Ge Wafers Research Articles

Characterisation of the Femtosecond Laser Micro-Grooving Process for Germanium Substrates

An experimental study is reported to characterise the femtosecond (FS) laser grooving process for Germanium (Ge) substrates. The effects of process parameters, including laser fluence, pulse repetition rate and scan speed, on the groove characteristics, material removal rate (MRR) and heat affected zone (HAZ) size are discussed. It is shown that with properly selected process parameters, high quality micro-grooves can be obtained on Ge wafers. Recommendations are finally made on the selection of the most appropriate process parameters for FS micro-grooving of Ge substrates.

Optical constants of germanium and thermally grown germanium dioxide from 0.5 to 6.6eV via a multisample ellipsometry investigation

Thermal GeO2 oxides up to 136 nm thickness were produced by annealing Ge wafers in pure oxygen at 550 °C and 270 kPa pressure for up to 10 h. The oxidation kinetics followed the Deal–Grove law. Using multisample spectroscopic ellipsometry for a series of five thermal oxides with different thicknesses, the complex dielectric functions of Ge and GeO2 were determined from 0.5 to 6.6 eV, for thin-film metrology applications in Ge-based microelectronics and photonics. The dispersion of the GeO2 layer was modeled with a simple Tauc-Lorentz oscillator model, but a more complicated dispersion with eight parametric oscillators was required for Ge. A reasonable fit to the ellipsometric angles could be obtained by assuming that all thermal oxides can be described by the same dielectric function, regardless of thickness, but a slight improvement was achieved by allowing for a lower density oxide near the surface of the thickest films. The authors compare their results with literature data for Ge and bulk and thin-film GeO2.

Optimal process parameters for phosphorus spin-on-doping of germanium

The fabrication of homogeneously doped germanium layers characterized by total electrical activation is currently a hot topic in many fields, such as microelectronics, photovoltaics, optics and radiation detectors. Phosphorus spin-on-doping technique has been implemented on Ge wafers, by developing a protocol for the curing process and subsequent diffusion annealing for optimal doping. Parameters such as relative humidity and curing time turned out to affect the surface morphology, the degree of reticulation reached by the dopant source and the amount of dopant available for diffusion. After spike annealing in a conventional furnace, diffusion profiles and electrical properties have been measured. Ge loss from the surface during high-temperature annealing, due to diffusion into the source film, has been observed and quantified.

Pit Formation, Patterning and Flattening of Ge Surfaces in O2-Containing Water by Metal-Assisted Chemical Etching

