Total Ge Content Research Articles

Surface treatments of CdGeAs2 single crystals

The performances of second harmonic generation (SHG) and optical parametric oscillator (OPO) in CdGeAs2 crystal are strongly influenced by surface quality. In this paper, the surfaces of samples were treated by mechanical polishing (MP), chemical polishing (CP), chemical–mechanical polishing (CMP) and CP following CMP closely (CMP + CP). Then, the surface state was characterized by optical microscopy (OM), scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). AFM measurements show that an ultra-smooth surface is achieved after CMP + CP treatment and the roughness value is 0.98 nm. Meanwhile, the roughness of the surfaces treated by MP, CP and CMP are 4.53, 2.83 and 1.38 nm, respectively. By XRD rocking curves, the diffraction peak which belongs to the wafer treated by CMP + CP is the highest in intensity and best symmetrical in shape. XPS analysis indicates that Ge4+ proportions of GeO2 in total Ge content of CdGeAs2 wafers’ surface after MP, CP, CMP and CMP + CP treatment are 27.6%, 42.8%, 6.1% and 30.3%, respectively.

ERRATUM: "BASE COMPOSITION EFFECTS STUDY ON NBR CURRENT AND CURRENT GAIN IN SiGe HBT"

In present study, SiGe Hetero-junction Bipolar Transistors (HBTs) performances are discussed based on both TCAD and analytical evaluations of the heavily doped base. It is demonstrated that neutral base recombination (NBR) current has significant effects on base current and hence current gain. An optimized Ge profile for 20 nm wide base of understudy structure, with 16% Germanium at EB edge and 24% at CB edge is concluded analytically, which improves DC and high frequency behavior. TCAD simulations reveal that for the specific structure and proposed profile, current gain is about 3500. It also exhibits ft and fmax about 325 GHz and 192 GHz, respectively. In the next section for the first time, a comprehensive study of early voltage variation based on total Ge content and Ge grading in base is also presented. Forced base-emitter voltage and forced base current configurations are studied separately. NBR current has been analyzed under two different configuration and prospective guidelines are indicated.

BASE COMPOSITION EFFECTS STUDY ON NBR CURRENT AND CURRENT GAIN IN SiGe HBT

In present study, SiGe Hetero-junction Bipolar Transistors (HBTs) performances are discussed based on both TCAD and analytical evaluations of the heavily doped base. It is demonstrated that neutral base recombination (NBR) current has significant effects on base current and hence current gain. An optimized Ge profile for 20 nm wide base of understudy structure, with 16% Germanium at EB edge and 24% at CB edge is concluded analytically, which improves DC and high frequency behavior. TCAD simulations reveal that for the specific structure and proposed profile, current gain is about 3500. It also exhibits ft and f max about 325 GHz and 192 GHz, respectively. In the next section for the first time, a comprehensive study of early voltage variation based on total Ge content and Ge grading in base is also presented. Forced base-emitter voltage and forced base current configurations are studied separately. NBR current has been analyzed under two different configuration and prospective guidelines are indicated.

Self-Assembly of Nanohills in Si1−xGex/Si Hetero-Epitaxial Structure Due to Ge Redistribution Induced by Laser Radiation

The study is focused on formation and optical properties of nanostructures induced by laser radiation on the surface of Si1-xGe(x)/Si hetero-structures. Formation of self-assembling nanohills induced by irradiation of nanosecond Nd:YAG laser pulses on the Si0.7Ge0.3/Si hetero-epitaxial structures is reported. The atomic force microscope study of the irradiated surface morphology has shown a start of nanohills formation after laser irradiation of the intensity I = 7.0 MW/cm2. The huge "blue shift" of photoluminescence spectra with maximum intensity in region of 700-800 nm (1.76-1.54 eV) is explained by the quantum confinement effect in the nanohills. The maximum of this photoluminescence band slightly shifts to shorter wavelengths with the increase of the intensity of laser pulses used for sample treatment. Appearance of the 300 cm(-1) Ge-Ge vibration band in Raman scattering spectra for sample irradiated with I = 20.0 MW/cm2 is explained by Ge phase formation. Formation of the Ge-rich phase is explained by localization of Ge atoms drifting toward the irradiated surface under the thermal gradient due to strong absorption of laser radiation. Ellipsometric data confirm appearance of Ge-rich phase precipitates amounting to 7.1%, 6.4% of the total Ge content induced by laser radiation of intensities I1 = 20.0 MW/cm2, I2 = 7.0 MW/cm2 respectively.

