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Band-gap energy of Si 10x Ge x as a function of Ge concentration at room temperature, as determined from photocurrent spectroscopy. The EL results, extrapolated at 300 K using (4), are also shown.
Source publication
We present the photocurrent spectroscopy of
Si<sub>1-x</sub>Ge<sub>x</sub>/Si double heterostructure p-i-n diodes
selectively grown by low pressure chemical vapor deposition. The growth
onto patterned wafers permits to obtain dislocation-free, fully strained
Si<sub>1-x</sub>Ge<sub>x</sub> layers, much above the critical
thickness. The band gap ener...
Contexts in source publication
Context 1
... results obtained for the band-gap energies for the three different samples indicate, as expected, a decrease of effective band-gap energy with increasing Ge content. The following empirical linear expression (see Fig. 5) for the energy band- gap at 300 K of the SiGe strained alloy has been ...
Context 2
... with temperature is similar to that for Si or Ge (4) The coefficients for Si Ge could be determined using a linear interpolation using the values for Si and Ge (Vegard's law). We obtain finally a very good agreement with values reported on Table II (the values for obtained from EL measurements extrapolated at room temperature are depicted in Fig. ...
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Citations
... The photocurrent spectrum measured at room temperature can used to determine the absorption edge (bandgap energy) of the detector utilizing the curve-fitting technique. Using the tangent lines in the (I ph •hν) 2 and energy diagrams for direct band material [41,42], we obtain the bandgap of 3.63 eV, as shown in figure 8(c), which is self-correcting with the value in figure 4(c). Figure 8(d) shows the real-time response of the Metal-MoO x -Metal structural detector under periodic illumination with xenon light, and the obvious photoresponse period can be observed from the response time spectrum. ...
We propose a simple approach to locally modify the conductance of molybdenum oxide thin films with thermal annealing in oxygen atmosphere at relatively low temperature for constructing a visible- blind ultraviolet photoconductor. The amorphous MoO x is grown by remote plasma enhanced atomic layer deposition (RPALD), and then crystallized into α-MoO x at 500 ℃ in argon atmosphere, which exhibits good conductance with resistivity of 3.9x10 ⁻³ Ω•cm due to the formation of oxygen vacancies. Good ohmic contact between Ti and the crystallized MoO x is demonstrated with specific contact resistance of 9.74x10 ⁻⁴ Ω•cm ² . The lateral Au/Ti- MoO x - Ti/Au structures are defined and the conductance of the exposed MoO x channel is significantly modified by thermal annealing in oxygen atmosphere to form a photodetector, which shows obvious photoresponse at the wavelength of less than 372 nm with low dark current of 0.9 pA at 5 V, and the remarkable responsivity of 0.75 mA/W at 280 nm is achieved with a high ultravoilet/visible rejection ratio. The low dark current and incredible responsivity can be attributed to the good ohmic contacts of untreated MoO x and the reduction of number of oxygen vacancies in the MoO x channel. The key role of oxygen vacancy on the conductance of MoO x has been demonstrated. Those results suggest that the MoO x thin films are promising candidate for visible- blind ultraviolet photodetectors in a simple CMOS- compatible process.
... As Ge concentration x increases, the band gap of Si 1−x Ge x narrows, and the absorption coefficient of the SH wave increases [27,28]. Thus, the attenuation of the incoming fundamental and outgoing SH waves in the Si/SiGe structure can be estimated as a continuous material with absorption coefficients ...
Si/SiGe stacked multilayers are key elements in fabrication of gate-all-around (GAA) structures and improvement of electrical properties, with the evolution of the Si/SiGe interfaces playing a crucial role. In this work, a model is developed based on the simplified bond hyperpolarizability model (SBHM) to analysis the anisotropic reflective second harmonic generation (Ani-RSHG) on a three-period stacked Si/Si1−xGex multilayer, which builds on Si(100) diamond structures. The C4v symmetry of the Si(100) structure enables the second harmonic generation (SHG) contribution from the bonds to be simplified and the effective hyperpolarizabilities of the interfacial and bulk sources to be obtained. The effective interface dipolar and bulk quadrupolar SHG hyperpolarizabilities in the Si1−xGex sample with various Ge concentration profiles are modeled by interpreting the concentration of a component element as the probability of the element occupying an atomic site. On the basis of the developed model, the Ani-RSHG spectra of the as-grown samples with various Ge ratios for each layer and the samples annealed at 850 °C and 950 °C are analyzed to inspect the change in Ge distribution and its gradient in depth. The Ani-RSHG analysis on as-grown samples showed difference in Ge distribution in samples with the multi Si/SiGe structure, which is not well observed in synchrotron X-ray diffraction (XRD) spectra. For the annealed samples, the response to changes in Ge concentration and its gradient in depth reveal the Si/Si1−xGex interface intermixing. Results of high-angle annular dark-field scanning transmission electron microscopy and energy dispersive X-ray spectroscopy agree well with the Ani-RSHG with SBHM findings. Compared with the Raman and synchrotron XRD spectra, the Ani-RSHG with SBHM simulation result demonstrates much better response to changes in compositions of the Si/Si1−xGex stacked multilayered structures, verifying the potential for characterizing the concentration distribution in stacked multilayered thin films for GAA structures.
