Miniband-related 1.4–1.8 μm luminescence of Ge/Si quantum dot superlattices

Abstract

The luminescence properties of highly strained, Sb-doped Ge/Si multi-layer heterostructures with incorporated Ge quantum dots (QDs) are studied. Calculations of the electronic band structure and luminescence measurements prove the existence of an electron miniband within the columns of the QDs. Miniband formation results in a conversion of the indirect to a quasi-direct excitons takes place. The optical transitions between electron states within the miniband and hole states within QDs are responsible for an intense luminescence in the 1.4-1.8 lm range, which is maintained up to room temperature. At 300 K, a light emitting diode based on such Ge/Si QD superlattices demonstrates an external quantum efficiency of 0.04% at a wavelength of 1.55 lm.

10.1007/s11453-008-3011-8

“…The E1 peak shifted from 170 to 125 K as U r was changed from 1.3 to 11.0 V. For the same U r , the E3 peak shifted from 286 to 190 K and E2 peak from 235 to 140 K. Using the Arrhenius plot and a simulation method based on the fitting of the theoretical curve for the DLTS signal to the measured one, we have estimated the electron thermal activation energies for the E1-E3 levels; for U r = 5.28 V they appeared to be equal to ~250, 185, and 160 meV, respectively. These energies are substantially higher than the value of the conduction band offset at the Ge/Si heterointerface, which was found in [3,4] to be equal to 110 meV, and the electron activation energies of 55-65 meV for the SL levels.…”

“…A possibility of observing the Wannier-Stark effect in SLs consisting of QDs was noted in the theoretical study [9]. When studying the photoluminescence of a 20-layer p -n heterostructure with Ge/Si QDs obtained by molecular beam epitaxy, we have found [2][3][4] that a multimodal periodic structure is observed in the spectra, which reflects the distribution of the wave function squared for the states of the Wannier-Stark ladder. Observation of the Wannier-Stark ladder becomes possible in the case where the multilayer heterostructure is a Ge/Si QD superlattice (QDSL) with degeneracy of the miniband energies lifted by the builtin electric field of the p -n junction.…”

“…To overcome low quantum efficiency of Si-based optoelectronic devices, attempts were made to obtain Si-based nanostructures with a direct band structure. Multilayer heterostructures with Ge/Si quantum dots (QDs) are among these structures; in the case of thin Si layers between Ge QDs, these multilayer heterostructures can form Ge/Si superlattices (SLs) [1][2][3][4]. The electron wave functions in these SLs can be completely delocalized, and their energies will be distributed in minibands because of pronounced coupling between the dots (Fig.…”

Theory of relaxation for spontaneous emission of Bloch oscillation radiation2S3 glass

“…Recent progress in nanotechnology makes it possible to fabricate various kinds of SLs that are different from the usual periodically layered QW structures based on III-V compounds. [3][4][5] These examples include quantum-dot SLs of varying dimensionality (1D, 2D, and 3D SLs) [42,43], graphene-based SLs [44][45][46], and natural SLs in SiC crystals [47], which, in particular, have been investigated for the practical realization of a Blochoscillation terahertz generator [48][49][50][51][52].…”

Near-IR photoluminescence from Si/Ge nanowire-grown silicon wafers: effect of HF treatment

“…One of the most important results of the strain and size effects in Si and Ge is the observation of enhanced transition associated with direct band gap material [7] [8]. However, mini-band formation through electronic band structure change from type-II (indirect) to type-I (direct) was proposed to explain the experimental results in strained Si/Ge superlattices [9].…”