Recently, metal-assisted chemical etching has attracted a great deal of attention because it is a simple and low-cost process for the fabrication of nanostructures on a semiconductor surface, mainly Si [1, 2]. This electroless etching is made possible by using noble metals, such as Pt and Ag, to catalyze the reduction of a chemical oxidant, such as H2O2, in the presence of HF. Namely, the reduction is accompanied by the selective oxidation around the loaded metals followed by the dissolution of oxide (SiO2) in HF solution. By controlling the etching conditions, a vast variety of nanostructures from porous structures to nanowire arrays can be fabricated in a chemical lab without the need for expensive equipment. Ge is regarded as a promising channel material in future electronics. It is necessary to develop and/or optimize wet processes, such as lithography, planarization and cleaning, for Ge. Ge oxide (GeO2) is soluble in water, unlike SiO2. Also, O2 molecules dissolved in water are oxidants. These chemical properties enable us to develop a novel process for a Ge surface using metal-assisted chemical etching in water. In this study, we immersed a Ge(100) surface loaded with Pt or Ag particles with the size of 10 nm order into O2-containing water and observed the formation of inverted pyramidal etch pits around the particles. This is caused by the catalytic effect of metals whereby O2 molecules in water are reduced, resulting in an enhanced oxidation of a Ge surface to form soluble GeO2. We confirmed that the O2 concentration in water is a key in etch rate [3, 4]. Then, we tested nanoscale patterning of a Ge surface by metal-assisted etching in O2-containing water. This was achieved by scanning a metal-coated cantilever on a Ge surface in the contact mode in an atomic force microscopy setup. We found that the Ge surface scanned by the cantilever was selectively removed, and the etched depths depended on experimental conditions such as the O2 concentration in water, the pressing force of the cantilever to the Ge surface, and the conduction type (n-type or p-type) of Ge. These findings indicate that the mechanism of inducing enhanced etching along the trajectory of the cantilever probe is a catalytic chemical effect rather than a mechanical one [4]. Finally, we used this metal-assisted chemical etching to improve the microroughness of a Ge surface. In this scheme, a thin film of noble metal (Pt) was deposited on a soft elastomer pad. This Pt surface was brought into contact with a Ge wafer surface by applying 0.01 MPa in O2-containing water. Both the pad coated with the metal and the Ge wafer were rotated independently in the same plane. Consequently, the Ge surface was flattened. The flattening mechanism is as follows. First, protrusions on the Ge surface have a higher probability of coming into contact with the metal surface than do grooves. These protrusions were selectively oxidized by the catalytic effect of the metallic film in water. After the oxidized protrusions were dissolved in water promptly, a flattened surface was created [5]. [1] X. Li et al., Appl. Phys. Lett. 77, 2572 (2000). [2] Z.P. Huang et al., Adv. Mater. 23, 285 (2011). [3] T. Kawase et al., J. Appl. Phys., 111, 126102 (2012). [4] T. Kawase et al., Nanoscale Res. Lett., 8, 151 (2013). [5] T. Kawase et al., ChemElectroChem, 2, 1656 (2015).

The Improvement of GeO2 Film Characteristics on Ge Substrates Using Ultrathin Hf Metal Deposition Followed by Annealing

Combinations of high-permittivity (high-κ) dielectrics and Germanium-channel have been expected as future high-performance and low-voltage operation metal-oxide-semiconductor (MOS) devices. To realize high-k/Ge gate stacks, it is necessary to control the interfacial properties between high-k materials and Ge substrate. GeO2 has been considered one of the candidates as an interlayer to achieve high-quality High-k/Ge interface. However, GeO2 itself has many problems to overcome, such as interfacial thermal instability (GeO volatilization), water absorbency and water solubility. To fabricate a high quality GeO2/Ge system, we have to understand electrical and physical properties of the structure in detail. Especially, to clarify the degradation mechanisms and to propose improvement methods of these issues are most important challenges. The previous our studies have shown that the GeO desorption occurs during thermal oxidation process (>450C) as well as heat treatment of GeO2/Ge structure with almost same temperature. Therefore, using such the high temperature oxidation process, the interface properties have been drastically degraded, and low temperature oxidation process such as around 400C with quite low oxidation rate would be necessary to achieve good interfacial properties of GeO2/Ge structure. Post metallization technique is one of the promising means of fabricating high quality GeO2/Ge structures even high temperature oxidation would be used. In this paper, using Hf metal, which is component of typical high-k dielectric material, the effect of PMA process onto the thermal stability, water absorbency, water solubility of thick GeO2 (6-20 nm) as well as the interface properties of GeO2/Ge structure would be presented. The initial GeO2 film has been fabricated using thermal oxidation of p-type Ge (001) wafers with the oxidation temperature of as high as 500C. For the as oxidized sample, thermal stability and interface property from C-V characteristics was quite poor, and water contents in the as oxidized GeO2 films were quite large after exposure to air for 72h. The etching rate of the GeO2 film in pure water is quite high, so after the etching for several seconds in pure water, 6nm GeO2 film on Ge substrate disappeared. Deposition of ultrathin Hf metal (1nm) on thick GeO2 film followed by the heat treatment of 300C, on the other hand, the characteristics of GeO2 itself have been drastically improved: high thermal stability, low water contents after 72h air exposure. It was also shown the electrical properties of GeO2/Ge interface have been drastically improved from the C-V measurements with the measurement frequency of 1000 to 10 KHz. The remarkable feature of the GeO2 films after ultrathin Hf metal deposition followed by the heat treatment was that the quite high durability from pure water rinse. 6nm-thick GeO2 films were still remaining even after the pure water rinse for several ten minutes. It is probably due to the change of electronic deviation between Ge-O bonds in whole GeO2 film with the contents of several percent of Hf atoms in the GeO2 film.