... Figure 2 shows the absorption coefficient curves with solar spectrum for different mole fractions of Ge in Si 1− Ge heterolayers. The curves are obtained using (8) with consideration that and ph values are 3200 and 50 meV, respectively applicable for SiGe alloys [20]. According to Figure 2, it is observed that absorption SiGe is increased with in Si 1− Ge heterolayers when plotting them against the incident energy. ...
Multijunction solar cells designed from silicon (Si)-germanium (Ge) alloy based semiconductor materials exhibit high theoretical efficiencies (19.6%) compared to the single junction one. The modeling calculations for all solar cells are done by AMPS 1D simulator. The structure of multi-junction i-layer is designed using heterolayers, starting from pure crystalline Si and increase of Ge mole fraction by 25% until pure Ge layer is reached. The top layer has the largest band gap, while the bottom layer has the smallest bandgap. This design allows less energetic photons to pass through the upper layer(s) and be absorbed by the layer below, which increases the overall efficiency of the solar cell. Material parameters required to model the absorber layers are calculated and incorporated in the AMPS 1D simulator for optimizing of solar cell parameter values. Simulation results show that considerable efficiency enhancement can be obtained from the addition of the multi-junction layer.
... Significant improvements in SiGe heteroepitaxy on Si have made SiGe/Si heterojunction photodetectors an important device for both long haul and short-distance light wave network systems operated in the near infrared regions (0.8 to 1.6 μm). In the past few years, various SiGe/Si heterojunction infrared photodetectors have been demonstrated , such as Schottky-barrier, metal–semiconductor–metal (MSM), PIN, avalanche photodiode (APD), and heterojunction phototransistor (HPTs) [1][2][3][4][5][6]. Since the Schottky-barrier, MSM, and PIN photodetectors do not have the internal gain, the sensitivity to the weak input optical power is inferior. ...
An a-Si:H/SiGe/Si punchthrough heterojunction phototransistors (PTHPTs), responding to a wavelength of 850 nm, have been proposed and demonstrated in this work. The dramatic difference between PTHPTs and conventional heterojunction phototransistors is that the base is completely depleted in the PTHPTs, thus a larger optical gain is achieved due to the lack of a neutral base. Furthermore, the use of low-temperature a-Si:H instead of conventional crystalline silicon, a strained SiGe can be preserved at the interface of base and emitter, allowing ultrashallow junctions and abrupt doping profiles. Another advantage is that the a-Si:H can provide large valence-band discontinuity between base and emitter, avoiding photogenerated holes injected from base to emitter, and hence a larger collector current. In addition, we employed a thin Al-coating covered on the surface of emitter to enhance the collection of photogenerated holes. In comparison to the PTHPTS without the thin-Al coating, the optical gain of PTHPTs with thin-Al coating is increased from 922 to 3970 at 5-V bias voltage, responding to a light source of 850 nm with 0.028 mW.
... As shown in Fig. 3, the dark current of devices with 30-and 45-nm a-Si:H caps is saturated at about 0.5-V bias voltage. The density of the dark current is about 4.8 × 10 −8 A/cm 2 for 60-nm a-Si:H capped devices under 4-V reverse-bias voltage, which is much lower than SiGe p-i-n PDs with mesa-and SiO 2 -passivated wall structures having a dark-current density of about 7 × 10 −5 A/cm 2 under the same reverse-bias voltage [20]. Being three orders higher than in our devices, this density indicates good passivation by the a-Si:H used in our studies. ...
