Germanium Alloys Research Articles

Oxidation–Nitridation Mechanism in Eutectic Cr-Silicide Alloy and Its Mitigation by Germanium Alloying

The oxidation and nitridation of the eutectic Cr–Cr3Si alloys during exposures in air was investigated with focus on the detailed mechanism of the attack. Exposures in synthetic air (N2–21%O2), and nitrogen (N2–5%H2) atmospheres revealed inward diffusion of nitrogen as the key mechanism for the nitridation process which was markedly higher in nitrogen compared to that in air. Post-exposure investigations proved selective nitridation of the Cr-solid solution phase in both synthetic air and N2–5%H2 atmosphere. During oxidation in air, a continuous A15 silicide layer (Cr3Si) formed at the oxide–alloy interface inhibiting the internal nitridation. This layer formed exclusively in oxidizing atmosphere as a result of the primary oxidation and outward diffusion of chromium, and dissolution of the Cr-solid solution phase. The barrier character of the A15 phase against nitridation was evident based on microstructural and chemical investigations as well as on thermodynamic considerations. Long-term oxidation results indicated that overtime the protective A15 layer was damaged by the formation porosities and internal oxidation during exposure which led to internal selective nitridation. Additions of germanium (Ge) was found beneficial by supporting the formation of the self-protecting A15 layer with long-term protective behavior against internal nitridation for more than 1000 h.

Dispersion of nonresonant third-order nonlinearities in GeSiSn ternary alloys.

Silicon (Si), tin (Sn), and germanium (Ge) alloys have attracted research attention as direct band gap semiconductors with applications in electronics and optoelectronics. In particular, GeSn field effect transistors can exhibit very high performance in terms of power reduction and operating speed because of the high electron drift mobility, while the SiGeSn system can be constructed using CMOS-compatible techniques to realize lasers, LED, and photodetectors. The wide Si, Ge and Sn transparencies allow the use of binary and ternary alloys extended to mid-IR wavelengths, where nonlinearities can also be employed. However, neither theoretical or experimental predictions of nonlinear features in SiGeSn alloys are reported in the literature. For the first time, a rigorous and detailed physical investigation is presented to estimate the two photon absorption (TPA) coefficient and the Kerr refractive index for the SiGeSn alloy up to 12 μm. The TPA spectrum, the effective TPA wavelength cut-off, and the Kerr nonlinear refractive index have been determined as a function of alloy compositions. The promising results achieved can pave the way to the demonstration of on-chip nonlinear-based applications, including mid-IR spectrometer-on-a-chip, all-optical wavelength down/up-conversion, frequency comb generation, quantum-correlated photon-pair source generation and supercontinuum source creation, as well as Raman lasing.

Approaches to Develop High Capacity and Long-Cycle Life Anodes for Lithium Ion Battery

