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The incorporation behavior of Er into Si and Si 0.88 Ge 0.12 using ErF 3 and Er 2 O 3 as dopant sources during molecular beam epitaxy has been studied. The Er-compounds were thermally evaporated from a high-temperature source. Dissociation of Er 2 O 3 took place and reaction with graphite parts in the high temperature source gave an increased CO background pressure and evaporation of metallic Er. Surface segregation of Er may be strong, but with a high CO or F background pressure, the surface segregation could be reduced and sharp Er concentration profiles were obtained. Transmission electron microscopy analysis shows that it is possible to prepare high crystalline quality structures with Er concentrations up to 4×10 19 cm −3 using Er 2 O 3 and a high F background pressure. Using ErF 3 compound as source material a F/Er incorporation ratio of approximately three has been measured by secondary ion mass spectrometry. Fluorine incorporation can occur not only from evaporated units of ErF 3 molecules, but also from CF x ( x =1–4) and F background species, which are present due to a reaction between the ErF 3 source material and the graphite crucible in the source. After careful degassing of the source, the partial pressures of these species can be significantly reduced. By producing an Er-doped multilayer structure consisting of alternating doped layers grown at low temperature (350°C) and undoped layers grown at a higher temperature (630°C), a flat surface could be maintained during the growth sequence. In this way it was possible to prepare Er-doped structures with an average Er concentration of 1×10 19 cm −3 and without observable defects using ErF 3 as source material. For the case of Er-doping of Si 0.88 Ge 0.12 using ErF 3 , we observed contrast along lines in the growth direction at an Er concentration of 1×10 19 cm −3 , which was attributed to Si concentration variations. Intense emission related to Er has been observed by electro- and photoluminescence.

Various light emitting devices (LED) have been processed using Er/O- and Er/F-doped Si layered structures grown by molecular beam epitaxy (MBE) at low temperature. A comparative study has been carried out in order to provide more understanding of the electroluminescence (EL) excitation and de-excitation mechanisms in particular at a high injection current regime. Comparing the experimental results with model calculations the values of excitation cross section, σ ex , and effective Auger coefficient, C A , have been determined for various devices operated at different biases. Time-resolved EL measurements of these Er/O- and Er/F-doped MBE Si structures, using an experimental set-up with a time response of 200 ns, have been performed with different excitation conditions. Besides the spontaneous Er emission (∼700 μs), some fast EL decay processes associated with the Auger energy transfer via free carriers (∼4 μs), and the hot carrier effects (≲200 ns) have been identified.

Er doped Si layer structures have been grown using Er2O3 or ErF3 as evaporation source materials during Si molecular beam epitaxy. By using a low temperature growth process, an Er doping level of ~5×1019/cm3 has been achieved without precipitation. Structural and luminescence properties of these Er/O and Er/F doped Si samples have been studied. Electroluminescence (1.54 μm) has been observed from Er/O doped Si layers at room temperature through hot electron impact excitation. Comparison of the photo- and electroluminescence of these Er-doped Si structures has been made. The major thermal quenching behaviors of both luminescence emissions are characterized by the same activation energy value of ~160 meV, but different on-set temperatures.

Dopant surface segregation during molecular beam epitaxy (MBE) growth is a serious problem for controlling the doping profiles. To understand the segregation mechanism is essential. In this study, we report the B segregation ratio values, determined using concentration transient analysis based on secondary ion mass spectrometry (SIMS) measurements, for Si and SiGe, respectively. For a comparison, segregation ratio calculations based on a simplified two-site exchange model were performed. It is found that the surface segregation effects of B and Ge during MBE Si growth are interconnected, where the lattice strain likely plays an important role.

This paper reports our recent results on a new method for controlling the internal strain and light emission in Si–Si 1− x Ge x quantum dots (QD) by coating a special SiN x layer with controlled built-in stress. It was found that by changing the stress in the coating layer, a systematic change of photoluminescence intensity and peak position has been observed. An optimum experimental regime was found where improved light emission remains after the SiN x coating. This provides a general way of preparing a stable dielectric film suitable for and controlling the internal strain in the QD diodes and other structures.

