Radiative recombination processes in p-type modulation-doped SiGe quantum wells and Si epilayers (original) (raw)
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Semiconductors, 2006
The results of the analysis of variations in the radiative recombination coefficient with varying doping level and concentration of excess electron-hole pairs are reported. It is shown that, along with the effect of narrowing of the band gap calculated in the many-electron approximation, the effect of screening of the Coulomb interaction responsible for the decrease in the exciton binding energy should be taken into account. Both effects produce similar trends and decrease the radiative recombination coefficient with increasing levels of doping or injection. The contributions of excitonic radiative recombination and band-to-band radiative recombination to the total radiative recombination coefficient are separated from each other. It is shown that, in the region of room temperature, both contributions are comparable, while at liquid-nitrogen temperature, the excitonic component dominates over the band-to-band component. The results obtained by refined calculations of the limiting value of the internal quantum yield of electroluminescence for the silicon diodes and p-in structures are presented. It is shown that the internal quantum yield of electroluminescence can be as high as 14%. However, this values sharply decreases with increasing surface recombination rate and decreasing lifetime of excess charge carriers in the bulk.
Electroluminescence and photoluminescence of Si/SiGe self-assembly quantum dot structures
1998
Comparative electroluminescence (EL) and photoluminescence (PL) measurements were performed on Si/Si0.6Ge0.4 self-assembly quantum dots (QDs) structures. The samples were grown pseudomorphically by molecular beam epitaxy, and PIN diodes for electroluminescence were fabricated. Assisted TEM pictures shows the SiGe self-assembly QDs are plate-like. And it showed that the diameters of QDs are in range from 40 nm to 140 nm with the most in 120 nm. Both EL and PL has a wide luminescence peak due to wide distribution of QDs dimensions. At low temperature (T equals 14 K), EL peak has a red shift compared to the corresponding PL peak. Its full-width at half- maximum (FWHM) is about 97 meV, a little smaller than that of corresponding PL peak. The reasons of position and FWHM changes of EL peak from QDs have been discussed.
Intense photoluminescence observed in modulation doped Si/SiGe quantum well structures
Applied Surface Science, 1996
p-type modulation doped wide Si/SiGe quantum well (QW) structures have been grown using a solid-source molecular beam epitaxy system. Very intense SiGe-related photoluminescence (PL) peaks, more than an order of magnitude stronger than for undoped SiGe QW structures, were observed from these samples. The increased PL intensity is believed to be due to the electron confinement in the vicinity of the QW, which enhances its excitonic recombination process in the SiGe layer, and it also indicates high crystalline quality of the grown materials with low incorporation of non-radiative defects. The luminescence properties of these modulation doped SiGe well structures have been studied under various excitation and measurement temperature conditions. Differences in PL spectra from MBE and some CVD grown Si/SiGe samples are discussed.
Photoluminescence excitation spectroscopy of self-assembled SiGe/Si quantum dots
2009
Rapid Communications Rapid Communications are intended for the accelerated publication of important new results and are therefore giuen priority treatment both in the editorial once and in production 3. Rapid Communication in Physical Review B should be no longer than four printed pages and must be accompanied by an abstract Pa. ge proofs are sent to authors
Structural and Luminescence Properties of SiGe Nanostructures with Ge Quantum Dots
Research Journal of Environmental and Earth Sciences, 2014
A study of technological parameters of growing of SiGe like number of Ge nano layers, layers thickness and temperature of substrate are reported. These parameters play an important role in the optical properties of SiGe nanostructures with Ge quantum dots. A long lifetime of radiative recombination for band-to-band transition is attributed to indirect band in Si. As a consequence, the dominant recombination at deep level defects is nonradiative. In order to enhance the intensity of luminescence band at 0.8 eV that related to radiative recombination of Ge quantum dots, the hydrogen plasma ion treatment of SiGe nanostructure were utilized. Improving of the luminescence intensity is an important parameter to increase the quantum efficiency of optoelectronic devices based on the Si nano layer with Ge quantum dots.
