N-type Germanium Research Articles

Characterization of Nickel Germanide Schottky Contacts for the Fabrication of Germanium p-channel MOSFETs

Nickel germanide Schottky contacts, formed by rapid thermal annealing of thin nickel films, have been characterized on n-type germanium wafers for a range of RTA temperatures. The highest Schottky barrier heights for electrons (= 0.6-0.7 eV) were obtained for RTA temperatures of approximately 300°C. For this RTA schedule, the corresponding barrier height for holes is close to zero, ideal for Schottky contacted p-channel germanium MOSFETs. When the RTA temperature was increased to 400oC, a dramatic reduction in electron barrier height (< 0.1 eV) was observed. This RTA schedule, therefore, appears ideal for ohmic source/drain contacts to n channel germanium MOSFETs. From sheet resistance measurements and XRD characterization, nickel germanide formation was found to occur at 300oC and above. The NiGe phase was dominant for RTA temperatures up to at least 435oC.

Single-Electron Transport through Semiconducting Nanowires: A Comparison between Silicon and Germanium

Single-electron transistors (SETs) have been fabricated with n-type monocrystalline silicon nanowires (SiNWs) and germanium nanowires (GeNWs) separately. Comparisons of the single-electron transport characteristics between them have been studied at low temperatures. Coulomb oscillations of both devices were found with almost equidistant peak spacing and largely varied peak heights, while charge-stability diagrams showed almost identical diamond-shaped dimensions. Noticeably, for the GeNW-SET, the spacing between neighboring Coulomb-oscillation peaks alternately changed in some gate-voltage (Vg) regions, indicating the even–odd effect. On the contrary, the SiNW-SET did not show such effect in the entire measured Vg region. The comparison indicates that the quantum effect is much more prominent in the GeNW-SET than in the SiNW-SET.

Improved germanium n+/p junction diodes formed by coimplantation of antimony and phosphorus

Obtaining heavily-doped n-type germanium (Ge) is difficult since n-type dopant activation in Ge is limited to less than 5×1019 cm−3 which is far below the solid solubility limit of phosphorus (P) in Ge. Such poor activation has limited the rectifying properties of n+/p Ge diodes. This work is aimed at understanding the challenge of forming highly rectifying n+/p diode as well as enhancing rectification of n+/p diode by using antimony (Sb) and P coimplantation process. Enhanced n+ doping of greater than 1020 cm−3 in Ge obtained by Sb/P codoping results in enhanced rectification in Ge n+/p junction diode.

A single-electron transistor and an even-odd effect in chemically synthesized Ge nanowires

Single-electron transistors have been fabricated with individual n-type monocrystalline germanium nanowires to realize an electron single-spin in a quantum dot. At low temperatures, well-pronounced Coulomb oscillations, with almost equidistant peak spacings and strongly varied peak amplitudes, were observed in a wide range of the back-gate voltage (Vg). The charge-stability diagram showed almost identical diamond-shaped dimensions and the charging energy turned out to be 110 μeV. In some Vg range, the two-electron periodicity in the addition energy was found, indicating the even-odd effect due to an alternate change of electron spin between 0 and 1/2. This work suggests the possible application to an electron-spin quantum-bit even with many electrons residing in the dot.

Analysis of Tunable Multiple-Filtering Property in a Photonic Crystal Containing Strongly Extrinsic Semiconductor

In this work, we analyze the tunable multiple-filtering property at infrared frequency in a finite semiconductor-dielectric photonic crystal (SDPC), (AB) P A, where A is a strongly extrinsic semiconductor, n-type germanium (n-Ge). B is a dielectric material, and P is the number of periods. It is found that multiple filtering phenomenon can be obtained in the region where the permittivity of n-Ge is negative. The number of resonant peaks is found to be equal to P. With the permittivity of n-Ge being concentration-dependent, these resonant peaks can be shifted as a function of impurity concentration. The analysis indicates that such an SDPC can work as a tunable multichannel filter which is of technical use for the semiconductor applications in optical communications.