In this presentation, we report solute strengthening in a series of micrometer silicon (Si)-germanium (Ge) alloy particles, which have not been reported in open literature yet. In addition, we will discuss the role of solvent and binder on the capacity retention in high performance anodes (e.g. Si, Ge, and Si-Ge solid solution). Mastery of strengthening strategies to achieve high-capacity anodes for lithium-ion batteries can shed light on the understanding the nature of diffusion-induced stress and offer an approach to use micro-sized materials with an ultrahigh capacity for large-scale batteries. While the nano-sized materials as anodes show the promise, there is a need to utilize micro-sized materials for large-scale battery applications (e.g. electric vehicle) because of their cost-effective process, high package density, ease to scale-up, and the absence of undesirable side reactions between micro-sized anodes and the electrolyte. Consequently, Si-Ge alloys are of practical importance because the resident defects in solid-solutions can strengthen the materials, thus have a potential to alleviate diffusion-induced stress. Addition of a solute (Ge) into silicon creates a local stress field during the formation of solid solution, which interacts with resident dislocations and subsequently impedes their motion. As a result, an increase in yield stress in silicon-based anodes can be obtained, which are capable of withholding greater stresses to initiate slip and the attendant yielding. Germanium is larger than that of silicon in size, hence when the larger solute atom (Ge) is added to the solvent atoms (Si), a compressive stress is generated in the vicinity of Ge atoms. This local stress field interacts with resident dislocations and subsequently impedes their motion to increase the yield stress in silicon-based anodes. Mechanical properties, e.g. Young’s modulus, of Si-Ge alloys have been studied, particularly in Yonenaga’s series of publications for the alloys at high temperatures (> 500oC). The stress-strain for germanium rich alloy was similar to Ge, likewise silicon-rich alloy similar with Si. The unique behavior occurs in compositions with x ~0.50 at which an athermal stress is in its maximum. Below the athermal stress, dislocations are pinned due to the dynamic interaction between a solute and surrounding dislocations, thus strengthening Si-Ge alloys. These results are consistent with our strain analysis and electrochemical measurements. The synthesis process is facile, cost-effective and easily scalable. Si0.50Ge0.50 exhibits a stable capacity of 1320 mAh/g based on the total mass of the electrode at the current density of 500 mA/g with a capacity retention of 92% after 100 cycles. Isotropic structural changes in germanium and strengthening in solid solution contribute to the stable capacity cycling in micro-sized anodes. In comparison with silicon, the addition of Ge into Si substantially improves the capacity retention, particularly in Si0.50Ge0.50, which is consistent with literature reports that Si/Ge alloy showed a maximum yield stress in Si0.50Ge0.50. More importantly, our very recent work shows that the capacity retention can be further improved by designing the distribution of Ge into Si matrix and selecting proper solvent. When the anode particles have a proper structure and composition, they exhibit a very stable capacity up to a few thousand cycles. In Addition, the fluoroethylene carbonate based solvent plays an important role in yielding a better capacity retention. We will summarize our work by analyzing the necessity for a stable mixed conducting structure in the anode to achieve high capacity and highly stable electrode for lithium ion batteries.

Raman studies of phase and atomic compositions of GeSi nanosystems after pulsed annealing

The phase and elemental compositions of GeSi heterostructures deposited on non-refractory substrates are analyzed by using a non-destructive express technique, i.e., the Raman spectroscopy. It is shown that application of pulsed laser annealing allows one to vary the elemental composition and size of nanocrystals formed from solid alloys of germanium and silicon.

(Invited) Germanium Enrichment for Planar-, Fin- and Nanowire-Channel MOSFETs Made on SOI