The Effect of H-Implantation Energy on the Annealing Kinetics of Germanium Surface Blistering

The impact of implantation energy on hydrogen-induced blistering in germanium is investigated. The results demonstrated that the kinetic plots (shown in Figure 1) were not only shifted through translation with the variation of H-implanted energy but also a break point occurred for H-implanted Ge with a low energy or low dose in the plot, which is a straight line accorfing to the Arrhenius formula. The dynamic plots of Ge blistering after a H-implanted Ge wafer were modified into a single straight-line with increasing H implantation energy similar to the fluence increasing. The characterizations of the cross-section transmission electron microscopy (XTEM) indicated that <001> H-platelets parallel to germanium surface played a main role in the subsequent exfoliation. According to the observation of optical microscopy for different H implantation fluences (shown in Figure 2) and the analysis of the critical statistic dimension (i.e. broken blisters) (shown in Figure 3), we propose a model (shown in Figure 4) that can reasonably explain the critical dimension variation with H-implantation energy even though the same dimension <001> H-platelets is viewed. Figure 1

Anisotropy of Seebeck coefficient in Si/Ge composite quantum dots

In this report, Si5Ge5 alloy and Si/Ge composite quantum dots (CQDs) layers were grown on Si substrates. Seebeck coefficient (S) of Si and Ge wafers, as well as these two samples, were patterned and measured from 60 to 180 °C in [110] and [010] directions. For Si, Ge, and Si5Ge5, the S of each is a constant in this temperature range. However, the S of the CQDs at 60–80 °C is anomalous and much higher than the others. The behavior of the voltage difference is linear to the temperature difference even as large as 50 °C, except for CQDs at 60–80 °C. This result indicates that a narrow distribution of carriers energy with a sharp change in density of state near Fermi-level and selective carrier scattering in the miniband at Si/Ge interface make the discrepancy of charge transport enhanced. The CQDs can be a good candidate for temperature sensing and thermoelectric applications due to their high S and low thermal conductivity near room temperature.

Chemical wet etching of germanium assisted with catalytic-metal-particles and electroless-metal-deposition

Ge nanostructures were fabricated by wet processes based on etching assisted with the catalytic-metal-particles and the electroless-metal-deposition under various conditions. In the etching assisted with catalytic-metal-particles, we used HF+H2O2 solutions after forming Ag particles on the Ge wafer surfaces from an AgNO3 solution. We succeeded in fabrication of porous layers on the Ge substrates and found that the pore sidewall inclination angles with respect to the surfaces can be controlled by the H2O2 concentrations. In the etching assisted with electroless-metal-deposition, we fabricated whisker-like nanostructures and demonstrated that their size and morphology can be varied by changing the AgNO3 concentration, deposition/etching time and the substrate resistivity. We have revealed differences between Ge and Si in the metal-catalyzed etching and pointed out problems in Ge nanowire fabrication via a wet chemical etching.

Evaluation of four inch diameter VGF-Ge substrates used for manufacturing multi-junction solar cell**Project supported by the National Natural Science Foundation of China (No. 61474104).

Low dislocation density Ge wafers grown by a vertical gradient freeze (VGF) method used for the fabrication of multi-junction photovoltaic cells (MJC) have been studied by a whole wafer scale measurement of the lattice parameter, X-ray rocking curves, etch pit density (EPD), impurities concentration, minority carrier lifetime and residual stress. Impurity content in the VGF-Ge wafers, including that of B, is quite low although B2O3 encapsulation is used in the growth process. An obvious difference exists across the whole wafer regarding the distribution of etch pit density, lattice parameter, full width at half maximum (FWHM) of the X-ray rocking curve and residual stress measured by Raman spectra. These are in contrast to a reference Ge substrate wafer grown by the Cz method. The influence of the VGF-Ge substrate on the performance of the MJC is analyzed and evaluated by a comparison of the statistical results of cell parameters.