A Mathematical Approach to Determine Escape Peak Efficiencies of High-Purity Germanium Cylindrical Detectors for Prompt Gamma Neutron Activation Analysis

Determining single-escape (SE), double-escape (DE), and full-energy (FE) peak efficiencies is helpful in prompt gamma-ray neutron activation analysis, in which identifying complicated gamma peaks as well as quantifying spectra is crucial. The FE peak efficiency was measured at the National Institute of Standards and Technology for a closed-end, n-type high-purity germanium (HPGe) cylindrical detector using standard point sources, whereas SE and DEpeak efficiencies and the SE-to-DEpeak ratio for the HPGe detector were calculated using compact analytical expressions.

Determination of the laterally homogeneous barrier height of palladium Schottky barrier diodes on n-Ge (1 1 1)

We have studied the experimental linear relationship between barrier heights and ideality factors for palladium (Pd) on bulk-grown (1 1 1) Sb-doped n-type germanium (Ge) metal-semiconductor structures with a doping density of about 2.5×10 15 cm −3. The Pd Schottky contacts were fabricated by vacuum resistive evaporation. The electrical analysis of the contacts was investigated by means of current–voltage ( I– V) and capacitance–voltage ( C– V) measurements at a temperature of 296 K. The effective barrier heights from I– V characteristics varied from 0.492 to 0.550 eV, the ideality factor n varied from 1.140 to 1.950, and from reverse bias capacitance–voltage ( C −2– V) characteristics the barrier height varied from 0.427 to 0.509 eV. The lateral homogenous barrier height value of 0.558 eV for the contacts was obtained from the linear relationship between experimental barrier heights and ideality factors. Furthermore the experimental barrier height distribution obtained from I– V and ( C −2− V) characteristics were fitted by Gaussian distribution function, and their mean values were found to be 0.529 and 0.463 eV, respectively.

Yttrium hole-barrier contacts for germanium semiconductor detectors

Sputtered yttrium metal forms a thin hole-barrier contact on both p- and n-type germanium semiconductor detectors. Yttrium contacts can provide a sufficiently high hole barrier to prevent measurable contact leakage current below ∼120 K. Detectors having yttrium contacts produce good gamma-ray spectroscopy data.

Fermi level depinning at the germanium Schottky interface through sulfur passivation

We demonstrate the depinning of Fermi level on both p- and n-type germanium after sulfur passivation by aqueous (NH4)2S treatment. Schottky contacts realized using metals with a wide range of work functions produce nearly ideal behavior confirming that the Fermi level is depinned. Examination of the passivated surface using x-ray photoelectron spectroscopy reveals bonding between Ge and sulfur. It is shown that good Ohmic contacts to n-type Ge and a hole barrier height (ϕBp) of 0.6 eV to p-type Ge can be achieved after this passivation treatment, with Zr Schottky contacts. This is the highest ϕBp reported so far.

Thermal annealing behaviour of platinum, nickel and titanium Schottky barrier diodes on n-Ge (1 0 0)

Platinum (Pt) and titanium (Ti) Schottky barrier diodes were fabricated on bulk grown (1 0 0) Sb-doped n-type germanium using the electron beam whereas nickel (Ni) contacts were fabricated using the resistive evaporation system. Electrical characterization of these contacts using current–voltage (I–V) measurements was performed under various annealing conditions. The variation of the electrical properties of these Schottky diodes can be attributed to combined effects of interfacial reaction and phase transformation during the annealing process. The results have also revealed that Pt Schottky contacts are of a high quality, with low reverse currents in the order of (10−5 to 10−6) A and as-deposited ideality factors as low as 1.09. Furthermore, the samples microstructural characterization was performed by scanning electron microscopy (SEM) at different annealing temperatures. From the results, it can be concluded that the onset temperature in 30 nm Ni- and Pt/n-Ge (1 0 0) systems occurs at 500–600 °C and 600–700 °C, respectively.