1. Introduction Depleted body devices such as FinFETs and Ultra-Thin Body and Buried oxide Fully Depleted Silicon-On-Insulator (UTBB FDSOI) MOSFETs have emerged as architectures of choice for technology nodes where conventional planar bulk devices do not provide enough immunity against short channel effects and variability. Offering unsurpassed electrostatic control of the channel, NanoWire FETs (NWFETs)-based architectures are considered as promising successors for future nodes. In all these depleted-body architectures, the control of active power is a strong requirement. Along with supply voltage scaling, it imposes design-level power management strategies, parasitic capacitance reduction and it calls for the use of high-mobility channel materials. For p-type channels, compressively strained silicon germanium alloys (SiGe) are attractive candidates. When depleted-body devices are fabricated on SOI, local germanium enrichment can convert Si to SiGe. This fabrication sequence starts with the growth of an epitaxial SiGe layer, followed by oxidation. During the latter, the surface of the SiGe layer is converted to silicon dioxide while Ge is segregated to the lower part of the stack, which gradually becomes more Ge-rich. This paper discusses the fabrication of SiGe channel for UTBBSOI MOSFETs, FinFETs and NWFETs. It reviews the key points associated to each architecture and critical aspects related to SiGe thermal budget, critical thickness, growth rate control and crystal quality. Results highlight the interest of NWFETs for future technology nodes. 2. SiGe channel UTBB FDSOI MOSFETs The Ge enrichment technique was initially developed for the planar FDSOI architecture and in that context, it was shown that high quality uniform SiGe films can be fabricated by alternating oxidizing and diffusion steps. For a SiGe/Si initial stack of given thickness and composition, the enrichment thermal budget needs to be significantly different when it is performed on SOI or on tensile SOI (sSOI). In the last case, the film initial tensile strain slows Ge diffusion (Fig. 1-a), which can lead to Ge pile up and defect formation if process temperature is too high with respect to the peak concentration (Fig. 1-b). Defect-free SiGe layers can be obtained on sSOI by using longer diffusion steps and reducing process temperature (Fig. 1-c). 3. SiGe-channel FinFET Although Ge enrichment can produce fully-strained layers, the patterning of SiGe blanket film into finite-dimension active areas yields elastic stress relaxation. This feature is particularly attractive for the fabrication of SiGe channel FinFETs where channel configuration results in longitudinal uniaxial compression, which is most favorable to hole transport. However, this processing sequence involves the elaboration of a thick blanket SiGe layer (through Ge enrichment and epitaxial thickening). Even with optimized processing, for a targeted Fin height (SiGe thickness) of 35 nm, significant crystal quality degradation is observed by X-Ray Reciprocal Space Mapping for {113} (RSM) when the Ge fraction approaches 50% (Fig. 2-a), in agreement with literature. To overcome this limit, Ge enrichment of already patterned Si Fins was investigated. This sequence relieves the limits set by SiGe critical thickness in the vertical direction, but it also constricts the pre-enrichment SiGe growth conditions. If SiGe growth rate is strongly dependent on crystal orientation, the final Fin profile is degraded (Fig. 2-b). In contrast, Fin profile can be maintained (Fig. 2-c) when uniform SiGe thickness can be achieved on Fin sidewalls (Fig. 2-d). RSM shows that Fins with up to 50% Ge fraction exhibit no significant relaxation (Fig. 2-e). This approach is expected to be most beneficial for tall Fins. 4. SiGe-channel NWFETs W-gate NWFETs were fabricated in a gate first scheme (Fig. 3-a). This configuration combines the respective benefits of SiGe channel FDSOI MOSFETs and FinFETs in terms of SiGe crystal stability [5] and uniaxial strain. With this and excellent electrostatic integrity, significant mobility gains are demonstrated down to a gate length of 14nm (Fig. 3-b), paving the way for future energy-efficient systems. 5. Acknowledgment Part of these results was obtained in a Joint Development Program between IBM, STMicroelectronics and LETI CEA. Figure 1

Thermoelectric Properties of Silicon Germanium Alloy Nanocomposite Fabricated by Mechanical Alloying and Spark Plasma Sintering

High dense p-type Si95Ge5 doped with nanoSi70Ge30B5particles thermoelectric materials were firstly fabricated by mechanical alloying (MA) and spark plasma sintering (SPS) method. The effects of different nanoSi70Ge30B5 doping content on the thermoelectric and phase properties were studied. A dimensionless thermoelectric figure-of-merit (ZT) of 0.47 at 710K in p-type nanocomposite bulk silicon germanium (SiGe) alloys is achieved. The enhancement of ZT is due to a large reduction of thermal conductivity caused by the increased grain boundaries of the numerous nanograins that effectively scatter long wavelength phonons.

Numerical Analysis on Electrical Measurements of Multi-Junction Silicon and Germanium Alloy Based Thin-Film Solar Cell

Numerical Analysis on Electrical Measurements of Multi-Junction Silicon and Germanium Alloy Based Thin-Film Solar Cell

Lattice Thermal Conductivity of the Binary and Ternary Group-IV Alloys Si-Sn, Ge-Sn, and Si-Ge-Sn

Being a good thermoelectric material is a balancing act between high electrical conductivity $\ensuremath{\sigma}$ and low thermal conductivity $\ensuremath{\kappa}$, because both quantities depend directly on the flow of electrons. Fortunately, $\ensuremath{\kappa}$ $a\phantom{\rule{0}{0ex}}l\phantom{\rule{0}{0ex}}s\phantom{\rule{0}{0ex}}o$ depends on lattice phonons, so this contribution can be cut---for example, by scattering from randomly distributed heavy atoms. The authors' calculations show that adding tin to alloys of silicon and germanium should yield quite good thermoelectrics, especially in thin-film systems.