SiGe/Si heterojunction infrared Schottky-barrier photodetectors (PDs) with different thicknesses (30-60 nm) of amorphous silicon (a-Si:H) cap layers were successfully fabricated. The SiGe and a-Si:H layers were deposited by using ultrahigh-vacuum chemical vapor deposition and plasma-enhanced chemical vapor deposition systems, respectively. In the fabricated PDs, it was observed that the a-Si:H cap layer can effectively suppress a dark current and that the thicker a-Si:H cap can obtain lower dark current. The lowest dark current was observed in the 60-nm a-Si:H capped PDs. When compared with a capless a-Si:H device, the dark current in the 60-nm a-Si:H capped PD was reduced by a magnitude of 317 at 4-V reverse-bias voltage. However, by increasing the a-Si:H thickness, the photocurrent was reduced. Therefore, a compromise in a-Si:H thickness should be chosen. We discovered that the photo-to-dark-current ratio was enhanced by a factor of 850 for 30-nm a-Si:H capped PDs as compared to that of capless a-Si:H devices. Thus, a PD with a higher noise-rejection ability was achieved by merely inserting a thin a-Si:H layer. Possible mechanisms are discussed in detail by the use of spectrum and band diagrams.
... The large and small detector areas show similar results. The indirect energy gap and phonon energy of the Sil-xGe x multi-layers in each sample can be analysed using the Macfarlane's model to fit the photo current spectra [124][125][126][127]. This approximation is valid for very thin absorbing layers ad«1 with a condition that applies for these samples [125][126][127]. ...
... The indirect energy gap and phonon energy of the Sil-xGe x multi-layers in each sample can be analysed using the Macfarlane's model to fit the photo current spectra [124][125][126][127]. This approximation is valid for very thin absorbing layers ad«1 with a condition that applies for these samples [125][126][127]. Figure 6.5 and 6.6 depicts the square-root of the measured photoresponse for devices from each wafer having areas of 0.042 and 0.0025cm2. ...
p>Si/Si<sub>1-x</sub>Ge<sub>x</sub> multiple quantum well structures are grown by low pressure chemical vapour deposition (LPCVD). The LPCVD systems used were built in-house and are used to produce expitaxial layers at relatively high growth rates. Typically, 10 periods of Si/Si<sub>1-x</sub>Ge<sub>x</sub> quantum wells are grown on <100> silicon substrates at 800°C and at 0.5 Torr. SiGe quantum wells of around 10, 20 or 30 nm are produced with Ge content in the range 6% to 20%. Increasing germane flow is shown to increase the incorporation rate of germanium atoms and at high germanium incorporation levels the Si/Si<sub>1-x</sub>Ge<sub>x</sub> layers are shown to form lens-shaped quantum dots of relatively high germanium content.
Absorption and photoluminescence (PL) measurements are performed to investigate the optical properties and the band structure of the quantum structures. Extended absorption in the near-infrared is observed for the Si/Si<sub>1-x</sub>Ge<sub>x</sub> quantum well samples, with a wavelength cut-off around 1300nm. Doped multi-layer samples indicate additional absorption in the 2μm to 5μm spectral range, due to a free carrier absorption mechanism. Photoluminescence spectra indicate bandgap narrowing due to both increasing germanium composition and strain effects, furthermore, free exciton radiative transitions are observed up to 100K indicating quantum confinement.
p- i -n photodiodes are constructed to form photodetectors incorporating Si/Si<sub>1-x</sub>Ge<sub>x</sub> epilayers. The epitaxial layers grown at 820°C and at 0.5 Torr, consisted sets of ten periods of Si/i<sub>1-x</sub>Ge<sub>x</sub> layers with nominal 6% or 20% germanium content and 10, 20 or 30 nm SiGe thickness providing six main device sets. The I-V characteristics of all devices indicate reliable diode performance. Device photoresponses were studied with a range of bias voltages for wavelengths from 900 to 1500 nm at room temperature. The quantum efficiency in all devices indicates good photodetection extending to 1350 nm in the near-infrared beyond the energy corresponding to the bandgap of silicon.</p
... . 1.1µm and 1.2µm data are extracted from [6]. ...
A strained-SiGe heterojunction bipolar phototransistor is presented for the first time. Theoretical demonstration of the device is recalled. Practical measurements at 940 nm are presented. A dc phototransistor mode responsivity of 1.49 A/W is achieved. Tools are proposed for the opto-microwave behavior analyses of photodetectors. A frequency behavior reaching 32 GHz with a -70 dBm output level and a 200 μW input optical power is demonstrated.
... The literature concerning this point is very scarce and, at the knowledge of the authors, there is no published room temperature measurement's data on the absolute absorption coefficient α of strained SiGe. Nevertheless 90K-measurements are published [6], as well as room temperature spectrum absorption's edge measurement [7], [8]. Hence it is possible to test the validity of the model of absorption presented hereafter. ...