Using synchrotron X-ray two-dimensional reciprocal space mapping around the (004) and (224) reciprocal lattice points, we have studied the changes of the lattice strain in a 30-period 3 nm Si/3 nm Si 0.7 Ge 0.3 superlattice (SL) that has been processed into a φ ≈50 nm columnar dot array by e-beam patterning combined with reactive ion etching. It has been found that the superlattice within the columns was partially relaxed after nano-fabrication. The observation of high-order SL satellites from columnar dots indicates a good long-range ordering of SL layers. An analysis based on elastic theory showed that the strain relief in the superlattice occurs by a partial relaxation in SiGe layers together with a biaxial lattice expansion in the thin Si layers, i.e. a strain symmetrisation effect. A staggered band line-up between Si and SiGe is then expected. We propose that an enhanced recombination between electrons and holes confined in adjacent quantum wells at the hetero-interfaces may give rise to the observed increase in the luminescence efficiency in this type of structures.

The fabrication and room temperature light emission of a series of 50 nm Si–SiGe quantum dot diodes emitting light at about 1.3 μm are reported. These diodes are made from molecular beam epitaxially (MBE) grown p – i – n structures with the active region being either a superlattice or a single heterolayer. It was found that the electrical-to-optical power conversion efficiency of the diodes was 0.14%. Possible light emission mechanisms and technological aspects of the work are discussed.

We have calculated the Hall factor in strained p-type ${\mathrm{Si}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$ alloy grown on (001) Si, taking into account the detailed valence-band structure. Acoustic-phonon, nonpolar optical-phonon, alloy, and ionized-impurity scattering are included. It is demonstrated experimentally that the Hall factor can be reduced by a factor of 2 when alloying Si with Ge. Theoretically we have shown that the Hall factor is significantly reduced because of the nonparabolic and nonspherical effects in the valence-band structure. The theory explains experimental results very well. It is also shown that the low-temperature Hall factor is independent of scattering mechanisms. It depends only on the energy band structure. \textcopyright{} 1996 The American Physical Society.

Two-dimensional (2D) reciprocal space mapping of high-resolution X-ray diffraction has been used to characterize the strain in structures with Ge1−xSix and heavily B-doped Ge layers grown by molecular beam epitaxy on Ge (001). Tetragonal lattice distortion yielding strain along and perpendicular to the surface has been determined for Si fractions from 10 to 40% and B concentrations in the range from 6 × 1019 to 8 × 1020cm−3. A sensitive estimate of the critical thickness for Ge1−xSix layers grown on Ge has been obtained by analyzing 2D-reciprocal space maps around the (113) reflection. The lattice contraction coefficient due to B doping in Ge was β = 4.3 × 10−24cm3 per B atom. For CB ≥ 2.2 × 1020cm−3, B precipitation in the form of epitaxial interfacial layers on (001) and (113) planes in the Ge was observed by cross-sectional transmission electron microscopy. Electrical characterization of the samples showed that doping concentrations ≤ 2 × 1020cm−3 could be fully activated.

High-resolution reciprocal lattice mapping (HRRLM) has been used to characterize the strain and thermal stability of undoped, Sb-, and B-doped Si/Si 1-x Ge x (0.16 ≤ x ≤ 0.20) heterostructures grown at temperatures from 300 to 620°C. HRRLM shows no mosaic broadening for Si 1-x Ge x as-grown samples with layer thickness up to 1500 A. Annealing of undoped Si 1-x Ge x layers grown at 300°C or B- or Sb-doped layers grown at 400°C leads to the onset of relaxation already at 500°C. This is in contrast to undoped Si 1-x Ge x layers grown at 600°C which appear to be stable at this annealing temperature. The significantly reduced relaxation temperature in doped layers or layers grown at low temperature is attributed to a decreased activation barrier for nucleation of misfit dislocations in layers with a high concentration of point defects including dopant atoms.

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.

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.

