Ge Codoping Research Articles

CdSe Quantum Dots Enable High Thermoelectric Performance in Solution-Processed Polycrystalline SnSe.

Here, a high peakZTof ≈2.0 is reported in solution-processed polycrystalline Ge and Cd codoped SnSe. Microstructural characterization reveals that CdSe quantum dots are successfully introduced by solution process method. Ultraviolet photoelectron spectroscopy evinces that CdSe quantum dots enhance the density of states in the electronic structure of SnSe, which leads to a large Seebeck coefficient. It is found that Ge and Cd codoping simultaneously optimizes carrier concentration and improves electrical conductivity. The enhanced Seebeck coefficient and optimization of carrier concentration lead to marked increase in power factor. CdSe quantum dots combined with strong lattice strain give rise to strong phonon scattering, leading to an ultralow lattice thermal conductivity. Consequently, high thermoelectric performance is realized in solution-processed polycrystalline SnSe by designing quantum dot structures and introducing lattice strain. This work provides a new route for designing prospective thermoelectric materials by microstructural manipulation in solution chemistry.

Influence of GeO2 Content on the Spectral and Radiation-Resistant Properties of Yb/Al/Ge Co-Doped Silica Fiber Core Glasses.

In this study, Yb/Al/Ge co-doped silica fiber core glasses with different GeO2 contents (0–6.03 mol%) were prepared using the sol–gel method combined with high-temperature sintering. The absorption, fluorescence, radiation-induced absorption, continuous-wave electron paramagnetic resonance spectra, and fluorescence decay curves were recorded and analyzed systematically before and after X-ray irradiation. The effects of GeO2 content on the valence variations of Yb3+/Yb2+ ions, spectral properties of Yb3+ ions, and radiation resistance of Yb/Al/Ge co-doped silica glasses were systematically studied. The results show that even if the GeO2 content of the sample is relatively low (0.62 mol%), it can inhibit the generation of Yb2+ ions with slight improvement in the spectral properties of Yb3+ ions in the pristine samples and effectively improve its radiation resistance. Direct evidence confirms that the generation of trapped-electron centers (Yb2+/Si-E’/Al-E’) and trapped-hole centers (Al-OHC) was effectively inhibited by Ge co-doping. This study provides a theoretical reference for the development of high-performance, radiation-r esistant Yb-doped silica fibers.

Effect of the GeO2 content on the radiation resistance of Er3+ -doped silica glasses and fibers

In this work, Er/Al/Ge co-doped silica glasses with different GeO2 content (0–3 mol%), as well as Ge/Al co-doped silica glasses, are prepared by combining the sol–gel and high-temperature sintering methods. Further, the effects of the GeO2 content on the absorptions and emissions properties, and lifetimes of the glasses before and after 1KGy γ-ray irradiation are compared. The Er/Al/Ge co-doped silica fibers are prepared from a preform produced via modified chemical vapor deposition (MCVD) combined with nano sol-doping. The effects of Ge co-doping on the optical loss and amplifier gain of the Er-doped silica fibers (EDFs) before and after irradiation are also investigated. The related mechanism and species of the γ-ray radiation-induced color centers are revealed via radiation-induced-absorption (RIA) and continuous wave electron paramagnetic resonance (CW-EPR) spectroscopies. The results revealed that co-doping with GeO2 considerably improves the radiation resistance of the glass and exerts a slight effect on the spectral properties of the Er/Al/Ge co-doped silica glasses before irradiation. The RIA and CW-EPR spectra revealed that the aluminum–oxygen hole center (AlOHC) defects reduce with increasing GeO2 content because the intermediaries, the Ge-related oxygen-deficient centers (GeODC(I) and GeODC(II)), exhibit stronger abilities to trap the holes compared with the [AlO4/2]− group. This reduces the RIA level in the visible and near-infrared regions of the Er/Al/Ge co-doped silica glass. The irradiation experiment on the fiber further confirmed that the radiation resistance of EDFs can be considerably improved by Ge co-doping.

