Room temperature lateral p+-i-n+ light-emitting diodes (LEDs) with photonic crystals embedded in the i-region were fabricated on structures with Ge(Si) self-assembled islands and their optical properties were investigated. The use of preliminary amorphization and solid phase epitaxy of the implanted p+ and n+ contact regions made it possible to reduce the impurity activation temperature from 800 degrees C-1100 degrees C to 600 degrees C, which corresponds to the growth temperature of Ge(Si) islands. This resulted in a significant reduction of the detrimental effect of the high-temperature annealing used for diode formation on the intensity and spectral position of the luminescence signal from the islands. It was shown that significant enhancement (more than an order of magnitude) of room temperature electroluminescence of Ge(Si) islands in the spectral range of 1.3-1.55 mu m can be achieved due to their interaction with different modes of the photonic crystals. The measured radiation power of the obtained diodes in the spectral range of 1.3-1.55 mu m exceeds 50 pW at a pump current of 8 mA, which is an order of magnitude higher than the previously achieved values for micro-LEDs with Ge(Si) nanoislands. The obtained results open up new possibilities for the realization of silicon-based light emitting devices operating at telecommunication wavelengths.

Light-emitting transistors (LETs) represent the next step in the development of light-emitting diodes (LEDs), offering additional control over emission. In this work, the transport properties and spatial distribution of electroluminescence (EL) in the spectral range of 1.2-1.7 mu m were studied for lateral p(+)-i-n(+) LEDs based on silicon-on-insulator structures with self-assembled Ge(Si) islands embedded in photonic crystals. It is shown that due to the low mobility of holes and their effective trapping in the islands, the maximum EL yield is observed at the i/p(+) junction of the LED. It is demonstrated that the sign and magnitude of the bias voltage applied to the substrate (to the gate) have a significant influence on the transport and emission properties of the LEDs with Ge(Si) islands, turning them into LETs. In particular, applying a negative gate voltage shifts the position of the maximum emission region from the i/p(+) to the i/n(+ )junction of the LET, which is related to the formation of a hole conductivity channel near the buried oxide layer. The embedding of a specially designed photonic crystal in the i-region of the LET makes it possible to manage the spectral properties of the near-IR emission by changing the sign of the gate voltage. The results obtained may be useful for the future development of optoelectronic devices.

Due to their widely tunable bandgap, HgCdTe heterostructures with quantum wells are a promising material system for semiconductor lasers in the entire mid-infrared range. Recently, Auger-suppressed structures allowed interband stimulated emission (SE) in the atmospheric transparency window 3–5 μm well above 200 K, while previously it was limited to temperatures below 175 K. In contrast to earlier works focused on ridge or vertical emitting HgCdTe lasers, here we demonstrate a whispering gallery mode microdisk (d = 50 μm) laser operating under optical pumping at ∼4 μm in the temperature range attainable by the thermoelectric cooling. Above 200 K, the emission spectrum consists of multiple 0.37-meV-wide peaks associated with the modes of the disk resonator. Laser generation is achieved up to 230 K, which is 40 K lower than the quenching temperature of SE in the unprocessed macroscopic sample. We associate the difference with the optical losses introduced by the inclined walls of the disk.

The first results on the study of photoluminescence and lasers radiation spectra of a CdHgTe solid solution-based quantum well structure with microdisk cavities of different diameters are demonstrated. It is shown that the presence of cavities contributes to an increase in the maximum operating temperature of generation compared to the unprocessed structure.

Photoluminescence and laser emission spectra of CdHgTe solid-solution quantum-well structures with microdisk cavities of different diameters are demonstrated. The presence of a cavity is shown to contribute to an increase in the maximum operating temperature of generation as compared to the unprocessed structure.

The results of the experimental study and theoretical simulation of the photoluminescence (PL) spectra of strained germanium microbridges with improved heat sink are reported. It was shown that in the structures under study the main contribution to the PL signal of micro-bridges is provided by the radiative transitions from Г-valley to the valence band in the whole considered temperature range (from 80 to 300 K). The influence of interference and self-absorption effects on the shape of the PL spectra of Ge microbridges is discussed. It was demonstrated that Ge microbridges with improved heat sink which was achieved due to the adhesion of the bridges to the underlying layers due to capillary forces are not subjected to the additional stretching as the temperature decreases in contrast to the suspended ones.

The formation of locally strained Ge microstructures (microbridges) on silicon-on-insulator (SOI) substrates embedded into cavities and the results of studies of the optical properties of such structures are reported. A cavity design compatible with the geometry of the locally strained active region is calculated so that it provides, on the one hand, efficient localization of the electromagnetic field in the active region of the structure and, on the other hand, minimizes the influence of the cavity on the magnitude and distribution of strains in the structure. The experimentally obtained microphotoluminescence spectra demonstrate a considerable increase of the signal intensity from the strained regions of Ge microstructures compared to the initial Ge film. It is shown that the formation of cavities yields a reduction of strains in Ge microbridges, but provides an increase of the photoluminescence intensity of the structures.