50 nm quantum dots have been fabricated from MBE grown structures with 15 periods of 3 nm-Si-3 nm-Si0.7Ge0.3 superlattices sandwiched between a Si substrate with a 70 nm undoped buffer layer and a 42 nm Si capping layer using electron beam patterning and reactive ion etching. Studies by electroluminescence (EL) and photoluminescence (PL) at temperatures between 4.2 K and room temperature show that both the EL and PL efficiencies were improved by more than two orders of magnitude relative to the as-grown superlattice structures. Efficient EL is observed even at room temperature.

Quantum dots of 50 ~ 60 nm diameter fabricated from both Si/Si1-xGex (x = 0.1 ~ 0.3) strained layer superlattices and a strain symmetried Si9/Ge6 superlattice were investigated by a combination of Raman scattering, photoluminescence, and electroluminescence spectroscopy. It was found that, in addition to an enhanced luminescence intensity of the dots by over two orders of magnitude and improved luminescence quenching temperature, all of the nanostructure dots have residual built-in elastic strains, which are of the order of ~50% of the values in corresponding pseudomorphic heterostructures. This result suggests a possible mechanism for explaining the huge enhancement of the optical efficiency in our luminescence measurements.

Effects of modulation doping on the radiative recombination in Si thin films and SiGe quantum wells (QWs) grown by molecular beam epitaxy are studied in details by photoluminescence (PL) spectroscopy. It is shown that the formation of a two-dimensional hole gas, either in the SiGe QWs or in the doping-induced notch potential in Si thin films, manifests itself in the appearance of characteristic broad luminescence bands. The PL properties are found to be strongly dependent on structure parameters as well as on the experimental conditions, such as photo-excitation intensity and measurement temperature. In the modulation doped SiGe QWs the recombination process is shown to be strongly affected by correlation phenomena, such as Fermi edge singularity.

Cross-sectional transmission electron microscopy (XTEM) has been used to characterize the defect structure of as-grown and annealed highly boron-doped Si, Si 1 − x Ge x ( x ≤ 0.18) and Ge layers grown by molecular beam epitaxy. The structures have also been analyzed with two-dimensional (2D) reciprocal space mapping using high-resolution X-ray diffraction (HRXRD). The boron concentration ( C B ) was in the range from 3 × 10 19 to 8 × 10 20 cm −3 . Si and Si 1 − x Ge x layers were grown at 400°C and Ge layers at 325°C. XTEM micrographs show no crystalline defects in Si and Si 1 − x Ge x samples for C B ≤ 3 × 10 20 cm −3 . However, for C B = 8 × 10 20 cm −3 , B precipitation in the form of epitaxial layer (2D) precipitates on (001) planes in Si and Si 1 − x Ge x and both (001) and (113) planes in Ge was observed. After annealing the B-doped Si and SiGe samples with C B = 8 × 10 20 cm −3 at 1000°C for 15 min, a large number of discrete, 3D, B-related precipitates were observed. For B-doped Ge samples, the thermal stability was poor and B precipitation and severe roughening were observed after annealing at 650°C for 15 min.

Design, performance test, doping capability and grown material quality of a Balzers UMS 630 Si MBE system are reported, particularly concerning measures to obtain good quality of grown films. Good stability, reproducibility and uniformity of deposition rates (Si and Ge) and doping concentrations (Sb and B) have been obtained for growth on a 4 inch Si wafer with sample rotation using a mass-spectrometry controlled e-beam evaporation system, and home-made doping sources, respectively. The quality of grown undoped and modulation doped Si and SiGe layered structures were evaluated using high-resolution XRD, XTEM, SIMS, Hall, and PL measurements. Intense and sharp excitonic PL transitions and high carrier mobility obtained from the grown Si SiGe heterostructures and quantum wells grown at a wide substrate temperature range (320–650°C) indicate high crystalline quality of grown films. Finally, test HBT structures with a thin SiGe base have been made. Good dc characteristics and frequency performance were obtained.