Solution Synthesis, Surface Passivation, Optical Properties, Biomedical Applications, and Cytotoxicity of Silicon and Germanium Nanocrystals.

Silicon and germanium nanocrystals (NCs) are attractive materials owing to their unique size and surface-dependent optical properties. The optical properties of silicon and germanium NCs make them highly suitable for a range of applications, including bioimaging, light-emitting diodes, and solar cells. In this review, the solution synthesis, surface passivation, optical properties, biomedical applications, and cytotoxicity of silicon and germanium NCs are compared and contrasted. Over the last 10 years, synthetic protocols have improved considerably, with size control readily achieved. Investigations have begun into a range of silicon and germanium nanostructures, including doped, alloy, and metal-semiconductor hybrid NCs, which represent the next generation of silicon and germanium nanomaterials. Silicon and germanium NCs are actively researched for a wide array of biomedical applications, including, long-term in vivo cellular imaging, fluorescent nanocarriers for drug delivery, and as contrast agents for magnetic resonance imaging (MRI). Cytotoxicity studies have shown the low toxicity of Si NCs, while demonstrating that Ge NCs are less toxic than CdSe NCs at similar concentrations, giving these materials a strong future in nanomedicine applications.

Large reduction in thermal conductivity for SiGe alloy nanowire wrapped with a Ge nanoparticle-embedded SiO2 shell

We demonstrate silicon germanium (SiGe) alloy nanowires (NWs) with Ge nanoparticles (GeNPs) embedded in a SiO2 shell as a material for decreasing thermal conductivity. During thermal oxidation of SiGe NWs to form SiGe–SiO2 core–shell structures, Ge atoms were diffused into the SiO2 shell to relax the strain in the SiGe core, and agglomerated as a few nanometer-sized particles. This structure leads to a large reduction in thermal conductivity due to the GeNP–phonon interaction, while electrical conductivity is sustained because the core of the SiGe alloy NW provides a current path for the charged carriers. The thermal conductivity of the SiGe alloy NWs wrapped with a GeNP-embedded SiO2 shell is 0.41 W m−1 K−1 at 300 K.

Micro-Sized Si-Ge Solid Solutions As Advanced Materials for High Capacity and Long-Cycle Life Anodes for Lithium Ion Battery