Frontiers in Materials, 2016
Fast optical interconnects together with an associated light emitter that are both compatible with conventional Si-based complementary metal-oxide-semiconductor (CMOS) integrated circuit technology is an unavoidable requirement for the next-generation microprocessors and computers. Self-assembled Si/Si1−xGex nanostructures (NSs), which can emit light at wavelengths within the important optical communication wavelength range of 1.3-1.55 μm, are already compatible with standard CMOS practices. However, the expected long carrier radiative lifetimes observed to date in Si and Si/Si1−xGex NSs have prevented the attainment of efficient light-emitting devices, including the desired lasers. Thus, the engineering of Si/ Si1−xGex heterostructures having a controlled composition and sharp interfaces is crucial for producing the requisite fast and efficient photoluminescence (PL) at energies in the range of 0.8-0.9 eV. In this paper, we assess how the nature of the interfaces between SiGe NSs and Si in heterostructures strongly affects carrier mobility and recombination for physical confinement in three dimensions (corresponding to the case of quantum dots), two dimensions (corresponding to quantum wires), and one dimension (corresponding to quantum wells). The interface sharpness is influenced by many factors, such as growth conditions, strain, and thermal processing, which in practice can make it difficult to attain the ideal structures required. This is certainly the case for NS confinement in one dimension. However, we demonstrate that axial Si/Ge nanowire (NW) heterojunctions (HJs) with a Si/ Ge NW diameter in the range 50-120 nm produce a clear PL signal associated with bandto-band electron-hole recombination at the NW HJ that is attributed to a specific interfacial SiGe alloy composition. For three-dimensional confinement, the experiments outlined here show that two quite different Si1−xGex NSs incorporated into a Si0.6Ge0.4 wavy superlattice structure display PL of high intensity while exhibiting a characteristic decay time that is up to 1000 times shorter than that found in conventional Si/SiGe NSs. The non-exponential PL decay found experimentally in Si/SiGe NSs can be interpreted as resulting from variations in the separation distance between electrons and holes at the Si/SiGe heterointerface. The results demonstrate that a sharp Si/SiGe heterointerface acts to reduce the carrier radiative recombination lifetime and increase the PL quantum efficiency, which makes these SiGe NSs favorable candidates for future light-emitting device applications in CMOS technology.
Excitation dependence of photoluminescence in silicon quantum dots
New Journal of Physics, 2007
We have studied the optical properties of silicon quantum dots (QDs) embedded in a silicon oxide matrix using photoluminescence (PL) and time-resolved PL. A broad luminescence band is observed in the red region, in which the time evolution exhibits a stretched exponential decay. With increasing excitation intensity a significant saturation effect is observed. Direct electron-hole recombination is the dominant effect in the red band. A relatively narrow peak appears around 1.5 eV, which is attributed to the interface states overlapping with transition from the ground state of the silicon QDs. The saturation factor increases slowly with detection photon energy between 1.5 and 1.8 eV, which is attributed to the emission from zerophonon electron-hole recombination. At higher photon energies the significantly increased saturation factor suggests a different emission mechanism, most likely the defect states from silicon, silicon oxide or silicon rich oxide.
Light generation and energy transfer in silicon quantum dots
science.uva.nl
While silicon is the primary material used in electronic, microelectronic and photovoltaic technology, it lacks the ability to emit light, because of its indirect bandgap. At the same time, there is a enormous demand for silicon-based light emitters. This thesis describes photoluminescence studies performed on two different systems based on silicon, which are capable of emitting light. The first comprises silicon nanocrystals embedded in a SiO 2 matrix, where quantum confinement effects increase the chance for radiative recombinations of excited carriers. It is shown that there is a limit to the maximum amount of photons generated by the silicon nanocrystals after pulsed excitation, which is determined by their concentration. The second system capable of luminescence is that of silicon nanocrystals and erbium ions dispersed in a SiO 2 matrix. The nanocrystals will in this case transfer their energy to erbium and in that way act as effective sensitizers of the erbium luminescence. It is demonstrated that for both systems the mechanism of luminescence changes with excitation wavelength. When the quantum energy of the incoming photon exceeds a certain threshold value, an additional energy transfer appears, increasing the "quantum efficiency" of photoluminescence . The microscopic details of this mechanism are considered and its potential for photovoltaic applications is commented upon.