High resolution X-ray diffraction measurements have been done on Si(001)-based structures grown by molecular beam epitaxy (MBE). By systematically varying the angle of incidence and the diffraction angle, the diffraction intensity data can be displayed in a two-dimensional X-ray diffraction intensity map that can be interpretted as a reciprocal space map of the reciprocal lattice points. The experimental technique is described and results for studies of the strain and the strain relaxation with high temperature annealing are described for the following material systems: strained Si/Si1−xGex heterostructures, highly B-doped Si layers on Si and highly B-doped Si1−xGex layers on Si. The strain relaxation in Si1xGex layers occurs via generation of misfit dislocations creating a shift and a characteristic mosaic broadening of the layer peak in the reciprocal space maps. A summary of how the degree of relaxation, as measured from reciprocal space maps, depends on the annealing temperature and the layer thickness is given. The relaxation of the strain induced by B, for doping concentrations up to 5 × 1020 cm−3, is obtained by diffusion of B into the substrate. For a Si0.82Ge0.18 layer with partially compensated compressive strain due to a B concentration of 3 × 1020cm−3, the maps show a combination of strain relaxation via misfit dislocations and B diffusion into the substrate.

Different aspects of boron doping have been studied for silicon and Si 1− x Ge x layers grown by molecular beam epitaxy. Boron segregation at high doping levels was measured in situ in both cases and it was found to be relatively suppressed in the alloy samples. Some possible mechanisms for this effect are discussed. Germanium segregation was also measured during the growth of the first monolayers in Si 1− x Ge x structures. The limits for boron incorporation and activation as dopant in such structures are discussed on the basis of electrical measurements.

Antimony surface segregation during Si(001) molecular beam epitaxy (MBE) was investigated at temperatures Ts = 515−800 °C using concentration transient analysis (CTA). The dopant surface coverage θ, bulk fraction γ, and incorporation probability σ during MBE were determined from secondary-ion mass spectrometry depth profiles of modulation-doped films. Programmed Ts changes during growth were used to trap the surface-segregated dopant overlayer, producing concentration spikes whose integrated area corresponds to θ. Thermal antimony doping by coevaporation was found to result in segregation strongly dependent on Ts with θSb values up to 0.9 monolayers (ML): in films doped with Sb+ ions accelerated by 100 V, θSb was less than or equal to 4 × 10−3 ML. Surface segregation of coevaporated antimony was kinetically limited for the film growth conditions in these experiments.

Les atomes ne sont ni positionnes dans la configuration interstitielle centree par liaison, ni positionnes dans une forme connue de precipites. Le pic d'absorption presente plus de similarites avec la position interstitielle qu'avec la liaison Si-O dans SiO 2 . La largeur elevee de la bande d'absorption reflete probablement des interactions a courte distance des atomes d'oxygene vibrant dans le reseau

The requirements of Si-based photonic devices in the next generation of chip technologies have caused extensive studies on Ge/Si quantum dot devices. In this communication, we report on lateral three-terminal FET type of photodetectors based on Ge dot layers sandwiched between SiGe QWs, where the near-infrared light was mainly absorbed in the Ge island layers. In addition to the source and drain contacts, a gate contact was implemented to control the carrier transfer along the layer stack direction. Very high photo-response was observed with a negative gate bias, accompanied with a significant increase of the carrier lifetime

Thermal quenching of photoluminescence from SiGe/Si quantum wells (QWs) grown by low-temperature molecular beam epitaxy is shown to be significantly improved by postgrowth thermal annealing. The dominant mechanism responsible for this improvement is shown to be a reduction of grown-in nonradiative defects, such as vacancy-related complexes. Postgrowth hydrogenation is demonstrated to be less effective as compared to thermal annealing in removing the nonradiative defects. Selective optical excitation has been used to determine the relative contributions of nonradiative recombination channels present in the SiGe QWs and the Si barriers.

Preparation of pseudomorphic Si1−yCy/Si(001) heterostructures using Si molecular beam epitaxy with C obtained from SiC sublimation in a high-temperature cell has been studied. Thick (≈2000 A) homogenous Si1−yCy layers, y⩽1.5%, and Si1−yCy/Si multiple quantum well (MQW) structures, y⩽8%, have been prepared. There is a growth temperature dependent surface roughness accumulating during the growth sequence that can lead to reduction of C induced strain. Temperature modulation during growth has been used to suppress this effect. Near band gap photoluminescence is reported from Si1−yCy/Si MQW structures.