Prediction of body weight and empty body composition using body size measurements in lactating dairy cows

Body composition and live animal measurements of Holstein–Friesian lactating dairy cows ( n = 146) were obtained from a large herd to represent a range of animal factors including parity, live weight (LW), body condition score (BCS), milk yield and stage of lactation. Live animal measurements were recorded 3 or 4 days prior to slaughter, including LW, BCS, milk yield, heart girth, belly girth, withers height and length. The objective was to develop prediction equations for body weight and component mass from body size measurements and other live animal data. All body size measurements were positively ( P < 0.001) related to LW, empty body (EB) weight (EBW), carcass weight and EB masses (kg) of lipid, CP, DM, water and ash and total GE content (MJ). The correlation coefficients ( r) in these relationships were highest with heart girth (0.62 to 0.88), followed by belly girth (0.52 to 0.88) and length (0.51 to 0.83) and lowest with withers height (0.35 to 0.69). Heart girth was therefore selected as the primary predictor and a number of equations were then developed for prediction of body weight and EB mass, with the effect of parity or stage of lactation removed, where appropriate. All relationships were significant ( P < 0.001) and each predictor had a significant effect on the relationship ( P < 0.05). The adjusted R 2 values in the linear/quadratic relationships of heart girth with body weight and EB masses ranged from 0.53 (lipid mass) to 0.78 (LW). Addition of a range of other live animal variables (belly girth, length and BCS) to support heart girth significantly improved all relationships, with the Cp statistic and RMSPE (root mean square prediction error) values considerably reduced and adjusted R 2 values increased. These equations were evaluated through internal validation, by developing a range of similar new equations from two thirds of the present data and then validating these new equations with the remaining one third of data. The validation revealed a high prediction accuracy for LW, EBW, carcass weight and EB masses of CP, water and DM, a relatively good accuracy for EB lipid mass and total GE content, and a relatively poor accuracy for EB ash mass. In conclusion, body size measurements can be used together with other live animal factors to accurately predict body weight and EB component mass of lactating dairy cows. These equations provide an alternative approach to estimate body weight and component mass of lactating dairy cows.

Effect of Ge content and profile in the SiGe base on the performance of a SiGe/Si heterojunction bipolar transistor

In this paper, the effects of Ge content and profile shape on the performance of a SiGe-based heterojunction bipolar transistor (HBT) are investigated. The common-emitter current gain, the early voltage, and the transit time of SiGe HBTs are calculated and computed for different Ge profiles as well as the total Ge content in the base, considering uniform base-doping. Then the effects of the above on the cutoff frequency fτ and the maximum oscillation frequency fmax of the HBT are shown. It is seen that both the forward current gain and the transit time decrease with the change in profile from box to triangle, but the early voltage increases with a similar change. The increase of Ge content for the same profile results in a decrease of transit time. From the analysis, a large increase in fτ and fmax can be predicted with a suitable choice of Ge profile and the total Ge content in the base. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 47: 247–254, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21138

Profile design considerations for minimizing base transit time in SiGe HBT's

A unified closed form analytical model for base transit time of SiGe HBT's for uniform and exponential base dopant distributions with different Ge profiles in the base (e.g., box, trapezoidal, triangular) is reported. The model is subsequently used to study the design of Ge profile for different base doping profiles, including that of epitaxial base transistors. Consistent with the reported results, our unified model predicts that beyond a certain total Ge content, there is very little reduction in /spl tau//sub b.SiGe/. It is further demonstrated that the trapezoidal Ge profile with X/sub T//spl sim/0.8W/sub B/ gives near optimal base transit time for all doping profiles considered. Our analysis shows that 1) for a given base width and intrinsic base resistance, the exponential base doping profile with Ge yields the least value of /spl tau//sub b, SiGe/ and 2) for a given peak base doping concentration and the intrinsic base resistance, the uniform base doping with Ge gives minimum /spl tau//sub b, SiGe/. Also, the need for keeping the total base Ge content constant while optimizing the Ge profile in the base is emphasized by showing that a false minimum for /spl tau//sub b, SiGe/ may appear if the total Ge content is not kept constant.

