Temperature spectra of conductance of Ge/Si p-i-n structures with Ge quantum dots

Abstract This work presents results of investigation of Ge/Si p-i-n structures with Ge quantum dots in the i-region by the method of admittance spectroscopy. The structures contain multiple layers with Ge quantum dots separated by thin 5 nm layers of Si in the intrinsic region. Two peaks are observed on the temperature dependences of conductance of the investigated heterostructures. It is revealed that the second peak is broadened and corresponds to a system of closely lying energy levels

Peculiarities of the 7 × 7 to 5 × 5 Superstructure Transition during Epitaxial Growth of Germanium on Silicon (111) Surface

This paper presents the results of studying the processes of epitaxial growth of germanium on silicon with crystallographic orientation (111) in a wide temperature range. The temperature dependences of the duration of the transition stage from the 7 × 7 to 5 × 5 superstructure and the values of the critical thickness of the transition from two-dimensional to three-dimensional growth in the range from 250 to 700 °C are determined using the reflection high-energy electron diffraction method. It was shown for the first time that the transition time from the 7 × 7 superstructure to 5 × 5 superstructure depends on the temperature of epitaxial growth. The region of low temperatures of synthesis, which has received insufficient attention so far, is also considered

Molecular dynamics simulations of the growth of Ge on Si

The initial stages of the growth of germanium on the dimer reconstructed Si(100) surface is modelled using molecular dynamics (MD). Pyramidal island structures are observed to form despite MD being carried out at a deposition rate faster than experiment. By an examination of transitions that can occur from intermediate structures that form in the MD simulations, growth mechanisms can be identified. The initial wetting occurs as a result of Ge atoms diffusing into the trenches between the dimer rows. This results in Ge-Ge or Ge-Si dimer chains growing in rows perpendicular to the original Si-Si dimer rows on the surface. It is shown how strained Ge pyramids with square bases can form by diffusing atoms joining together adjacent dimer rows. From these initial square-based structures, complex concerted motions are observed in which atoms in lower layers ‘climb up’ to higher layers. Similar structures grown in the pure Si case exhibit much higher energy barriers for the ‘climbing up’ process indicating that the effect of strain is to reduce the energy barriers for pyramid formation. In addition to the investigation of atomistic growth processes, surface energy effects are also examined, which show that a germanium-covered Si(100) surface containing shallow-angled pyramids is energetically more favourable than that grown as a flat monolayer.</div

Admittance Investigation of MIS Structures with HgTe-Based Single Quantum Wells

This work presents results of the investigation of admittance of metal-insulator-semiconductor structure based on Hg(1 − x)Cd(x)Te grown by molecular beam epitaxy. The structure contains a single quantum well Hg(0.35)Cd(0.65)Te/HgTe/Hg(0.35)Cd(0.65)Te with thickness of 5.6 nm in the sub-surface layer of the semiconductor. Both the conductance-voltage and capacitance-voltage characteristics show strong oscillations when the metal-insulator-semiconductor (MIS) structure with a single quantum well based on HgTe is biased into the strong inversion mode. Also, oscillations on the voltage dependencies of differential resistance of the space charge region were observed. These oscillations were related to the recharging of quantum levels in HgTe

Thickness-dependent surface energy and formation of epitaxial quantum dots

© 2020 Elsevier B.V. Numerous theoretical and experimental studies show that during epitaxial growth according to the Stranski-Krastanow mechanism in systems mismatched by the lattice constant, the change in the surface energy of the system during nucleation and further growth of quantum dots, plays the most important role. In particular, this factor determines the equilibrium and critical thicknesses of the transition from two-dimensional to three-dimensional growth, and also affects other kinetic characteristics of the ensemble of nanoclusters, including the nucleation rate, surface density, and average size of the islands. Recent theoretical studies have made it possible to determine that the surface energy in this process depends on the thickness of the material deposited on the substrate. In this paper, we construct a kinetic model of the formation and coherent growth of two-dimensional layers and quantum dots in mismatched epitaxial systems, taking into account the dependence of the specific surface energies on the thickness of the deposited material. In this approximation, we calculate the basic parameters of the formed array of nanoislands. Experimental studies were also carried out on the growth of two-dimensional layers and quantum dots of germanium on the silicon (100) surface. The results of experimental investigations confirm the proposed theoretical model