Sn-based Ge/Ge0.975Sn0.025/Ge p-i-n photodetector operated with back-side illumination

We report an investigation of a GeSn-based p-i-n photodetector grown on a Ge wafer that collects light signal from the back of the wafer. Temperature dependent absorption measurements performed over a wide temperature range (300 K down to 25 K) show that (a) absorption starts at the indirect bandgap of the active GeSn layer and continues up to the direct bandgap of the Ge wafer, and (b) the peak responsivity increases rapidly at first with decreasing temperature, then increases more slowly, followed by a decrease at the lower temperatures. The maximum responsivity happens at 125 K, which can easily be achieved with the use of liquid nitrogen. The temperature dependence of the photocurrent is analyzed by taking into consideration of the temperature dependence of the electron and hole mobility in the active layer, and the analysis result is in reasonable agreement with the data in the temperature regime where the rapid increase occurs. This investigation demonstrates the feasibility of a GeSn-based photodiode that can be operated with back-side illumination for applications in image sensing systems.

Improvement of Germanium Channel Nmosfet By Using Fluorine Co-Implant Methods

1.Background/ Objectives and Goal Ge has been investigated as a high mobility (both hole and electron) channel material as a substitute for silicon channels in order to boost the device performances. In this paper, we successfully fabricated the Ge nMOSFETs by using fluorine co-implant method. The Ge nMOSFETs by using fluorine co-implant method has good performance with ION/IOFF ratio of ~8.6×103 at VDS = 1V and the subthreshold swing of 382 mV/dec. 2.Methods Fig. 1 illustrates the process steps and structure of our Ge nMOSFETs by using F co-implant methods. We use (100)-oriented p-type Ge wafer with resistivity 0.1~0.6 Ω-cm as the starting material. Firstly, a 400 nm field oxide was deposited on p-type Ge substrates after diluted HF cyclic surface clean. The source/drain regions were defined by photolithography, and subsequently the oxide was etched by BOE. Then a implantation was used to create an n+ source/drain with P and F co-implant at different dose and energy. Following by 100nm SiO2 capping layer, dopant activation with different sequence were accomplished through rapid thermal annealing (RTA) at 600 °C in N2. The split table of dose/energy and RTA sequence was shown in table 1. After defining the active region, a GeO2 (~2 nm) was formed at 520°C for 30 s in pure O2 ambient (~1030 mBar) and then an Al2O3 (5 nm) was covered. 3.ExpectedResults/Conclusion/Contribution Fig. 2 shows the I-V characteristics of co-implant n+-p Ge junction for different annealing sequence, we can observe that the reverse leakage currents of n-Ge contacts decreased. The sequence splits are the P implantation following by annealing at 1 minute and then F implantation following by annealing at 1minute / 2 minutes. It’s obvious that the F could passivate the defect through P implantation by sufficient thermal annealing in the P+F@RTA_1+2min co-implant sample with low reverse leakage current than the P+F@RTA_1+1minsample. Fig. 3 shows the ID-VGS transfer characteristic of the control sample and the P+F@RTA_1+2min co-implant sample of nMOSFETs with W/L =100 μm /10 μm. The measurement voltage were in the linear region at VDS = 0.1 V and the saturation region at VDS = 1 V. We can observe that the co-implant nMOSFET have superior ION current, low IOFF current, ION/IOFF ratio and good subthreshold swing. The ION/IOFF ratio of the co-implant nMOSFET was of ~8.6×103 at VDS = 1V and the subthreshold swing was of 382 mV/dec. The white line cutting is the gate dielectric GeO2 (~2 nm) and Al2O3(5 nm) on top of the Ge substrate. The Ge-nMOSFET and n+-p Ge junction device have been demonstrated by F co-implant methods on p-type Ge substrate. The F implantation can passivate the vacancies in Ge substrate and enhance the overall activated fraction of the dopant in Ge. The shallow junction, low off-state leakage current, and low series resistance could be achieved. Moreover, we also use the best condition to fabricate the Ge n-MOSFET, and superior IONcurrent, low IOFF current, ION/IOFF ratio, good subthreshold swing, and low RSD could be realized. The co-implant methods have great potential for leakage current improvement and shallow junction in the conventional Ge process. REFERENCES [1]M. S. Datta, G. Dewey, M. Doczy, B. Doyle, B. Jin, J. Kavalieros, R. Kotlyar,M. Metz, N. Zelick, and R. Chau, “High Mobility Si/SiGe Strained Channel MOS Transistors with HfO2/TiN Gate Stack,”IEEE International Electron DevicesMeeting,p.28, Dec. 2003 [2]T. Krishnamohan, C. Jungemann, and K. C. Saraswat, “A Novel, Very High Performance, Sub-20 nm Depletion-Mode Double-Gate (DMDG) Si/Si,Ge(l.,jSi Channel PMOSFET,” in IEDM Tech. Dig., 2003, pp. 687-690. Figure 1