Sc, Ge co-doping NASICON boosts solid-state sodium ion batteries' performance

Solid-state sodium ion batteries (SSSIBs) have been proposed to resolve the safety hazards of traditional liquid batteries. The sodium superionic conductor (NASICON), one of the most promising solid electrolyte candidates, has received much attention. However, the practical use of NASICON has been impeded by low ion mobility at room temperature (RT) and poor interfacial connectivity. Here, the improvement of both bulk and grain boundary conductivity has been achieved simultaneously via Sc and Ge co-doping. Bulk conductivity is increased by the Sc-doping, which increases the stability of the rhombohedral phase at RT, and the Ge-doping, which reduces the monoclinic to rhombohedral phase transformation temperature. The highest total conductivity of 4.64 × 10−3 S cm−1 was obtained for the Na3.125Zr1.75Sc0.125Ge0.125Si2PO12 structure. The improvement in conductivity due to the stabilisation of the rhombohedral phase was verified by DFT calculations. Finally, two different solid-state batteries using Na3V2(PO4)3 and Sn4P3@CNT as electrodes display impressive cycling capacities of 98 and 629 mAh g − 1 after 250 cycles, respectively. This co-doping principle also provides a framework to explore multiple-doping for other materials with similar structures.

Calculation of Phase Diagrams and First-Principles Study of Germanium Impacts on Phosphorus Distribution in Czochralski Silicon

Phosphorus (P) is one of the most widely used donor dopants for fabricating a low-resistivity silicon (Si) substrate. However, its volatile nature and the relatively small equilibrium segregation coefficient in Si at the melting temperature of Si impede the efficient and effective growth of low-resistivity Czochralski (CZ) Si single crystal. The primary objective of this work is to theoretically perceive the influence of germanium co-doping on the heavily P-doped Si crystal by means of CALculation of PHase Diagrams (CALPHAD) approaches and density functional theory (DFT) calculations. Phase equilibria at the Si-rich corner of the Si-Ge-P system has been thermodynamically extrapolated based on robust thermodynamic descriptions of involved binary systems, where Si-P and Ge-P have been re-assessed in this work. Phase diagram calculation results indicate that at a given P concentration (e.g. 0.33 at.% P) Ge co-doping lowers the solidification temperature of the Si(Ge, P) alloys, as well as the relevant equilibrium segregation coefficients of P in the doped Si. DFT calculations simulated the formation of (i) monovacancy in Si as well as (ii) solutions of Si(P) and Si(Ge) with one dopant substitutionally inserted in 64- and 216-atom Si cubic supercells. Binding energies were calculated and compared for Ge-Ge, Ge-P and P-P bonds positioning at the first nearest-neighbors (1NN) to the third nearest-neighbors (3NN). P-P bonds have the largest bonding energy from 1NN to 3NN configurations. The climbing image nudged elastic band method (CL-NEB) was utilized to calculate the energy barriers of P 1NN jump in the 64-atom Si cubic supercell with/without a neighboring Ge atom. With Ge present, a higher energy barrier for P 1NN jump was obtained than that without involving Ge. This indicates that Ge can impede the P diffusion in Si matrix.

Effects of co-doping nitrogen and germanium on dislocation gliding in Czochralski silicon: Implication for improving mechanical strength

Improving the mechanical strength of Czochralski (CZ) silicon is of significance for increasing the manufacturing yield of integrated circuits. In this work, we have comparatively investigated the dislocation gliding behaviors in the conventional CZ silicon, nitrogen (N)-doped CZ silicon, germanium (Ge)-doped CZ silicon as well as Ge and N co-doped CZ silicon subjected to the indentations for 30 min at different temperatures in the range of 850–1050 °C with an interval of 50 °C. It is found that the suppressing effect of N-doping on the dislocation gliding is strongest at 950 °C and becomes slightly weakened at higher temperatures, while Ge-doping does not exert a remarkable suppressing effect on the dislocation gliding until the temperature exceeds 950 °C. The co-doping of N and Ge impurities takes both advantages of N- and Ge-doping to suppress the dislocation gliding in CZ silicon at the aforementioned temperatures. More importantly, at 1000 and 1050 °C that are the typical processing temperatures for integrated circuits, the N and Ge co-doping exhibits a stronger suppressing effect on the dislocation gliding in CZ silicon than the single Ge- or N-doping. This indicates that the mechanical strength of CZ silicon in terms of the resistance of dislocation gliding at a high temperature can be further improved by co-doping Ge and N impurities. It is believed that the N-doping can result in the formation of larger grown-in oxygen precipitates and N–O complex-related pinning agents within the dislocations to suppress the dislocation gliding at 850–1050 °C with the strongest suppressing effect at 950 °C, while the suppressing effect of Ge-doping on the dislocation gliding at the temperatures exceeding 950 °C is tentatively ascribed to the formation of Ge–O complexes near the front of the dislocation lines.