Challenges and Progress in Germanium-on-Insulator Materials and Device Development towards ULSI Integration

The recent progress in the fabrication of GeOI substrates and devices is reviewed. Improvements have been made in threading dislocation density, Ge-buried oxide interface passivation, device performance. The potential of various co-integration schemes (lateral and vertical) has been illustrated as alternatives to the fabrication of n-type germanium channel devices. GeOI is also shown to be a versatile platform for the monolithic integration of Si and III-V devices and tunneling field effect transistors.

Coincidence Summing Corrections in Gamma-Ray Spectrometry Using GEANT4 Code

In this paper coincidence summing corrections in gamma-ray spectrometry have been analyzed in depth. Experimental setup included a n-type germanium detector and two efficient geometries of measurement (Marinelli beaker and air filter) calibrated with multi gamma radionuclides in the energy range of 40-1500 keV. Monte Carlo simulations were carried out using the GEANT4 code in order to develop this work. Firstly an optimization of the detector dimensions was performed to obtain the full-energy peak efficiency curve. Next, the simulation of the decay schemes for involved multi gamma radionuclides were appended to the GEANT4 code including beta, alpha, EC decay, together with the subsequent relaxation process consisting of a cascade of fluorescent X-rays and Auger electrons. In order to test the simulations an comparison between an experimental and a calculated spectra of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">133</sup> Ba point source was carried out. Finally coincidence summing effects for gamma-ray emission and X-ray, Auger electron, beta and EC electron were studied in detail.

Glass-clad single-crystal germanium optical fiber

Long lengths (250 meters) of a flexible 150 microm diameter glass-clad optical fiber containing a 15 microm diameter crystalline and phase-pure germanium core was fabricated using conventional optical fiber draw techniques. X-ray diffraction and spontaneous Raman scattering measurements showed the core to be very highly crystalline germanium with no observed secondary phases. Elemental analysis confirmed a very well-defined core-clad interface with a step-profile in composition and nominally 4 weight-percent oxygen having diffused into the germanium core from the glass cladding. For this proof-of-concept fiber, polycrystalline n-type germanium of unknown dopant concentration was used. The measured infrared transparency of the starting material was poor and, as a likely outcome, the attenuation of the resultant fiber was too high to be measured. However, the larger Raman cross-section, infrared and terahertz transparency of germanium over silicon should make these fibers of significant value for fiber-based mid- to long-wave infrared and terahertz waveguides and Raman-shifted infrared light sources once high-purity, high-resistivity germanium is employed.

Measurement of natural radionuclides in phosphgypsum using an anti-cosmic gamma-ray spectrometer

Gamma-ray spectrometry measurements have been carried out to determine the activity of natural radionuclides in a phosphogypsum sample included in a specific tight container. The gamma spectrometer includes an N-type coaxial high-purity germanium (HPGe) detector equipped with an anti-cosmic system. This measurement required the determination of linear attenuation coefficients of phosphogypsum to calculate self-absorption correction between efficiency calibration conditions and measurement ones. The results are given for the three natural chains and for 40K, in term of specific activity/g of dry material, ranging from a few Bq kg −1 to a few hundreds Bq kg −1. The equilibrium within the different families and the 235U/ 238U ratio are discussed.

Enhanced thermoelectric figure of merit in nanostructured n-type silicon germanium bulk alloy

The dimensionless thermoelectric figure of merit (ZT) of the n-type silicon germanium (SiGe) bulk alloy at high temperature has remained at about one for a few decades. Here we report that by using a nanostructure approach, a peak ZT of about 1.3 at 900 °C in an n-type nanostructured SiGe bulk alloy has been achieved. The enhancement of ZT comes mainly from a significant reduction in the thermal conductivity caused by the enhanced phonon scattering off the increased density of nanograin boundaries. The enhanced ZT will make such materials attractive in many applications such as solar, thermal, and waste heat conversion into electricity.