The results of the experimental study and theoretical simulation of the photoluminescence (PL) spectra of strained germanium microbridges with improved heat sink are reported. It was shown that in the structures under study the main contribution to the PL signal of micro-bridges is provided by the radiative transitions from -valley to the valence band in the whole considered temperature range (from 80 to 300 K). The influence of interference and self-absorption effects on the shape of the PL spectra of Ge microbridges is discussed. It was demonstrated that Ge microbridges with improved heat sink which was achieved due to the adhesion of the bridges to the underlying layers due to capillary forces are not subjected to the additional stretching as the temperature decreases in contrast to the suspended ones. Keywords: SiGe structures, tensile strained Ge, photoluminescence, simulation of the photoluminescence spectra.

In this work, formation of locally tensile strained Ge structures (micro-bridges) on SOI substrates embedded into microcavities is reported and their optical properties are discussed. The cavity compatible with the shape of the active region was designed in such a way as to provide an effective localization of the electromagnetic field in the active region of the structure, as well as to minimize the strain redistribution due to the cavity formation. Micro-photoluminescence (PL) studies have shown a remarkable enhancement of the PL intensity for the locally strained areas as compared to the initial Ge film. It was shown that the formation of a microcavity leads to a decrease in the maximum strain in the active region of the structure, but provides an overall increase in the PL intensity.

In this work formation of locally strained Ge structures on SOI substrates is reported and their optical properties are discussed. Suspended Ge structures were fabricated by optical lithography, plasmachemical and wet chemical etching using the “stress concentration” approach. The fabrication procedure of suspended structures were modified in such a way to provide the mechanical contact between them and the underlying layers so improving the heat dissipation from them. SOI substrates with top Si layer being only 100 nm thick were utilized in such fabrication scheme. The decrease of local heating in such kind of structures was confirmed by the study of micro-Raman scattering depending of scanning laser power. Micro-photoluminescence measurements have shown the remarkable enhancement of the integrated intensity from locally strained areas of a microstructure. It was also shown that structures brought in contact with underlying layers could sustain much higher pumping power densities without fracture as compared to the suspended ones.

The influence of rapid thermal annealing on the electrical and radiative properties of Ge:Sb/Si(001) epitaxial layers with an antimony concentration substantially higher than its equilibrium solubility in germanium is investigated. Local variations in the electrical and luminescence properties of n-Ge/Si(001) throughout the structure depth are investigated by means of the precise chemical etching of Ge. It is shown that a variation in the properties of such layers at relatively low (≤500°C) annealing temperatures (decrease in the electron concentration and photoluminescence intensity) occur in the absence of the noticeable diffusion-related redistribution of dopant atoms. Variations in the electrical and luminescence properties of Ge:Sb layers at relatively high (≥700°C) annealing temperatures are caused by the substantial redistribution of Sb due to its bulk diffusion and desorption from the surface. In particular, Sb diffusion leads to the formation of doped layers in initially undoped parts of the studied structures, which start to give a substantial contribution to the resulting conductivity of the structure and its photoluminescence signal.

The results on the formation of locally strained Ge microstructures on silicon-on-insulator (SOI) substrates and investigation of their optical properties are presented. Suspended Ge structures are formed by optical lithography and plasmachemical and selective chemical etching using the “stress concentration” approach. To provide a heat sink from Ge microstructures, their formation scheme is modified so as to provide the mechanical contact of a part of the suspended microstructure with lower-lying layers. To implement this scheme, SOI substrates with a thin upper Si layer 100 nm in thickness are used. It is shown using the measurements of Raman spectra depending on the pumping power that local heating in such structures decreases. Measurements of the microphotoluminescence spectra show a considerable increase in the signal intensity from strained regions of Ge microstructures as well as the possibility of increasing the maximal optical pumping power (not leading to irreversible changes) for microstructures, in which the mechanical contact of the strained part with lower-lying layers is provided, when compared with suspended structures.

The impact of rapid thermal treatment on electrical and luminescent properties of Ge:Sb/Si(001) layers which have Sb concentration much higher than the equilibrium solubility limit was investigated. Local modifications of such properties throughout the structure’s depth were revealed using precise wet chemical etching. It was obtained that at relatively low annealing temperatures ( 500°С) the changes of electron concentration and photoluminescence response may occur without any remarkable diffusion-related redistribution of dopant atoms. For the relatively high ( 700°С) annealing temperatures the changes of electrical and optical properties after anneal are caused by the significant Sb bulk diffusion and desorption from the sample surface. In particular Sb bulk diffusion leads to the formation of doped regions in the initially undoped areas which further contribute to the resulting structure conductivity and its photoluminescence signal.