Sub-nm Near-Surface Activation Profiling for Highly Doped Si and Ge Using Differential Hall Effect Metrology (DHEM)

Contact resistivity at the metal-semiconductor interface is a strong function of the carrier concentration in the near surface. For next generation 2D/3D MOSFET transistors, industry has been investigating very highly doped materials (>1x1021cm-3) approaching alloy concentrations in Silicon and various Silicon-Germanium materials. All the while, contact development in Ge NMOS has favored co-doping approaches. Regardless of the material system, it is very important to accurately measure near-surface dopant activation. In this paper, we use Differential Hall Effect Metrology (DHEM) implemented on the ALPro™ tool to characterize the activation profiles in both materials. The method employs electrochemical means of reducing the electrically active thickness of a semiconductor film and determining the sheet resistance and mobility of the thinned down layer using Van der Pauw/Hall effect type measurements. By repeating this process and using differential equations, depth profiles of mobility and carrier concentration are obtained [1] at sub-nm resolutions.It is difficult to achieve high n-type dopant activation in Ge. Point defects in Ge are known to behave as acceptor sites and reduce the overall free electron density, particularly near the surface. Minimization of these defects is essential to achieving high performance Ge NMOS. Accurate analysis of dopant activation within 5 nm of the surface is critical to understanding effectiveness of various process steps on improving contact resistance. We have previously published a study on the effect of Ge co-doping with Sb and P on near-surface dopant activation. In Ge with only P-doping it was found that only ~5x1018cm-3 or 5% of the total surface dopants (~1x1020cm-3) were electrically active. With Sb as a co-dopant, the active electron concentration increased to ~2x1019cm-3 with a similar P chemical concentration. Prior work has shown similar increases in activation with co-doping but did not capture the significant decrease in electron concentration by 4x within 10 nm of the surface. Here, we further study the effects of the implantation and annealing processes on near-surface dopant activation in n-type Ge. Samples were prepared by growing 3 µm thick epi-Ge layers on Si substrates. Sample 1 was capped with 20 nm SiO2 and Sample 2 was capped with 20 nm Al2O3 to minimize implant damage and control implant depth. Both samples were implanted first with Sb (dose: 6x1014cm-2, energy: 65 keV) followed by P (dose: 6x1014cm-2, energy: 90 keV). Post-implant anneal was done at 500°C for 10 s in N2 to activate the dopants. ALProTM and SIMS measurements were done to characterize active dopant concentration and total chemical dopant concentration, respectively. The Al2O3 capped sample (Sample 2) showed significantly lower carrier concentration than the SiO2 capped sample (Sample 1) throughout the depth of the profile (Figure 1). Carrier concentration at the surface was lower by nearly an order of magnitude, decreasing from ~2x1019cm-3 to ~2x1018cm-3. Additionally, the peak concentration decreased from 1x1020cm-3 to 5x1019cm-3 at a depth of ~30 nm in both cases. The variations in the carrier profile for the Al2O3 capped sample also indicate greater process variation. SIMS profiles show that there is significant diffusion of Al into the Ge matrix after implant and anneal. Al chemical concentration is 1x1020cm-3 at the Ge surface and steadily decays up to a depth of more than 300 nm. This indicates that there is significant damage caused during the implantation process and the activation anneal is not enough to remove these defects. Al atoms then diffuse from the Al2O3 capping layer into the highly defective Ge substrate. Al is a p-type dopant in Ge and counter-dopes the Sb and P implants to reduce overall electron concentration in Sample 2. It is important to note the high resolution DHEM technique was able to resolve this important phenomenon right near the surface of the material.Additionally, we present early data on very highly phosphorus-doped (~1x1021cm-3) epitaxial silicon thin films grown on Si substrates. In very highly doped Silicon materials, the effect of near-alloy levels of dopant in the matrix on dopant deactivation is not well-known. Samples were obtained with different levels of dopant concentration above ~1x1021cm-3and different anneal temperatures. It was found that near-surface activation in these un-capped samples led to a lowering of activation in the <20nm region from the surface. Extensive post-DHEM metrology (using TEM and SIMS analysis) will also be presented demonstrating control and precision of DHEM data.