... Best-suited E g300 value for silicon is found to equals 1.09eV. Those values are in good agreement with the literature where phonon energies between 40 and 61meV are given, [7], [8], [9], [10], [14]. Comparison with silicon and germanium spectra's data are shown in Figure 2 at both 77K and 300K temperatures. ...
... In a commonly used first-order approximation, the temperature dependence of the band-gap energy is described with two parameters, α T and β T , which are determined by a linear interpolation of Si and Ge values that are given in Table 1, [8]. Both band-gap reduction due to x and band-gap variation with temperature contribute to the strained-SiGe band-gap energy, as given by equation ( ...
A physical model of the absorption in strained-SiGe on Si layers
based on the one-photon MacFarlane model is investigated. Temperature
variations are included as well as germanium context effect on
parameters of the model. Results are compared to existing data and then
are injected in a numerical-simulation-software. First optical
simulations on strained SiGe photodiode are therefore performed which
open the way to better understanding and optimisations of SiGe-based
optoelectronic devices
... Instead, Si 1x Ge x alloys have the advantage of a relatively high absorption coefficient at these wavelengths. Since the bandgap of Si 1x Ge x can be varied from that of Si to that of Ge, the emission spectrum of this material will cover the wavelength range of interest for optical fiber communication systems, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]22,23 thus creating an opportunity to fabricate waveguide LED's that operate at room temperature. Recently, waveguides, 1-10 photodiodes, [11][12][13][14] and roomtemperature LED's 15 in vertical geometry have been demonstrated. ...
... Since the bandgap of Si 1x Ge x can be varied from that of Si to that of Ge, the emission spectrum of this material will cover the wavelength range of interest for optical fiber communication systems, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]22,23 thus creating an opportunity to fabricate waveguide LED's that operate at room temperature. Recently, waveguides, 1-10 photodiodes, [11][12][13][14] and roomtemperature LED's 15 in vertical geometry have been demonstrated. The main design purpose of these devices is the confinement factor in the active SiGe layer. ...
... So far, there is no unanimity in reported experimental data for the SiGe refractive index that is dependent on the Ge concentration at communication wavelengths. [1][2][3]12,14,[31][32][33] It should be noted that a high optical birefringence may appear as a result of the strain in the SiGe strained-layer waveguides. This in turn may change the refractive index, which is sensitive to the strain state. ...
We analyze theoretically the feasibility of what we believe to be a novel two-dimensional SiGe/Si strained-layer waveguide. The new geometry can be grown by selective epitaxy and has loosened cutoff and critical-thickness restrictions. This geometry could be applied for waveguide-active devices such as LED's, photodetectors, and modulators. Owing to the high cross section of the guided mode, these devices could be easily interfaced in practice with optical fibers. (C) 1999 Optical Society of America [S0740-3232(99)02103-1].
... The initial voltage profile was taken to be the flat-band condition with the valence-band discontinuity at the SiGe-Si interface. The mol fraction of Si Ge was assumed to be 0.2 (bandgap discontinuity 0.17 eV [13], [14]) and the doping of the -doped regions was assumed between 2 and 3 10 cm . The residual doping density in the Si barriers and the other nonintentionally doped regions was assumed to be 10 cm . ...
... By applying an electric field across the well, the confined hole concentration will decrease as (12) where is the initial confined hole concentration and is escape characteristic time given by the thermionic and tunneling escape times . The thermionic escape time is determined by calculating the probability that a carrier will have sufficient thermal energy to overcome the barrier and can be written as (13) where is the hole effective mass, is the well width, is the well barrier height, is the energy eigenvalue, and is the electric field in the well. The tunneling process could be ignored in the first approximation of the escape time calculation as the voltage required for appreciable tunneling is calculated to be beyond the device breakdown voltage. ...
We propose a new type of light modulator at 1.3 and 1.55 μm
using a δ-modulation-doped SiGe-Si multiple-quantum-well
quantum-well structure (δ-MDMQW) integrated in a low-loss
silicon-on-insulator (SOI) waveguide, The structure is embedded in the
intrinsic region of a vertical p-i-n diode realized on SOI substrate. We
present theoretical calculation of the effective index modulation
determined by the variation of the confined hole concentration with an
applied external field. A practical device is proposed and a calculation
of optical modulation efficiency is presented. Estimation of on-off
switching time based on evaluation of characteristic time of emission
from localized levels in quantum wells and RC characteristics of the
device are presented. This device presents the advantage of a broad
optical bandwidth in comparison to the modulators based on
quantum-defined Stark effect, low insertion loss, high-speed (above 1
GHz), and full compatibility with silicon technology