Dark Current Suppression of Germanium Photodiode Using Metal-Interlayer-Semiconductor-Metal Structure with TiO2 interlayer

Germanium (Ge) photodetectors (PDs) are promising optoelectronics device for advanced Si photonics and optical interconnection due to excellent absorption property, near-infrared wavelengths, and process compatibility with Si-based complementary metal-oxide-semiconductor (CMOS). Ge metal-semiconductor-metal (MSM) PDs have many advantages over Ge PIN PDs in terms of low capacitance, high bandwidth, and process simplicity. However, Ge MSM PDs have large dark current because of a low hole barrier height induced by severe Fermi-level pinning between the metal and Ge, which results in poor sensitivity and large power consumption of PDs. In this work, the dark current of Ge MSM PD was tremendously reduced by introducing asymmetric metal-interlayer-semiconductor-metal (MISM) structure [Fig. 1]. As shown in Fig 2, a thin TiO2 layer was selected as the interlayer to reduce hole dark current by enhancing the hole Schottky barrier and the proposed structure can collect the photo current efficiently due to almost zero conduction band offset between TiO2 and Ge. Low p-type Ge wafer was used to minimize bulk defect current. To form MISM structure, TiO2 interlayer was deposited by atomic layer deposition (ALD) system at process temperature of 250 °C. To increase responsivity, finger-type PD was used with 10 um finger spacing and 10 um finger width. Metal-semiconductor (MS) contact region is defined by e-beam lithography and etched by 6:1 buffered HF, then metal-interlayer-semiconductor (MIS) contact region is defined by e-beam lithography. Cu contact was formed by e-beam evaporation and lift off process. As a result, MISM structure exhibits tremendous dark current reduction by approximately 4,000 times at a bias voltage of 1 V. The dark current reduces as the TiO2 thickness increases as shown in Fig. 3. In case of 1 nm-thick TiO2 interlayer the dark current is hardly reduced compared to symmetric MSM structure because most of holes can flow through 1 nm-thick TiO2 interlayer by tunneling. The hole dark current from the metal side diminishes as TiO2 thickness increases because hole tunneling probability decreases. The dark current with 3 nm-thick and 5 nm-thick TiO2 is reduced by 64 times and 3,970 times at 1 V, respectively, from symmetric MSM structure. As shown in Fig. 4, photo I-V measurement was carried out on asymmetric Ge MISM PD with 5 nm-thick TiO2 interlayer with collimated infrared laser (λ=1.55 um). Measured photo current value was 0.2 mA and it was saturated at 0.6 V, and the sensitivity of the PD was 24.52 at 1 V. In summary, we tremendously suppress dark current by approximately 4,000 times at 1 V using MISM structure. TiO2 interlayer of asymmetric MISM structure efficiently decrease hole dark current, and this structure can be promising structure for dark-current suppression in Ge MSM PD. Figure 1