Er, together with oxygen or fluorine as co-dopants, has been incorporated into Si during molecular beam epitaxial growth using co-evaporation of Si and Er containing compounds. The Er doping concentration using both Er2O3 and ErF3 can reach a level of ∼5×1019 cm−3 without precipitation, which is at least one order of magnitude higher than a previously reported solid solubility limit for Er in Si. Growth, structural, and luminescence characterization of these Er/O and Er/F doped Si samples are reported. In particular, 1.54 μm electroluminescence has been observed from Er/O doped Si layers at room temperature through hot electron impact excitation.

Influence of postgrowth hydrogen treatments on nonradiative recombination centers in undoped and B-doped Si epilayers, grown by molecular beam epitaxy at low temperatures, are studied by optical detection of magnetic resonance. Hydrogen passivation of the dominant nonradiative defects in undoped Si is shown to be rather effective, whereas in the B-doped Si epilayers the effects of the hydrogen treatment of the same defects are found to be only marginal. Possible mechanisms for this are discussed. Information on two new nonradiative defects is provided.

This paper demonstrates the fabrication of near infrared MESFET photodetectors. This study shows that photon absorption occurs in Ge quantum dots while the lateral transport of photo-carriers is facilitated by high mobility 2D SiGe quantum wells next to the dot layers. High photo-response at normal incidence are measured, with the highest responsivity of 140 mA/W (1.31 /spl mu/m) and >35 mA/W (1.55 /spl mu/m) at room temperature. The measured integrated photo-responsivity for the photon beam with energies below the Si bandgap is >200 mA/W at V/sub DS/ = -2.5 V and V/sub G/ = 2 V. The time-resolved photoconductivity measurements and switch properties of these MESFET photodetectors are also studied with switching frequency of 3 MHz, which is the upper limit of the instrument bandwidth.

We have investigated the luminescence properties of the spatially indirect transition in Stranski‐Krastanov grown Si/Ge quantum dots. Two different diodes were grown and studied in terms of energy position, temperature, and electric field dependence. Our results show that the notch potential for electrons at the interface above the Ge quantum dot is deeper than the one underneath, and we attribute this to an asymmetric strain profile as a result of the quantum dot layer geometry. Furthermore, we present the first study of the quantum‐confined Stark effect for Si/Ge quantum dots produced by Stranski‐Krastanov growth. We observe a linear blue shift of the transition energy with increasing electric field, an observation in sharp contrast to what is generally accepted for type‐I systems, where the quantum‐confined Stark effect causes a quadratic red shift of the transition energy.

Important grown‐in nonradiative defects in Si epilayers and SiGe/Si heterostructures prepared by molecular beam epitaxy are studied by the optically detected magnetic resonance technique. Several nonradiative defects are observed that have been introduced by ion bombardment during growth or by the low surface adatom mobility during low‐temperature growth. These defects are shown to provide efficient nonradiative channels for carrier recombination and, to a large extent, control the carrier lifetime.

Growth of Si and SiGe layers using molecular beam epitaxy was carried out with the substrate at a floating, positive or negative bias, in order to investigate effects of ion bombardment on the crystalline quality of grown materials. Although ion energies (100–1500 eV) and ion/atom flux ratios (∼0.005) used in the experiments were quite low, significant lattice distortion along the growth direction (Δa⊥/as up to ∼300 ppm) was observed by high resolution x‐ray diffraction from the Si layers grown at 420 °C. At the same time, a broadband transition was observed in photoluminescence measurements from both Si and SiGe layers. Based on results of the annihilation behavior during postgrowth treatments using thermal annealing and hydrogenation, we attribute these effects to the ion bombardment induced formation and injection of different types of pointlike defects and defect clusters, which degrade the optical and electrical properties of grown layers.