(Invited) Differential Hall Effect Metrology (DHEM) Sub-Nm Profiling and Its Application to Dopant Activation in n-Type Ge

With silicon CMOS technology approaching its limits due to continued device scaling, many potential new channel materials have been proposed. Germanium shows considerable promise due to having higher electron and hole mobilities compared to silicon. In addition, the electron and hole mobilities are similar, making it a viable option for CMOS technology. High performance Ge PMOS has been demonstrated, but NMOS has lagged behind due to the difficulty in making low resistance contacts to n-type Ge. Contact resistance is a strong function of the carrier concentration at the semiconductor surface, and it is extremely difficult to achieve high electron activation in Ge. Point defects in Ge are known to behave as acceptor sites and reduce the overall electron activation, particularly near the surface. Minimization of these defects is essential to achieving high performance Ge NMOS. Techniques such as fluorine passivation and co-doping with Sb and P have been shown to reduce the defect density and improve dopant activation, but the impact of these methods in the near-surface regime has largely been uncharacterized. Accurate analysis of dopant activation within 5 nm of the surface is critical to understanding the effectiveness of such processes on improving contact resistance.Differential Hall Effect Metrology (DHEM) is a powerful method that provides dopant activation depth profiles at sub-nm resolution. The method employs electrochemical means of reducing the electrically active thickness of a semiconductor film and determining the sheet resistance and mobility of the thinned down layer using Van der Pauw/Hall effect type measurements. Repeating this process and using differential equations, depth profiles of mobility and carrier concentration are obtained [1].We have previously used the ALProTM tool employing the DHEM technique to study the effect of Ge co-doping with Sb and P on near-surface dopant activation [2]. In Ge with only P-doping, the active dopant concentration was ~5x1018cm-3 at the surface despite the P chemical concentration being ~1x1020cm-3, indicating that only 5% of the implanted dopants were electrically active. With co-doping of Sb and P, the active electron concentration increased to ~2x1019cm-3 with a similar P chemical concentration. Prior work has shown similar increases in activation with co-doping but did not capture the significant decrease in electron concentration by 4x within 10 nm of the surface. Here, we further study the effects of the implantation and annealing process on near-surface dopant activation in n-type Ge. Samples were prepared by growing 3 µm thick epi-Ge layers on Si substrates. Sample 1 was capped with 20 nm SiO2 and Sample 2 was capped with 20 nm Al2O3 to minimize implant damage and control implant depth. Both samples were implanted first with Sb (dose: 6x1014cm-2, energy: 65 keV) followed by P (dose: 6x1014cm-2, energy: 90 keV). Post-implant anneal was done at 500°C for 10 s in N2 to activate the dopants. ALProTM and SIMS measurements were done to characterize active dopant concentration and total chemical dopant concentration, respectively.The Al2O3 capped sample (Sample 2) showed significantly lower dopant activation than the SiO2 capped sample (Sample 1) throughout the depth of the profile (Figure 1). Active electron concentration at the surface was lower by nearly an order of magnitude, decreasing from ~2x1019cm-3 to ~2x1018cm-3. Additionally, the peak concentration decreased from 1x1020cm-3 to 5x1019cm-3 at a depth of ~30 nm in both cases. The variations in the carrier profile for the Al2O3 capped sample also indicate greater process variation. SIMS profiles show that there is significant diffusion of Al into the Ge matrix after implant and anneal. Al chemical concentration is 1x1020cm-3 at the Ge surface and steadily decays up to a depth of more than 300 nm. This indicates that there is significant damage caused during the implantation process and the activation anneal is not enough to remove these defects. Al atoms then diffuse from the Al2O3 capping layer into the highly defective Ge substrate. Al is a p-type dopant in Ge and effectively counter dopes the Sb and P implants to reduce overall electron concentration in the Al2O3 capped sample. It is important to note the high resolution DHEM technique was able to resolve this important phenomenon right near the surface of the material.