Development of NTD-Ge Cryogenic Sensors in LUMINEU

One of the goals of LUMINEU is to develop NTD-Ge sensors for various applications. The steps are to produce NTD-Ge sensors first, then to study the dependence of their performance on the production parameters, and finally to optimize their electric contacts. In this paper, we present the different possibilities for estimating and measuring the real neutron fluence received by each Ge wafer irradiated in a thermal neutron reactor. Measurements of their resistivity at 300 K indicate a fluence discrepancy from the expected value and confirm the homogeneity of the doping throughout the volume. In addition, we present a method allowing an improved estimation of the impedance below 30 mK just by measuring the ratio of the NTDs’ resistivity at 77 and 4 K.

Medium-energy ion irradiation of Si and Ge wafers: studies of surface nanopatterning and signature of recrystallization in 100 keV Kr+ bombarded a-Si

We report new and exciting experimental results on ion-induced nanopatterning of a-Si and a-Ge surfaces. The crystalline Si (100) and Ge (100) wafers were amorphized and an a/c interface was developed by pre-irradiation with a 50 keV Ar+ beam at normal incidence with an ion fluence of 5.0 × 1015 ions cm−2. These amorphized surfaces were post-irradiated with Ar+ and Kr+ beams at an angle of 60°. The post irradiation was done with ion fluences of 1.0 × 1017 ions cm−2. For each beam, two energies (50 and 200 keV for Ar+, 100 and 250 keV for Kr+) were chosen to ensure ion stopping in both sides of the a/c interface. Regular nanopatterning (in the form of ripples) is observed on the Ge surface only with the post irradiation of the Kr+ beam. The Si surface showed regular nanopatterning with the irradiation of both beams with two energies. For the ion beams crossing the a/c interface, ripples of higher amplitude and longer wavelength were formed. Further, the irradiation with a heavy beam yielded surface ripples of relatively larger amplitudes. The Raman measurements confirm amorphization of the pre-irradiated surfaces. Surprisingly, the post-irradiated Si surface with the 100 keV Kr+ beam showed evidence of recrystallization. In the paper we discuss the physics at the interface and explain the experimental findings.

Suppression of segregation of the phosphorus δ-doping layer in germanium by incorporation of carbon

The successful formation of abrupt phosphorus (P) δ-doping profiles in germanium (Ge) is reported. When the P δ-doping layers were grown by molecular beam epitaxy (MBE) directly on Ge wafers whose surfaces had residual carbon impurities, more than a half the phosphorus atoms were confined successfully within a few nm of the initial doping position even after the growth of Ge capping layers on the top. On the other hand, the same P layers grown on Ge buffer layers that had much less carbon showed significantly broadened P concentration profiles. Current–voltage characteristics of Au/Ti/Ge capping/P δ-doping/n-Ge structures having the abrupt P δ-doping layers with carbon assistance showed excellent ohmic behaviors when P doses were higher than 1 × 1014 cm−2 and the capping layer thickness was as thin as 5 nm. Therefore, the insertion of carbon around the P doping layer is a useful way of realizing ultrashallow junctions in Ge.

Laser-induced particle size tuning and structural transformations in germanium nanoparticles prepared by stain etching and colloidal synthesis route