Mastery of strengthening strategies to achieve high-capacity anodes for lithium-ion batteries can shed light on the understanding the nature of diffusion-induced stress and offer an approach to use micro-sized materials with an ultrahigh capacity for large-scale batteries. While the nano-sized materials as anodes show the promise, there is a need to utilize micro-sized materials for large-scale battery applications (e.g. electric vehicle) because of their cost-effective process, high package density, ease to scale-up, and the absence of undesirable side reactions between micro-sized anodes and the electrolyte. Consequently, Si-Ge alloys are of practical importance because the resident defects in solid-solutions can strengthen the materials, thus have a potential to alleviate diffusion-induced stress. Addition of a solute (Ge) into silicon creates a local stress field during the formation of solid solution, which interacts with resident dislocations and subsequently impedes their motion. As a result, an increase in yield stress in silicon-based anodes can be obtained, which are capable of withholding greater stresses to initiate slip and the attendant yielding. Here, we report solute strengthening in a series of silicon (Si)-germanium (Ge) alloy particles, which have not been reported in open literature yet. Germanium is larger than that of silicon in size, hence when the larger solute atom (Ge) is added to the solvent atoms (Si), a compressive stress is generated in the vicinity of Ge atoms. This local stress field interacts with resident dislocations and subsequently impedes their motion to increase the yield stress in silicon-based anodes. Mechanical properties, e.g. Young’s modulus, of Si-Ge alloys have been studied, particularly in Yonenaga’s series of publications for the alloys at high temperatures (> 500oC). The stress-strain for germanium rich alloy was similar to Ge, likewise silicon-rich alloy similar with Si. The unique behavior occurs in compositions with x ~0.50 at which an athermal stress is in its maximum. Below the athermal stress, dislocations are pinned due to the dynamic interaction between a solute and surrounding dislocations, thus strengthening Si-Ge alloys. These results are consistent with our strain analysis and electrochemical measurements. The synthesis process is facile, cost-effective and easily scalable. Si0.50Ge0.50 exhibits a stable capacity of 1320 mAh/g based on the total mass of the electrode at the current density of 500 mA/g with a capacity retention of 92% after 100 cycles. Isotropic structural changes in germanium and strengthening in solid solution contribute to the stable capacity cycling in micro-sized anodes. In comparison with silicon, the addition of Ge into Si substantially improves the capacity retention, particularly in Si0.50Ge0.50, which is consistent with literature reports that Si/Ge alloy showed a maximum yield stress in Si0.50Ge0.50. More importantly, our very recent work shows that the capacity retention can be further improved by designing the distribution of Ge into Si matrix and selecting proper solvent. When the anode particles have a proper structure and composition, they exhibit a very stable capacity up to a few thousand cycles. In Addition, the fluoroethylene carbonate based solvent plays an important role in yielding a better capacity retention. We will summarize our work by analyzing the necessity for a stable mixed conducting structure in the anode to achieve high capacity and highly stable electrode for lithium ion batteries.

Electrolytic Formation of Crystalline Silicon/Germanium Alloy Nanotubes and Hollow Particles with Enhanced Lithium-Storage Properties.

Crystalline silicon(Si)/germanium(Ge) alloy nanotubes and hollow particles are synthesized for the first time through a one-pot electrolytic process. The morphology of these alloy structures can be easily tailored from nanotubes to hollow particles by varying the overpotential during the electro-reduction reaction. The continuous solid diffusion governed by the nanoscale Kirkendall effect results in the formation of inner void in the alloy particles. Benefitting from the compositional and structural advantages, these SiGe alloy nanotubes exhibit much enhanced lithium-storage performance compared with the individual solid Si and Ge nanowires as the anode material for lithium-ion batteries.

Electrolytic Formation of Crystalline Silicon/Germanium Alloy Nanotubes and Hollow Particles with Enhanced Lithium‐Storage Properties

AbstractCrystalline silicon(Si)/germanium(Ge) alloy nanotubes and hollow particles are synthesized for the first time through a one‐pot electrolytic process. The morphology of these alloy structures can be easily tailored from nanotubes to hollow particles by varying the overpotential during the electro‐reduction reaction. The continuous solid diffusion governed by the nanoscale Kirkendall effect results in the formation of inner void in the alloy particles. Benefitting from the compositional and structural advantages, these SiGe alloy nanotubes exhibit much enhanced lithium‐storage performance compared with the individual solid Si and Ge nanowires as the anode material for lithium‐ion batteries.

The External Crystal Structure and Electronic Structure are Simulated about Ge<sub>0.6</sub>Si<sub>0.4</sub> Quantum Dots

The alloy Ge0.6Si0.4 quantum dots were studied by using density functional theory. The change of the electronic structure of each crystal which grown in different simulation temperature condition were investigated by molecular dynamics simulation method. The results indicate that quantum dots of silicon germanium alloy occupy the narrow band gap of each crystal face from low to high temperature conditions. Since the atomic density and crystal configuration is different, the band gap values are relatively different. The mechanism of dielectric constant transition is well explained based on the inter-band and in-band shift of band structure.