The study of oxygen-deficient centers in Al-doped amorphous germanium oxides

Electronic and optical properties of Germanium oxygen-deficient center (GeODC) defect and Al-doped GeODC defect in 96 atoms amorphous GeO2 (a-GeO2) supercells have been investigated. All the 64 oxygen sites in the a-GeO2 configuration have been orchestrated as possible candidates for the construction of 64 different GeODCs. A Ge atom has been substituted by an Al atom in GeODCs to form the Al-GeODCs. It is discovered that the refractive index of a-GeO2 is reduced by GeODC defect, contrary to the situation when Al is doped in GeODC defect. The absorption peak at 5.15 eV is related to GeODC defect. After Al-doping, a new defect state is generated near the top of valence band (TVB), resulting in an absorption peak at 4 eV. The variations of refractive index and optical properties exhibited offer a significant and profound guidance of Al and Ge co-doping in silica optical fiber.

Synergistically improving the thermoelectric performance of In2O3 via a dual-doping and nanostructuring approach

Co-substitution along with nanostructuring is typically employed to optimize thermoelectric transport properties for the development of highly efficient n-type thermoelectric materials. However, an understanding of defect chemistry plays a vital role in choosing the right substituent for the matrix of the parent structure. We investigate the thermoelectric performance of In2O3 via dual doping with Zn and Ge co-substitution. A single-phase structure with nanosized grains has successfully been obtained with Zn and Ge co-substitution even at an 8% doping concentration, using high energy planetary ball milling followed by spark plasma sintering (SPS). Zn and Ge co-doping substantially improved electrical transport by enhancing carrier concentration, which resulted in an increased effective mass with modest carrier mobility achieved sufficiently high power factor value of 9.39 μW cm−1 K−2 at 973 K observed for an 8% doping concentration. Furthermore, reduction of lattice thermal conductivity is observed from the co-substitution because of mass fluctuation scattering of the phonons. The combined effect of dual doping, the selection of the right substituent and phase purity results in an improved figure of merit ZT value of 0.36 at 973 K. This study suggests that In2O3 can be a potential material for thermoelectric applications.

Effects of Ge Co-Doping on P-Related Radiation-Induced Absorption in Er/Yb-Doped Optical Fibers for Space Applications

This study demonstrates that phosphorus-related radiation-induced absorption (RIA) bands such as P-OHC and P1 in erbium/ytterbium-doped optical fibers (EYDFs) are effectively decreased by germanium (Ge) co-doping. The suppression of the generation of both P-OHC during X-ray irradiation of glass preforms and P1 during gamma-ray irradiation of optical fibers was measured for Ge concentrations between 0 wt% and 6.7 wt%. For the 10 krad X-ray irradiation of glass preforms, it was found that the RIA decreased from 5.6 dB/cm to 1.3 dB/cm when the Ge concentration was increased from 0.79 wt% to more than 4.4 wt%. Furthermore, in multimode optical fibers (MMFs) exposed to 100 krad of gamma-ray irradiation, the RIA decreased from 3.7 dB/m to 0.90 dB/m when the Ge concentration was increased from 0.0 wt% to 4.0 wt%, whereas it was 0.35 dB/m for a single-mode optical fiber (SMF) with a Ge concentration of 6.7 wt%. These results demonstrate that Ge concentrations up to 4.4 wt% are strongly correlated with improved radiation tolerance for both glass preforms and optical fibers. This effect was more prominent for SMFs than MMFs and became saturated with excess co-doping in both cases. Therefore, Ge co-doping may represent a good solution for reducing P-related RIA in EYDFs for space applications.

