Polycrystalline Ge Research Articles

In situ low temperature growth of poly-crystalline germanium thin film on glass by RF magnetron sputtering

Structural and optical properties of germanium thin films deposited on silicon nitride coated glass are investigated with the aim to develop a material for the bottom cells of low cost monolithic tandem solar cells. The films were deposited by radio-frequency magnetron sputtering at various substrate temperatures ( T s )≤450 °C. X-ray diffraction spectra reveal the structural evolution from amorphous to crystalline phase with increasing T s We find that the film sputtered at 450 °C is poly-crystalline with strong (1 1 1) preferential orientation, confirmed by cross-sectional transmission electron microscopy. Optical band gaps of these films derived from Tauc plots, using absorption coefficient values derived from both reflectance/transmittance measurements and spectroscopic ellipsometry data, are in a reasonable agreement. Optical band gap values decrease from ∼0.88 to 0.68 eV over the transition from the amorphous to poly-crystalline phase. The absorption coefficient of the poly-crystalline Ge film is higher than that of bulk Ge over a wide waveband and exhibits an absorption tail. The optical properties upon substrate temperature are correlated with the structural properties of Ge films.

Role of Hydrogen Peroxide in Alkaline Slurry on the Polishing Rate of Polycrystalline Ge[sub 2]Sb[sub 2]Te[sub 5] Film in Chemical Mechanical Polishing

In chemical mechanical polishing (CMP), the polishing rate of Ge 2 Sb 2 Te 5 (GST) films increases sharply with H 2 O 2 concentration up to 0.2 wt % and then increases slightly with a further increase in H 2 O 2 concentration up to 3.0 wt %. However, the polishing rate of SiO 2 films increases very slightly with H 2 O 2 concentration up to 3 wt %. Polishing selectivity of GST films to SiO 2 films of over 100:1 can therefore be achieved by adding H 2 O 2 to the slurry. To understand the mechanism of GST CMP with H 2 O 2 , we investigated the chemical reaction behavior on the GST film surface using potentiodynamic measurement and X-ray photoelectron spectroscopy.

Heavily Boron-Doped Hydrogenated Polycrystalline Ge Thin Films Prepared by Cosputtering

Boron is an excellent dopant for forming germanium (Ge) shallow junctions because of its low diffusivity. This work investigates fabricating heavily boron-doped hydrogenated polycrystalline Ge thin films with an aim to develop a thin p + emitter of the bottom cell of a monolithic tandem solar cell. The films were deposited on glass by cosputtering in an argon and hydrogen mixture at 500°C. Rapid thermal annealing at 600°C for 60 s enhances the boron activation level from 6.24 × 10 19 to 1.21 × 10 20 atoms/cm 3 . The high activation level obtained with a low thermal budget indicates that the simple fabrication approach is promising.

Fabrication of large-grain polycrystalline Ge films using absorptive films

Fabrication of large-grain polycrystalline Ge films using absorptive films

Electronic structure of bulk ferromagnetic Ge 0.86Mn 0.14Te

The electronic structure of polycrystalline Ge 0.86Mn 0.14Te—ferromagnetic semiconductor with T C=110 K, has been studied by means of resonant photoemission spectroscopy for photon energies close to the Mn 3p→3d excitation. The contribution of Mn 3d states to the electronic structure of the system was revealed and position of the Mn ions in the crystal, characteristic of GeTe-based diluted magnetic semiconductors was proved.

Low-temperature growth of polycrystalline Ge thin film on glass by in situ deposition and ex situ solid-phase crystallization for photovoltaic applications

Poly-crystalline germanium (poly-Ge) thin films have potential for lowering the manufacturing cost of photovoltaic devices especially in tandem solar cells, but high crystalline quality would be required. This work investigates the crystallinity of sputtered Ge thin films on glass prepared by in situ growth and ex situ solid-phase crystallization (SPC). Structural properties of the films were characterized by Raman, X-ray diffraction and ultraviolet–visible reflectance measurements. The results show the transition temperature from amorphous to polycrystalline is between 255 °C and 280 °C for in situ grown poly-Ge films, whereas the transition temperature is between 400 °C and 500 °C for films produced by SPC for a 20 h annealing time. The in situ growth in situ crystallized poly-Ge films at 450 °C exhibit significantly better crystalline quality than those formed by solid-phase crystallization at 600 °C. High crystalline quality at low substrate temperature obtained in this work suggests the poly-Ge films could be promising for use in thin film solar cells on glass.