On the thermoelectric properties and band gap of silicon–germanium alloys in the high-temperature region

For n- and p-type Si0.85Ge0.15 alloys, the thermoelectric properties (thermopower, resistivity, thermal conductivity, and thermoelectric efficiency) are determined in the range from room temperature to 1200°C. The measurements are carried out with an upgraded device [1] by absolute and steady-state methods with thermal screens. The device is upgraded to extend the working-temperature range to ~1500 K. On the basis of these data, the energy-related capabilities of the alloy are estimated; the thermal band-gap width is calculated in the temperature range of ~1300–1400 K.

Porosity as a function of stoichiometry and implantation temperature in Ge/Si1−xGex alloys

The development of porosity in single-crystal germanium and silicon-germanium alloys (c-Si1−x Gex) of (100) orientation was studied under bombardment with 140 keV Ge− ions over a wide range of temperatures (−180 to 400 °C) and ion fluences up to 1 × 1018 ions/cm2. The surface swelling and morphology were investigated using multi-characterization techniques including optical profilometry, transmission electron microscopy, and scanning electron microscopy. The initiation of porosity and the evolution of the near-surface microstructure strongly depend on the ion fluence, the irradiation temperature, and the stoichiometry of the substrate. Significant results and new findings include: (i) the fact that, over the entire temperature and stoichiometry range, porosity is only developed once the substrate is rendered amorphous; (ii) with increasing Si content in the alloy, the onset of porosity is pushed to higher fluences; (iii) porosity is observed for Si contents in the alloy up to 23% but not higher under the irradiation conditions used; and (iv) in all cases the initiation of porosity was observed to occur at the surface of the amorphous alloy above a threshold fluence. This last result strongly suggests that the mechanism for initiation of porosity is via preferential vacancy segregation and clustering at the surface of the amorphous alloy. Particularly at elevated temperatures, preferential sputtering of the Si-Ge atomic species in the alloy also plays an important role in developing the surface topography and porosity in alloys. Such effects are discussed along with the implications of our results for mechanisms of porosity in Ge and its alloys.

Development of Metallic Magnetic Calorimeters with a Critical Temperature Switch

We report on the progress in the development of meander-shaped metallic magnetic calorimeters (MMCs) with a critical temperature switch. A niobium meander-shaped coil in an MMC is arranged to form a superconducting loop. It is to measure the change in magnetization and to apply a persistent current that magnetizes the MMC sensor material. In this work, part of the superconducting loop is fabricated with another superconducting material with its transition temperature ( $$T_\mathrm{C}$$ ) lower than that of niobium. A persistent current can be injected in the loop while reducing the temperature from above to below the $$T_\mathrm{C}$$ of the switch. Aluminum (Al) wires and an alloy of molybdenum and germanium (MoGe) were tested as critical temperature switch. The test with the Al switch demonstrated the temperature switch concept for meander-shaped MMCs that require a large field current. Microfabricated MoGe switches showed a $$T_\mathrm{C}$$ near 4.3 K, but only 7 mA of persistent current could be charged due to MoGe film discontinuity. This issue requires further improvement in the fabrication procedure.

Examination of phonon deformation potentials for accurate strain measurements in silicon–germanium alloys with the whole composition range by Raman spectroscopy

The phonon deformation potentials (PDPs), p and q, of Si1−xGex with the whole range of the Ge concentration x were examined in detail in pursuit of accurate strain measurements by Raman spectroscopy. An oil-immersion Raman technique was adopted to extract the PDPs of Si1−xGex, in which a complex sample preparation process or a stress-introduction device is not necessary. The strain-shift coefficients bLO and bTO, which can be calculated using the obtained PDPs, were compared with the values in the literature, and we suggested which values were best for application to accurate strain measurements. Ab initio calculation was also performed to understand the behavior of the PDPs throughout the whole range of x in Si1−xGex.