Impact of germanium co-doping on oxygen precipitation in heavily boron-doped Czochralski silicon

We have investigated the impact of germanium (Ge) co-doping on oxygen precipitation (OP) in heavily boron (B)-doped Czochralski (CZ) silicon subjected to low-high two-step anneal without or with the prior high temperature rapid thermal process (RTP). Herein, the Ge concentration is one order of magnitude higher than the B concentration. It is found that the Ge co-doping exhibits the effect of suppression or enhancement on OP in the heavily B-doped CZ silicon without or with the prior RTP. In the case without the prior RTP, the compressive stress introduced by the Ge co-doping compensates the tensile stress arising from the B-doping, which is not beneficial for the growth of oxide precipitates. While, in the case with the prior RTP, the Ge co-doping increases the amount of vacancies introduced by the RTP and, moreover, may enable to generate more heterogeneous nucleation centers of oxide precipitates, thus leading to the enhanced OP in the heavily B-doped CZ silicon.

Rapid synthesis and thermoelectric properties of In0.1Co4sb11Te0.8Ge0.2 alloys via high temperature and high pressure

In0.1Co4sb11Te0.8Ge0.2 skutterudite alloys were synthesized by high temperature and high pressure (HTHP) method, and the effect of the In filling and Te, Ge co-doping atoms on thermoelectric properties was investigated under different pressures. The synthetic time was sharply reduced from a few days to 30 min. A fairly good ZT value of 1.12 at 773 K was obtained due to both the remarkably enhanced power factor and the low thermal conductivity.

First-principles study of Ag2ZnSnS4 as a photocatalyst

By using the first-principles calculation based on density functional theory, we propose some approaches to improving the efficiency for the photocatalyst Ag2ZnSnS4 from a theoretical aspect. Comparing its band edge positions with those of other similar compounds, we find that Cu, Ge codoping can adjust both the band gaps and band edge positions of Ag2ZnSnS4 at the same time, which can optimize its band structure for water splitting. In addition, Ag2ZnSnS4 has a type-Ⅱ band offset with another photocatalyst CuGaSe2. Preparation of its homojunction can also improve their efficiencies of photocatalysis hydrolyzation.

Germanium‐doped Czochralski silicon: a novel material for solar cells

AbstractThe effect of Ge codoping on the light induced degradation (LID) of B doped Czochralski‐silicon (CZ‐Si) was investigated. The rate of degradation under illumination is relatively suppressed in B and Ge codoped Czochralski‐silicon (CZ‐Si) compared to B‐doped CZ‐Si. The Oi concentrations measured by FTIR spectroscopy was decreased as the Ge concentration increased in the Si crystal. The formation of Ge‐VO complex in silicon lattice is considered as a possible reason for the variation in Oi. Moreover, the compressive strain field around the Ge‐VO complex may increase the barrier for O diffusion which limits the formation of fast diffusing O dimmers. As a consequence, the B‐O dimmer (O2i) related defects were relatively suppressed, which causes the suppression of LID effect in B and Ge codoped CZ‐Si. (© 2013 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Lattice constants and optical response of pseudomorph Si-rich SiGe:B

Pseudomorph epitaxial films of Si1−xGex:B were grown on undoped (100) Si for x ≤ 0.026 and the B concentration of 1.3 × 1020 cm−3.The in-plane and out-of-plane lattice constants were determined using the X-ray techniques for 004 symmetric and 224 asymmetric diffraction. The influence of B and Ge co-doping has been detected in reflectance and ellipsometric spectra from infrared to ultraviolet. Free-hole plasma and Fano-type resonances of Si phonons and localized 11B and 10B vibrations have been observed. The spectral shift of E1 electronic transitions has been quantified. We found a simple way to test the variations of Ge content using relative reflectance spectra.