Time-of-flight medium energy ion scattering study of epitaxial [formula omitted] superlattice structures

The ability to determine structural and compositional information from the sub-surface region of a semiconductor material has been demonstrated using a new time-of-flight medium energy ion scattering (ToF-MEIS) system. A series of silicon-silicon/germanium ( Si Si 1 − x Ge x ) heterostructure and multilayer samples, grown using both solid source molecular beam epitaxy (MBE) and gas source chemical vapour deposition (CVD) on Si(100) substrates, have been investigated. These data indicate that each individual layer of Si 1 − x Ge x ( x ∼ 0.22) in both 2 and 3 period samples, can be uniquely identified with a resolution of approximately 3 nm. A comparison of MBE and CVD grown samples has also been made using layers with similar structures and composition. ToF-MEIS showed that the MBE grown samples exhibit a much higher Ge concentration per layer than CVD grown samples. Surface segregation of Ge was observed for the MBE grown samples, but appears to be suppressed in the case of CVD grown samples. These data indicate the ability of ToF-MEIS to probe the differences in the kinetics associated with Ge incorporation and segregation between the two techniques. The total Ge content of each sample was confirmed independently using conventional Rutherford backscattering spectrometry (RBS).

The mineralogical deportment of germanium in the Clarksville Electrolytic Zinc Plant of Savage Zinc Inc.

A mineralogical study was carried out on the neutral leach residue and weak acid leach residue generated from Gordonsville zinc concentrate at the Clarksville Electrolytic Zinc Plant of Savage Zinc Inc. The intent was to characterize the mineral forms and associations of germanium. The Gordonsville zinc concentrate consists mostly of sphalerite which has a solid solution Ge content of ~400 ppm; the sphalerite is the dominant, if not only, Ge carrier in the concentrate. The neutral leach residue consists principally of iron gel-silica gel, ZnO, and basic zinc sulfate, (Zn,Cu)4(SO4)(OH)6·4H2O, together with minor amounts of ZnFe2O4, sphalerite, Zn2SiO4, Zn-Fe-Pb silicate, and PbSO4, as well as traces of quartz, silicates, Pb-K jarosite solid solution, Fe2O3, and FeO·OH. The major Ge carrier is the iron gel-silica gel phase, but modest amounts of Ge are present in the ZnO, ZnFe2O4, sphalerite, and Zn-Fe-Pb silicate phases. The weak acid leach residue consists mostly of iron gel-silica gel, ZnFe2O4, PbSO4, Pb-K jarosite, Zn-Fe-Pb silicate, and quartz. The major Ge carrier is the iron gel-silica gel phase which contains up to 1.7 pct Ge and accounts for ~70 pct of the total Ge content of this residue. The remaining Ge is carried by the Zn-Fe-Pb silicate, ZnFe2O4, and some of the rare Mn-Pb-Fe oxide phases.

Probing the interfacial and sub-surface structure of Si/Si1−xGex multilayers

The ability to determine structural and compositional information from the sub-surface region of a semiconductor material has been demonstrated using a new time-of-flight medium energy ion scattering spectroscopy (ToF-MEISS) system. A series of silicon–silicon/germanium (Si/Si1−xGex) heterostructure and multilayer samples, grown using both solid source molecular beam epitaxy (MBE) and gas source chemical vapor deposition (CVD) on Si(100) substrates, have been investigated. These data indicate that each individual layer of Si1−xGex (x∼0.22) in both two- and three-period samples, can be uniquely identified with a resolution of approximately 3 nm. A comparison of MBE and CVD grown samples has also been made using layers with similar structures and composition. The total Ge content of each sample was confirmed using conventional Rutherford backscattering spectrometry.

Optimum germanium profile for SiGe base HBTs

The thermal stability of an SiGe base HBT is closely related to the integrated Ge content in the base. It is therefore appropriate to consider what form the Ge profile should take to minimise the base transit time τB for a given total Ge content. It is shown that a linear increase in Ge content from the base-emitter to the base-collector junction is required to minimise τB.