, this latter emission is attributed to optical transitions between Wannier-Stark ladders formed from degenerate states in a side minimum of the SiC conduction band under strong electric field conditions.

The intensive terahertz electroluminescence induced by Bloch oscillations in SiC natural superlattices

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.

Terahertz Electroluminescence of 6H-SiC Natural SiC Superlattice in Bloch Oscillations Regime

We report on efficient terahertz emission in the region of 1.5-2 THz from high electric field biased 6H-SiC structures with a natural superlattice at liquid helium temperatures. The shape of the emission spectrum, the linear dependence of its maximum on the bias and the characteristic field strength required to achieve the emission allow the emission to be attributed to steady-state Bloch oscillations of electrons in the SiC natural superlattice.