The impact of Ge codoping on the enhancement of photovoltaic characteristics of B-doped Czochralski grown Si crystal

The effect of Ge codoping on minority carrier lifetime in boron (B)-doped Czochralski-silicon (CZ-Si) crystals was investigated. The minority carrier lifetime increased from 110 to 176 µs as Ge concentration was increased from zero to 1 × 1020 cm−3 in B/Ge codoped CZ-Si crystals. Light-induced degradation (LID) experiments showed that B-doped CZ-Si degrades rapidly, while B/Ge codoped CZ-Si degrades more slowly. Moreover, the flow pattern defect (FPD) density of grown-in micro-defects (GMD) in as-grown B/Ge codoped CZ-Si decreased with increasing Ge concentration. From the infrared (IR) absorption studies, it was observed that the interstitial oxygen (Oi) concentration decreased as Ge concentration increased in the crystal. The suppressed LID effect in the B/Ge codoped CZ-Si appears to be related to the low concentration of B-O associated defects, possibly because Ge doping retards the Oi diffusion in addition to the low Oi concentration present (evidenced from IR studies). The mechanism by which the Ge concentration influences the reduction of FPDs and Oi concentration is discussed in terms of Ge-vacancy defect formation during post-growth cooling of the ingots.

The impact of Ge codoping on grown-in O precipitates in Ga-doped Czochralski-silicon

The intensity of the infrared absorption band at 1107 cm −1, related to interstitial oxygen (O i ) concentration, decreased as the Ge concentration increased in Ga and Ge codoped CZ–Si crystals. In contrast, the number of precipitates observed on the etched surfaces of CZ–Si wafers increased as the Ge concentration increased. From an energy dispersive X-ray (EDX) analysis, O was observed to be one of the major components of the precipitates. Moreover, Ge was found as one of the components in the precipitate observed on the heavily Ge (>1×10 18 cm −3) codoped CZ–Si wafers. These results suggest that the grown-in O precipitates increase as the O i concentration decreases when the Ge concentration increases in the Si crystal. The Ge-vacancy ( V) complex in the Si lattice probably acted as a heterogeneous nucleation center and may enhanced the grown-in O precipitates thereby reducing the dissolved O i concentration in the Si lattice.

Effects of Double Substitution with Ge and Te on Thermoelectric Properties of a Skutterudite Compound

Studies have shown that the thermoelectric properties of CoSb3 could be improved by the substitution of group IVB or VIB elements for Sb. However, the substitution volume is limited. To get a better picture of the substitution volume in view of thermoelectric properties, Ge and Te double-substituted skutterudite materials were prepared with the nominal composition of Co4Sb x Ge5.9−0.5x Te6.1−0.5x (x = 11, 10, 9, 8) by the traditional solid-state reaction method and spark plasma sintering, and Rietveld analysis was employed to refine the crystal structure. The results showed that the lattice parameter decreased linearly and the solubility limitations of group IVB and VIB elements were greatly alleviated by the Ge and Te codoping. Besides, the thermoelectric properties were analyzed through measurements of electrical and thermal conductivities as well as room-temperature electrical transport properties. The results showed that the substitution volume of Ge and Te could play an important role in the thermoelectric properties, and a minimum lattice thermal conductivity value of 1.56 W m−1 K−1 was obtained at around 673 K for Co4Sb8Ge1.9Te2.1. Co4Sb11Ge0.4Te0.6 achieved the best figure of merit of 0.89 at around 773 K, which was remarkably improved over that of untreated CoSb3.

Ga segregation during Czochralski-Si crystal growth with Ge codoping

The segregation of Ga during the growth of Czochralski-Si crystals with Ge codoping was investigated. The effective segregation coefficient of Ga in Ga/Ge-codoped Si crystal growth was nearly constant over a wide Ge concentration range, even at high Ge concentrations of about 10 21 cm −3. In contrast, the effective segregation coefficient increased at high B concentrations in Ga/B-codoped CZ-Si crystal growth. The segregation behavior of Ga in Ga/Ge- and Ga/B-codoped CZ-Si crystal growth was theoretically compared. The difference in the segregation coefficients of Ga as a function of the codoped impurity (Ge or B) between the two Si crystals was attributed to a difference in the excess enthalpy due to impurity incorporation into the Si crystal between Ga–Ge pairs and Ga–B pairs The effect of Ge codoping on the minority carrier lifetime in Ga/Ge-codoped CZ-Si crystals was also investigated. The minority carrier lifetime increased with increasing Ge concentration. The higher minority carrier lifetime was associated with a decrease in interstitial oxygen related to D-defects in the Si crystal.