The appearance of broad photoluminescence (PL) bands in the energy range 0.70–0.96 eV in SiGe/Si heterostructures is shown to be related to the ion bombardment during the molecular beam epitaxy. From the optically detected cyclotron resonance, polarization, and postgrowth treatments, the PL is shown to be composed of at least two components. No evidence of lattice distortion is found for the main PL band, while the low energy tail is believed to arise from lattice distorted regions. Both PL centers are demonstrated to originate from the SiGe quantum wells by PL excitation measurements.

Recent research interests on the development of Si-based light emitting devices have been highly motivated by the demands of optical interconnects in the Si CMOS chip technology, in view of monolithic integration of optoelectronic devices on a Si chip to produce a new generation of high density high performance CMOS ICs with high reliability and low cost. As predicted in the SIA roadmap, accompanying with the fast reduction the device feature size, the maximum interconnect length will also increase from the present ∼2 km on a logic chip to ≥20 km in 10 years. The circuit performance of CMOS will then be limited by the bandwidth of conventional electronic interconnects. It is desirable to develop fully Si-based optical interconnects. However, a highly efficient Si light emitter is so far missing, due to the inherent indirect bandgap of Si. Many different approaches have been proposed and a lot of effort has been made during the past few years. Er-doping in Si has attracted some special interest [1] due to observations of intense and sharp electroluminescence (EL) at the interesting wavelength of 1.54 μm at room temperature from structures containing layers that are doped with Er to concentrations of 0.1-2x1020 cm-3 made by either low-temperature ion implantation followed by a solid phase epitaxy process, [2] or molecular beam epitaxy (MBE). [4]. Er-doped light emitting devices have several advantages in optical interconnect applications. The transition, which emits the light, is between atomic levels, so that the same output wavelength can be obtained from device to device and from wafer to wafer. Furthermore, it does not depend on the heat-sink temperature, which is a usual problem with light emission via band-to-band recombination in semiconductor homo- or hetero-structures. There are several other important issues regarding output power and modulation frequency of Er-doped light emitting sources, in particular, how the Er-ions are optically activated and being effectively pumped to obtain an optical gain. Since a long spontaneous decay time of Er emission limits Er- doped LEDs to be used as a power efficient device at high modulation frequency, to achieve stimulated emission is thus a key to making Er-doped Si materials and devices feasible for the use of optical interconnects.

High quality, strained Si/Si1−xGex layered structures have been grown at temperatures in the range 400–625 °C, using a solid‐source molecular‐beam epitaxy (MBE) system with a mass‐spectrometry‐based loop‐control to improve the accuracy and stability of the evaporation rates. Good control of the growth parameters has been achieved as verified by, e.g., high‐resolution x‐ray diffraction. Very high intensities and extremely small peak widths, down to 2.7 meV for the XNP transition at low excitation levels of photoluminescence spectra, indicate high crystalline quality of the layers. It is shown that some previously reported defect‐related luminescence from MBE‐grown SiGe layers is not intrinsic to the MBE process.

Large enhancements in the electron mobility are reported for structures containing a pair of closely spaced Sb δ‐doped layers in Si. The room‐temperature mobility is enhanced by a factor of 2 compared to corresponding uniformly doped layers of singly δ‐doped structures. Even higher mobilities were obtained by using a Schottky gate on top and applying a voltage to adjust the potential well. With an effective gate voltage of ∼−0.3 V the mobility was 1200 cm2 V−1 s−1 at room temperature, which is an enhancement by a factor of 10 relative to the layer with equivalent bulk doping concentration. The high mobility is attributed to wave functions with nodes at the δ‐doped layers.