AbstractThe formation and properties of locally tensile strained Ge microstructures (“microbridges”) based on Ge layers grown on silicon substrates are investigated. The elastic-strain distribution in suspended Ge microbridges is analyzed theoretically. This analysis indicates that, in order to attain the maximum tensile strain within a microbridge, the accumulation of strain in all corners of the fabricated microstructure has to be minimized. Measurements of the local strain using Raman scattering show significant enhancement of the tensile strain from 0.2–0.25% in the initial Ge film to ~2.4% in the Ge microbridges. A considerable increase in the luminescence intensity and significant modification of its spectrum in the regions of maximum tensile strain in Ge microbridges and in their vicinity as compared to weakly strained regions of the initial Ge film is demonstrated by microphotoluminescence spectroscopy.

In this paper, we report on the formation of heavily n-doped Ge:Sb layers on Si(001) substrates by MBE with active dopant concentration exceeding 1020 cm−3 and discuss their thermal stability. Rapid thermal annealing was applied to the samples with different doping densities being both below and above the equilibrium solubility limit of Sb in Ge. Experimentally obtained changes of the impurity atomic concentration and carrier density were attributed to Sb bulk diffusion, desorption and dopant clustering. The qualitatively different modifications of room-temperature photoluminescence (PL) due to annealing were obtained for the n-Ge layers with different doping levels. In particular, for the doping levels which were below or close to the equilibrium solid solubility the overall positive impact of annealing on the PL intensity was observed. However, for the n-Ge layers with higher doping levels a more complex behavior was obtained, namely, a significant drop followed by the subsequent partial restoration of the PL intensity with the increase of annealing temperature. Changes of the PL response were attributed to the two main processes which occur during thermal treatment—annealing of the point defects generated due to low-temperature growth of a doped layer and dopant cluster formation—which have the opposite impact on the PL intensity. The obtained results allowed us to formulate the recommendations on thermal treatment of the n-type doped Ge layers, which may be useful for Ge-based Si photonics applications.

Simple technique of formation of “black silicon” using wet chemical etching of crystalline Si wafers with SiGe self-assembled islands is proposed. The main idea consists of the utilization of SiGe islands as a mask for wet anisotropic etching of Si in alkali-based solution at the first etching stage and further removal of SiGe residuals by etching in a HF:H2O2:CH3COOH mixture at the second etching stage. Initial samples were the crystalline Si wafers with SiGe islands formed on them by deposition of 2.5–14nm of Ge at 800°C. After the two above-mentioned etching steps a submicron relief on a Si surface was formed. Investigation of optical properties of fabricated structures revealed significant decrease of reflection (AM 1.5G weighted reflection ~2–3%) and increase of absorption in the wavelength range of 500–1200nm. Due to the very small amount of Si removal (<0.5µm), utilization of standard chemicals for Si-based solar cell technology and potential suitability for usage in large-scale manufacturing the proposed technique is promising for increasing of efficiency of thin wafers crystalline Si solar cell.

The formation and properties of locally tensile strained Ge microstructures (“microbridges”) based on Ge layers grown on silicon substrates are investigated. The elastic-strain distribution in suspended Ge microbridges is analyzed theoretically. This analysis indicates that, in order to attain the maximum tensile strain within a microbridge, the accumulation of strain in all corners of the fabricated microstructure has to be minimized. Measurements of the local strain using Raman scattering show significant enhancement of the tensile strain from 0.2–0.25% in the initial Ge film to ~2.4% in the Ge microbridges. A considerable increase in the luminescence intensity and significant modification of its spectrum in the regions of maximum tensile strain in Ge microbridges and in their vicinity as compared to weakly strained regions of the initial Ge film is demonstrated by microphotoluminescence spectroscopy.

В работе для растворов КОН и HF:H2O2:CH3COOH исследована селективность травления SiGe-структур в зависимости от их состава. Полученные результаты предложено использовать для создания на кремнии субмикронного рельефа поверхности за счет селективного травления структур с самоформирующимися наноостровками Ge(Si). В предлагаемом подходе наноостровки Ge(Si) служат маской для селективного травления Si в водном растворе KOH с добавлением изопропилового спирта, а затем удаляются с поверхности селективным травлением в HF:H2O2:CH3COOH. Экспериментально показано, что подобный подход позволяет создавать на кремнии субмикронный рельеф поверхности, который приводит к существенному уменьшению коэффициента отражения в широком спектральном диапазоне. Полагается, что предлагаемый метод создания рельефа поверхности может быть использован для повышения эффективности тонкопленочных солнечных элементов на основе кристаллического кремния. DOI: 10.21883/FTP.2017.12.45170.33