Effects of Si Layer Thickness on Solid-Phase Crystallization of Stacked Ge/Si/SiO2 Structures

The effects of amorphous-Si (a-Si) layer (thickness: 0–20 nm) insertion on low-temperature (<450 °C) solid-phase crystallization of a-Ge films (50 nm) were investigated. Upon the insertion of an ultrathin (<3 nm) a-Si layer, incubation time increased and saturated crystallinity slightly increased. On the other hand, upon the insertion of a thick (>10 nm) a-Si layer, incubation time significantly decreased and saturated crystallinity decreased. Grain sizes obtained at 425 °C were ∼200 and ∼50 nm upon the insertion of a-Si layers of 3 and 20 nm, respectively, which agrees with the results for saturated crystallinity. Moreover, upon the insertion of an intermediate-thickness (5–7 nm) a-Si layer, the nucleation rate and saturated crystallinity increased. These phenomena were explained on the basis of the Si-concentration profiles at interfaces. Thus, interface modulation is effective for realizing large-grain polycrystalline Ge.

Fabrication of large-grain polycrystalline Ge films using absorptive films

Amorphous germanium (a-Ge) films in samples with or without an absorptive film are crystallized by short-pulse XeF excimer laser crystallization (ELC). An in situ time-resolved optical reflection and transmission (TRORT) monitoring system combining a cw He-Ne probe laser, a digital oscilloscope and two photodetectors is developed to investigate the melting and resolidification dynamics of Ge films during ELC. TRORT measurements reveal that the longest melt duration is prolonged from 250 to 1000 ns by adding absorptive films in the samples. Absorptive films are shown to be effective in improving the melt duration of the molten state and the grain size of polycrystalline Ge films. The grain size with a diameter of approximately 12 μm can be fabricated in the superlateral growth regime for 90-nm-thick a-Ge films at room temperature in air by single-shot ELC.

Alternating-current white a-C:H thin-film light-emitting diodes with composition-graded carrier injection layers

The optoelectronic characteristics of hydrogenated intrinsic amorphous carbon (i-a-C:H) alternating-current white thin-film light-emitting diodes (ACW-TFLEDs) with composition-graded (CG) hydrogenated intrinsic amorphous silicon carbide (i-a-SiC:H, CG C) layers had been obviously improved with additionally incorporated CG hydrogenated intrinsic amorphous silicon germanium (i-a-SiGe:H, CG Ge) carrier injection layers. For an ACW-TFLED with CG Ge carrier injection layers, the electroluminescence (EL) threshold voltage and brightness were improved from 9 V 344 cd/m 2 of a CG C one to 7.5 V, 1000 cd/m 2 under direct-current forward bias, and from 9 V, 200 cd/m 2 of a CG C one to 7.8 V, 560 cd/m 2 under direct-current reverse bias, respectively, at an injection current density of 300 mA/cm 2 for brightness measurement. The enhancement of EL performance with CG Ge carrier injection layers was due to the increased carrier injection efficiency and reduced contact resistance resulting from the lower barrier and partially formed polycrystalline Ge layer between the Al (electrode)/Ge interface. Moreover, the EL intensity of an obtained ACW-TFLED increased with the frequency up to 20 kHz and then decreased rapidly and became very weak as the frequency was increased to about 100 kHz. This frequency-dependent EL behavior would be qualitatively explained with the mobility of charge carriers.

