Si/SiGe Heterointerfaces in One-, Two-, and Three-Dimensional Nanostructures: Their Impact on SiGe Light Emission (original) (raw)

Silicon-Germanium Nanostructures for Light Emitters and On-Chip Optical Interconnects

Proceedings of the IEEE, 2000

| In this paper, we review the present status of light emitters based on SiGe nanostructures. In order to be commercially valuable, these light emitters should be efficient, fast, operational at room temperature, and, perhaps most important, compatible with the Bmainstream[ complementary metal-oxide-semiconductor (CMOS) technology. Another important requirement is in the emission wavelength, which should match the optical waveguide low-loss spectral region, i.e., 1.3-1.6 m. Among other approaches, epitaxially grown Si/SiGe quantum wells and quantum dot/quantum well complexes produce efficient photoluminescence and electroluminescence in the required spectral range. Until recently, the major roadblocks for practical applications of these devices were strong thermal quenching of the luminescence quantum efficiency and a long carrier radiative lifetime. The latest progress in the understanding of physics of carrier recombination in Si/SiGe nanostructures is reviewed, and a new route toward CMOS compatible light emitters for on-chip optical interconnects is proposed.

Bright photoluminescence from ordered arrays of SiGe nanowires grown on Si(111)

We report on the optical properties of SiGe nanowires (NWs) grown by molecular beam epitaxy (MBE) in ordered arrays on SiO2/Si(111) substrates. The production method employs Au catalysts with self-limited sizes deposited in SiO2-free sites opened-up in the substrate by focused ion beam patterning for the preferential nucleation and growth of these well-organized NWs. The NWs thus produced have a diameter of 200 nm, a length of 200 nm, and a Ge concentration x = 0.15. Their photoluminescence (PL) spectra were measured at low temperatures (from 6 to 25 K) with excitation at 405 and 458 nm. There are four major features in the energy range of interest (980–1120 meV) at energies of 1040.7, 1082.8, 1092.5, and 1098.5 meV, which are assigned to the NW-transverse optic (TO) Si–Si mode, NW-transverse acoustic (TA), Si–substrate–TO and NW-no-phonon (NP) lines, respectively. From these results the NW TA and TO phonon energies are found to be 15.7 and 57.8 meV, respectively, which agree very well with the values expected for bulk Si1−xGex with x = 0.15, while the measured NW NP energy of 1099 meV would indicate a bulk-like Ge concentration of x = 0.14. Both of these concentrations values, as determined from PL, are in agreement with the target value. The NWs are too large in diameter for a quantum confinement induced energy shift in the band gap. Nevertheless, NW PL is readily observed, indicating that efficient carrier recombination is occurring within the NWs.

Important defect aspects in optoelectronic applications of Si- and SiGe/Si-heterostructures

Applied Surface Science, 1996

We have carried out a systematic investigation of non-radiative defects in Si-epilayers and SiGe/Si-heterostructures grown by molecular beam epitaxy (MBE). A number of non-radiative defects are observed, by the optically detected magnetic resonance (ODMR) technique, and are shown to depend critically on the sample structures and growth conditions. Experimental evidence on the mechanisms for the introduction of these defects are provided. These defects provide efficient non-radiative channels for carrier recombination and, to a large extent, control the carrier lifetime.

Ab initio optoelectronic properties of SiGe nanowires: Role of many-body effects

Physical Review B, 2010

The self-energy and electron-hole interaction corrections to the one-particle approximation for SiGe nanowires have been calculated for different geometries and diameters. We show that, at fixed nanowire diameter and orientation, the self-energy corrections for the SiGe nanowires can be obtained as a weighted average, on the relative composition of one type of atom with respect to the total numbers of atoms in the unit cell, of the corrections for the pure ͑Si and Ge͒ nanowires, thus circumventing cumbersome computations and allowing a direct and practical determination of the electronic band gap. Moreover we show that particular geometrical configurations are at the origin of an enhancement of the optical oscillator strength that should be important for optoelectronic applications.

Fast Luminescence in Silicon-Germanium Nanostructures

ECS Transactions, 2013

Epitaxially-grown three-dimensional Si/SiGe nanostructures produce photoluminescence and electroluminescence in the desired spectral range of 1.3-1.6 μm. We show that by controlling and modifying such Ge-rich SiGe nanoclusters during growth it is possible to fabricate very fast and hence more efficient SiGe lightemitting devices. The physics of carrier recombination in these Si/SiGe nanostructures is discussed. The present results provide another possible route toward CMOS compatible light emitters.

Radiative recombination processes in p-type modulation-doped SiGe quantum wells and Si epilayers

Journal of Crystal Growth, 1995

In this work, it is shown how different carrier recombination paths significantly broaden the photoluminescence (PL) emission bandwidth observed in type-II self-assembled SiGe/Si(001) quantum dots (QDs). QDs grown by molecular beam epitaxy with very homogeneous size distribution, onion-shaped composition profile, and Si capping layer thicknesses varying from 0 to 1100 nm are utilized to assess the optical carrier-recombination paths. By using high-energy photons for PL excitation, electron-hole pairs can be selectively generated either above or below the QD layer and, thus, clearly access two radiative carrier recombination channels. Fitting the charge carrier capture-, loss-and recombination-dynamics to PL time-decay curves measured for different experimental configurations allows to obtain quantitative information of carrier capture-, excitonic-emission-, and Auger-recombination rates in this type-II nano-system.

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.

Doping of SiGe core-shell nanowires

Journal of Computational Electronics, 2012

Dopant deactivation in pure Si and pure Ge nanowires (NWs) can compromise the efficiency of the doping process at nanoscale. Quantum confinement, surface segregation and dielectric mismatch, in different ways, strongly reduce the carrier generation induced by intentional addition of dopants. This issue seems to be critical for the fabrication of high-quality electrical devices for various future applications, such as photovoltaics and nanoelectronics. By means of Density Functional Theory simulations, we show how this limit can be rode out in core-shell silicongermanium NWs (SiGe NWs), playing on the particular energy band alignment that comes out at the Si/Ge interface. We demonstrate how, by choosing the appropriate doping configurations, it is possible to obtain a 1-D electron or hole gas, which has not to be thermally activated and which can furnish carriers also at very low temperatures. Our findings suggest core-shell NWs as possible building blocks for highspeed electronic device and new generation solar cells.