The low temperature current gain and the low frequency noise are important parameters of the preamplifiers of the integrated IR receiver system. Si/Si1-xGex heterojunction bipolar transistors (HBTs) have potential advantages used in the preamplifiers at low temperature. In this paper, we analyze the characteristics of the current gain and low frequency noise of Si/Si1-xGexHBTs at low temperature. They are influenced by the following factors: (1) the energy band offset of the emitter-base junction; (2) the high doping effect, the low temperature freeze out effect in the emitter region and base region; (3) the influence of germanium (Ge) content and profile in the base region on the transport performance; (4) the Si/Si1-xGex interface recombination currents and surface recombination currents; (5) the collector-base heterojunction barrier effect. Then we give the physical analysis model and noise analysis model of Si/Si1-xGexHBTs at low temperature. Based on this, we present the equivalent circuit and equivalent noise circuit at low temperature and simulate and optimize the characteristics of the current gain and the noise of Si/Si1-xGex HBT for IR integrated receiver system. The current gain (beta) max equals 300, and the low temperature current gain (beta) max equals 8100 at 77K, at high injection level. We optimize the design of Si/SiGe HBT-based monolithically integrated preamplifier applied to IR receiver system at low temperature.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In this work we study effects of growth temperature and use of surfactant during growth on thermal quenching of photoluminescence (PL) from SiGe/Si quantum wells (QWs) grown by molecular beam epitaxy (MBE). We show that although all investigated structures demonstrate intense and sharp excitonic emissions from the SiGe QWs at liquid helium temperature, thermal quenching of this PL critically depends on the growth conditions. In particular, the use of low (⁤ 550°C) growth temperatures or employing Sb as a surfactant during high temperature (620°C) growth considerably degrades the PL thermal quenching behaviour by introducing some competing quenching processes with low activation energies of about 5 meV. The optimum growth conditions judging from the PL thermal behaviour are realised during high temperature growth without surfactant (620°C). Even higher growth temperature is shown to be required during surfactant mediated growth to improve the thermal quenching behaviour. From optically detected magnetic resonance (ODMR) studies, the competing quenching processes are attributed to a thermal activation of non-radiative defects introduced during either low-temperature MBE growth or during surfactant-mediated growth.

Arrays of 40 - 50 nm quantum dots were fabricated from Si- Si 1-x Ge x single quantum well and superlattice structures grown by molecular beam epitaxy. The dots showing strong luminescence were studied by synchrotron source x-ray diffraction. Some of the dots were coated with SiN x films containing different build-in stresses. It was found that the luminescence intensity depends strongly on the amount of stress in the SiN x coating, being strongest when the stress was close to zero. A strain symmetrization process occurred in the bright dots. Although an exact physical origin is not yet available, it is exciting that these quantum dot diodes work at room temperature and that the whole fabrication procedure is compatible with Si- technology.

A strong effect of $p$-type modulation doping on the radiative recombination in $\mathrm{Si}/{\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}/\mathrm{Si}$ quantum wells is observed by photoluminescence (PL) spectroscopy. The filling of the Si-Ge quantum wells due to the charge transfer of holes from the $B$ modulation doping in the adjacent Si layers causes an appearance of a broad asymmetric PL band with a characteristic sharp high-energy cutoff. A strong enhancement near the Fermi edge is shown, by varying structure parameters and experimental conditions, to correspond to the Fermi-edge singularity. Experimental evidence on the dominant mechanism responsible for the Fermi-edge singularity is given as due to a nearly resonant scattering between the electronic states near the Fermi energy and the next unoccupied subband of the two-dimensional hole gas.

The radiative recombination processes of the two-dimensional hole gas formed in SiGe quantum wells (QWs) due to modulation doping are studied in details by photoluminescence (PL) spectroscopy. Boron-modulation-doped Si/Sil−xGex/Si heterostructures grown by molecular beam epitaxy (MBE) are studied. It is shown that charge transfer of holes from the doped Si layers causes the filling of the SiGe QWs leading to an appearance of a broad asymmetric PL band with a characteristic sharp high energy cut-off and enhanced recombination near the Fermi edge. A reduction of this PL enhancement is observed with an increase of measuring temperature. The PL bandwidth and the high energy cut-off are found to vary with either the doping level or the spatial separation between the delta-doped layers and the QWs. This PL band is argued to arise from the recombination of the holes in the QWs and electrons confined near the QWs as a result of the band bending induced by the delta-doping. The shape of the PL band with enhanced intensity near the Fermi edge are discussed in terms of the phase space filling and many-body effects.