Absorption of terahertz radiation in Ge/Si(001) heterostructures with quantum dots

Abstract

The terahertz spectra of the dynamic conductivity and radiation absorption coefficient in germanium-silicon heterostructures with arrays of Ge hut clusters (quantum dots) have been measured for the first time in the frequency range of 0.3-1.2 THz at room temperature. It has been found that the effective dynamic conductivity and effective radiation absorption coefficient in the heterostructure due to the presence of germanium quantum dots in it are much larger than the respective quantities of both the bulk Ge single crystal and Ge/Si(001) without arrays of quantum dots. The possible microscopic mechanisms of the detected increase in the absorption in arrays of quantum dots have been discussed. DOI: 10.1134/S0021364010240033Artificial low-dimensional nanoobjects-quantum wells, quantum wires, and quantum dots-as well as structures based on them, are promising systems for improvement of existing devices and development of fundamentally new devices of micro and optoelectronics [1]. In addition to the necessity of the development of new technological processes and equipment for manufacturing nanostructures with required parameters, the investigation of the fundamental properties of such structures is also of primary importance. Size quantization of the energy of charge carriers whose spatial motion is limited at scales of about 100 nm or smaller is one of the most striking such properties. In particular, a quantum dot is a zero dimensional object can be considered as an artificial atom with one or more charge carriers (electrons or holes) having a discrete energy spectrum [2]. Arrays of a large number of quantum dots including multilayer heterostructures make it possible to form artificial "solids" whose properties can be controllably changed by varying the characteristics of constituent elements ("atoms") and the environment (semiconductor matrix). Such systems can have a very rich set of physical properties, which are caused by single-particle and collective interactions and depend on the number and mobility of carriers in quantum dots, Coulomb interaction between the carriers inside a quantum dot and in neighboring quantum dots, charge coupling between neighboring quantum dots, polaron and exciton effects, etc. These properties are actively studied during the last two decades. One of the main tools for such investigations is infrared spectroscopy, whose advantages are the contactless character of the measurements and the possibility of the direct observation of transitions between quantized energy states. The specificity of the infrared region is that almost all main interactions in low-dimensional nanostructures (distance between levels, Coulomb interaction between charges in quantum dots, one and multi-particle exciton and polaron effects, plasmon excitations) have the corresponding characteristic energies from several meV to 50-100 meV [3][4][5][6][7].It is worth noting that almost all performed infrared spectroscopy experiments were devoted to the measurement of the relative characteristics (e.g., relative tra...

Ge quantum dot arrays grown by ultrahigh vacuum molecular-beam epitaxy on the Si(001) surface: nucleation, morphology, and CMOS compatibility

“…From the capacitance-voltage characteristics of the samples with Ge/Si(001) heterostructures, the surface densities of holes in them were earlier estimated as 3.4 × 10 11 , 7.0 × 10 11 , and 1.7 × 10 11 cm −2 for h Ge = 6, 10, and 14 Å, respectively. These values almost coincide with the densities of the Ge clusters in arrays [51,52]. Notice also, that very high terahertz conductivity was observed by Zhukova et al [52] in the samples with h Ge = 8, 9, 10, and 14 Å which drastically decreased for h Ge = 18 Å and was not detected at all at 6 Å and lower values of h Ge .…”

“…These values almost coincide with the densities of the Ge clusters in arrays [51,52]. Notice also, that very high terahertz conductivity was observed by Zhukova et al [52] in the samples with h Ge = 8, 9, 10, and 14 Å which drastically decreased for h Ge = 18 Å and was not detected at all at 6 Å and lower values of h Ge .…”

Unfolding Band and Absorption Energy Shift of \(\text{Si-Ge}\) Nano Crystals from First-principles Calculations

“…The binary alloys of silicon (Si) and germanium (Ge), Si 1−x Ge x with x being the composition of Ge, have been of great interest in recent years thanks to their potential applications in manufacturing novel advanced opto-electronic devices [1][2][3][4][5][6][7]. With respect to thermoelectricity, the Si 1−x Ge x alloys have attracted much attention as energy harvesting materials.…”