In this study, with the aid of Raman measurements, we have observed transformations in small (∼3 nm and ∼10 nm) free-standing Ge nanoparticles under laser light exposure. The nanoparticles were obtained by the chemical stain etching of a monocrystalline Ge wafer and of Ge powder and by colloidal synthesis route. We found that the transformation path depends on laser power and exposure time. At relatively low values of the laser power (2 mW) over a period of 100 min, the Raman signal indicates transformation of the sample from a nanocrystaline to bulk-like state, followed by partial oxidation and finally a conversion of the entire sample into alpha-quartz type GeO2. However, when the laser power is set at 60 mW, we observed a heat release during an explosive crystallization of the nanocrystalline material into bulk Ge without noticeable signs of oxidation. Together with the transmission electron microscopy measurements, these results suggest that the chemical stain etching method for the preparation of porous Ge may not be a top-down process as has been widely considered, but a bottom up one. Systematic studies of the laser exposure on Ge nanoparticles prepared by colloidal synthesis results in the fact that the explosive crystallisation is common for H-terminated and partially disordered Ge nanoparticles regardless of its particle size. We suggest possible bio-medical applications for the observed phenomena.

Correlation of optical reflectivity with numerical calculations for a two-dimensional photonic crystal designed in Ge

A two dimensional photonic crystal (2DPhC) with triangular symmetry is investigated using optical reflectivity measurements and numerical calculations. The system has been obtained by direct laser writing, using a pulsed laser (λ = 775 nm), perforating an In-doped Ge wafer. A lattice of holes with well-defined symmetry has been designed. Analyzing the spectral signature of PBGs recorded experimentaly with finite difference time domain theoretical calculations one was able to prove the relation between the geometric parameters (hole format, lattice constant) of the system and its ability to trap and guide the radiation in specific energy range. It was shown that at low frequency and telecommunication ranges of transvelsal electric modes photonic band gap occur. This structure may have potential aplications in designing photonic devices with applications in energy storage and conversion as potential alternative to Si-based technology.

Microstructural and electrical properties of Cu-germanide formed on p-type Ge wafer

We have investigated the microstructural and electrical properties of Cu-germanides formed by the deposition of Cu on Ge wafer, followed by rapid thermal annealing (RTA) process at the temperatures in the range of 300–700 °C. Regardless of RTA temperature, the Cu3Ge was the only phase formed as a result of solid-state reaction between Cu and Ge driven by RTA process. The RTA temperature dependency of specific contact resistivity of Cu3Ge was explained in terms of its structural evolution caused by RTA process. The RTA process at 400 °C led to the formation of Cu3Ge film having highly uniform surface and interface morphologies, allowing the minimum value of the specific contact resistivity. The samples annealed above 500 °C underwent the severe structural degradation of Cu3Ge, resulting in a rapid increase in the specific contact resistivity. After RTA at 700 °C, pyramidal Cu3Ge islands standing on a corner, distributed along Ge <110> direction were formed with epitaxial relationship on underlying Ge.

(Invited) Effects of Ge Substrate Annealing in H2 on Electron Mobility as well as on Junction Leakage in n-channel Ge MOSFETs

This paper discusses H2 annealing effect of Ge substrate on carrier mobility and junction leakage current in Ge MOSFETs. We found that H2 annealing of Ge wafer improved the electron mobility in Ge n-channel MOSFETs, while it degrades n+/p junction leakage current. Although we have not clarified the mechanisms causing such significant effects, we have found that the oxygen content in Ge surface region is phenomenologically related to above effects of Ge in H2 annealing.

Surface topography to reflectivity mapping in two-dimensional photonic crystals designed in germanium

Light confinement in a two dimensional photonic crystal (2D PhC) with hexagonal symmetry is studied using infra-red reflectance spectromicroscopy and numerical calculations. The structure has been realized by laser ablation, using a pulsed laser (λ=775nm), perforating an In-doped Ge wafer and creating a lattice of holes with well-defined symmetry.Correlating the spectral signature of the photonic gaps recorded experimentally with the results obtained in the finite difference time domain and finite difference frequency domain calculations, we established the relationship between the geometric parameters of the structure (lattice constants, shape of the hole) and its efficiency in trapping and guiding the radiation in a well-defined frequency range. Besides the gap in the low energy range of transversal electric modes, a second one is identified in the telecommunication range, originating in the localization of the leaky modes within the radiation continuum. The emerging picture is of a device with promising characteristics as an alternative to Si-based technology in photonic device fabrication with special emphasize in energy storage and conversion.