Electrical characterization of defects introduced during metallization processes in n-type germanium

We have studied the defects introduced in n-type Ge during electron beam deposition (EBD) and sputter deposition (SD) by deep-level transient spectroscopy (DLTS) and evaluated their influence on the rectification quality of Schottky contacts by current–voltage ( I–V) measurements. I–V measurements demonstrated that the quality of sputter-deposited diodes are poorer than those of diodes formed by EBD. The highest quality Schottky diodes were formed by resistive evaporation that introduced no defects in Ge. In the case of EBD of metals the main defect introduced during metallization was the V–Sb complex, also introduced during by electron irradiation. The concentrations of the EBD-induced defects depend on the metal used: metals that required a higher electron beam intensity to evaporate, e.g. Ru, resulted in larger defect concentrations than metals requiring lower electron beam intensity, e.g. Au. All the EBD-induced defects can be removed by annealing at temperatures above 325 °C. Sputter deposition introduces several electrically active defects near the surface of Ge. All these defects have also been observed after high-energy electron irradiation. However, the V–Sb centre introduced by EBD was not observed after sputter deposition. Annealing at 250 °C in Ar removed all the defects introduced during sputter deposition.

An accurate analytical approximation to the capacitance transient amplitude in deep level transient spectroscopy for fitting carrier capture data

An accurate analytical approximation to the capacitance transient amplitude measured by deep level transient spectroscopy as a function of the filling pulse duration is derived. The equation includes the influence of a defect concentration profile and the nonexponential trapping in the Debye tail of the depletion region. Because this equation gives an accurate approximation for all filling pulse lengths it is possible to use it for the fitting of experimental data in capture cross-section measurements. The method is implemented in a fitting routine and is demonstrated for the E1-level in Fe-implanted n-type germanium.

Study of metal-related deep-level defects in germanide Schottky barriers on n-type germanium

Deep levels have been studied in n-type germanium subjected to Co, Fe, Cu, Cr, and Pt germanidation in the temperature range between 300 and 700°C by deep-level transient spectroscopy (DLTS). It is shown that most DLTS peaks can be assigned to acceptor levels of substitutional metal atoms. However, while in the case of Co, Fe, and Cu we have clear evidence of the indiffusion of the respective metals during the germanidation step, contamination with fast-diffusing Cu dominates the spectra for the Cr and Pt samples. At the same time, the occurrence of minority carrier traps during a bias pulse in forward operation is demonstrated and the interpretation of the corresponding peaks is discussed.

Anomalous charge trapping dynamics in cerium oxide grown on germanium substrate

We have observed charge trapping phenomena in thin films of cerium oxide on n-type germanium (Ge) substrate under constant voltage stress (CVS) condition. The measured shift of the flatband voltage of a high frequency C-V curve immediately after each CVS cycle, was utilized as a method to study the capture dynamics of both preexisting and stress induced oxide defects. At low stress electric field, it is the creation of new interface traps that dominates the trapping characteristics of the corresponding metal-oxide semiconductor capacitors. At higher stress electric field, negative charges are trapped on preexisting traps uniformly located in the bulk of the oxide. From data analysis, the capture cross section of the traps is estimated to be around 1×10−19cm2 which indicates neutral traps possibly related to H+ species and/or oxygen vacancies.

RBS investigation of annealed thin gold layers on crystalline germanium

In this work we report firstly on the behaviour of Schottky barrier diodes (SBD's) when subjected to thermal treatment after metallization. To better understand this, a systematic study of the interaction between thin gold films and crystalline germanium substrates was undertaken. Gold metal films having thicknesses of 30 and 100 nm have been prepared by means of thermal evaporation on bulk-grown (111) n-type germanium doped with Sb to a level of 2.5×1015 cm-3. Before metallization the samples were first degreased and then etched in a mixture of H2O2:H2O (1:5) for one minute. Subsequently the samples have been thermally treated in Ar-atmosphere for 10 minutes and at temperatures ranging from 300 to 600°C. Rutherford backscattering spectrometry (RBS) has been performed to estimate the composition of the as-deposited and thermally treated films. It was found, that the composition of the as-deposited film remains unchanged under thermal treatment up to 340°C. Between 340°C and 360°C a gold-rich layer containing a very small amount of germanium is formed. At 361°C this layer suddenly converts to a germanium-rich layer with a small amount of gold. This transition is accompanied by the formation of agglomerates on the surface of the substrate.