Molecular dynamics simulations of thermal transport in isotopically modulated semiconductor nanostructures

AbstractIn this paper, we investigate the effect of isotopic modulation on the thermal conductivity of semiconductor nanostructures. The isotope doping is of particular interest for the application of semiconductors as thermoelectric materials as it leaves the electronic properties practically unaffected while the phononic transport is retarded. This approach could increase the figure of merit of thermoelectric generators by decreasing the thermal conductivity of semiconductors. We use non‐equilibrium molecular dynamics simulations to examine thermal transport in isotopically engineered semiconductors. The temperature profiles along the sample region deduced from the simulations allow the extraction of thermal conductivities. The reliability of the MD‐predicted thermal conductivities is studied by analyzing the influence of the input parameters on the results. The first set of samples are isotopically modified silicon samples. The influence of temperature, isotopic composition, and ordering of isotopic defects on the thermal conductivity of silicon is studied. The second material system under investigation is silicon germanium alloys. The influence of isotopic modulation on the thermal conductivity of Si–Ge alloys is examined for varying chemical composition. The thermal conductivities predicted by MD are compared to results derived from the solution of the Boltzmann transport equation in the relaxation time approach.

Numerical simulation of silicon heterojunction solar cells with Si/Si1-xGex quantum wells

Heterojunction with intrinsic thin-layer (HIT) solar cells attract attention due to their high open circuit voltage and stable performance. However, short circuit current density is difficult to improve due to light losses of transparent conductive oxide and hydrogenated amorphous silicon passivation (a-Si:H) layer and low absorption coefficient of crystalline silicon (c-Si). Silicon germanium alloy (Si/Si1-xGex) quantum wells and quantum dots are capable of improving low light utilization by strong optical absorption in the infrared region. In this article, opto-MoS2of the HIT solar cells integrated with Si/Si1-xGex quantum wells (HIT-QW) as a surface absorber are investigated by numerical simulation with Technology Computer Aided Design (TCAD). The influences of germanium content on the MoS2of HIT solar cells with long carrier lifetimes of Si1-xGex layers (p*) and defect-free a-Si:H/c-Si interface are investigated at first. The simulation results indicate that optical utilization in the infrared region is enhanced with the increase of germanium fraction, while open circuit voltage degrades due to the decreasing of the energy band gap of Si1-xGex, radiative recombination and auger recombination mechanism in the Si/Si1-xGex quantum wells. And the conversion efficiency reaches a maximum value at a germanium fraction of 0.25 then drops distinctly. When the germanium fraction increases from 0 to 0.25, the short circuit current density increases from 34.3 mA/cm2 to 34.8 mA/cm2, while the open circuit voltage declines from 749 mV to 733 mV. Hence, the conversion efficiency increases from 21.5% to 21.7% due to the fact that the enhancement of short circuit current density compensates for the reduction of open circuit voltage. When the germanium content increases to more than 50%, a serious open circuit voltage loss of more than 130 mV associated with the energy band gap loss of Si1-xGex arises in the HIT-QW solar cells, which indicates that the dominating carrier transport mechanism changes from shockley diffusion to recombination in the Si/Si1-xGex quantum wells. Subsequently, the influences of interface defects at a-Si:H/c-Si interface and bulk recombination centers in the Si/Si1-xGex quantum wells are discussed. Both interface holes at a-Si:H/c-Si interface and bulk holes in Si1-xGex quantum wells can be recombined through the interface defects at a-Si:H/c-Si interface and bulk recombination centers in the Si/Si1-xGex quantum wells, respectively, which restricts the position of hole fermi level in the open circuit condition. When the germanium fraction increases, the influence of interface defects at a-Si:H/c-Si interface becomes weak on the degradation of open circuit voltage compared with the significant influence of the bulk trap centers. Moreover, p* of longer than 510-5 s is necessary for the retention of electrical performance of HIT-QW solar cells by the simulation. Based on this research, high-efficiency HIT solar cells can be achieved by incorporating high-quality Si/Si0.75Ge0.25 quantum wells, which also requires the impactful passivation of a-Si:H/c-Si interface.