Properties of Ge Films Grown Through Inductively Coupled Plasma Chemical Vapor Deposition on SiO2 Substrates

In this study, we investigated the physical and electrical characteristics of Ge polycrystalline films deposited directly onto -covered substrates using inductively coupled plasma chemical vapor deposition (ICP-CVD). The pure Ge films that we deposited at a relatively low temperature of exhibited the same cubic structure, with primarily (111), (220), and (311) orientations identified from X-ray diffraction patterns, as those deposited at . The use of such a low temperature not only prevented the plasma window of the chamber from overheating but also allowed crack-free, thicker films to be deposited more easily. The ability to deposit Ge films on was closely linked to the hydrogen etching effect, as evidenced by the results obtained using X-ray photoelectron spectroscopy. Although the crystalline characteristics of the low-temperature as-deposited Ge films were somewhat poorer than those obtained at , subsequent furnace annealing and rapid thermal annealing with a capping layer improved the crystalline quality significantly. These results, taken together with studies of the surface morphologies and dopant activation of the recrystallized Ge films, suggest that ICP-CVD might be a simple, powerful and reliable approach for the fabrication of polycrystalline Ge thin film transistors.

Structural, electrical and mechanical characterization of magnetron-sputtered V–Ge–C thin films

V 2GeC MAX-phase thin films were deposited by DC magnetron sputter epitaxy in the temperature range 450–850 °C. The MAX-phase nucleates directly on (0 0 0 l)-oriented sapphire-wafer substrates without the need for a seed layer. The films contain, however, a small fraction of binary vanadium carbide (VC x ) inclusions. X-ray diffraction analysis furthermore shows that these inclusions partly consist of the ordered superstructure V 8C 7. The amount of Ge in the films decreases at higher temperatures, which can be attributed to Ge evaporation. At temperatures below 450 °C the films consist of polycrystalline Ge and an X-ray amorphous carbide phase attributed to VC x or V 2C. No MAX-phase was observed in this temperature region. The electrical and mechanical properties of the films were characterized.

Characterization of polycrystalline Ge thin films fabricated by short-pulse XeF excimer laser crystallization

XeF excimer laser-induced melting and recrystallization dynamics of amorphous germanium are investigated using time-resolved optical reflection and transmission measurements with a nanosecond time resolution, field-emission scanning electron microscopy, and micro-Raman spectroscopy. It is found that the disc-shaped grain with a diameter of approximately 0.8 µm is located in the complete melting regime with a melt phase duration of approximately 141–200 ns. The significant change of transmissivity is a key phenomenon revealing the excessive excimer laser fluence during excimer laser crystallization by in-situ optical measurements. Differences between the melting and recrystallization phenomenon for Si and Ge thin films are also discussed.

Organosoluble Silicon and Germanium Nanoclusters

ABSTRACTThe organosilicon nanoclusters (OSI) and organogermanium nanocluster (OGE) which have a few nanometer sized silicon or germanium cluster and organic groups bonded to the nanocluster surfaces show solubility in common organic solvents and good film processability by solution coating method. Using the coating films as precursors, inorganic silicon and germanium films were prepared by heat treatment in vacuo and laser annealing. The structural changes of the Si and Ge skeletons of the OSI and OGE by heat treatment and laser annealing were investigated by Raman spectroscopy. The laser-annealed films showed Raman bands assigned to the polycrystalline structure. The micropatterning of polycrystalline Ge by laser direct writing method was demonstrated. The organosoluble OGE is expected to be applicable as a germanium ink which gives polycrystalline Ge film.

Energy dependence of electron energy loss processes in Ge 2s photoemission

Deep core Ge 2s photoelectron spectra from polycrystalline Ge films induced by monochromatic synchrotron radiation, of 4, 6 and 8 keV were measured and analysed using two different methods, the partial intensity analysis and the extended Hüfner method to determine the spectral contributions from different electron energy loss processes due to bulk extrinsic, intrinsic and surface excitations. The obtained photon energy dependence of the ratio of these contributions was compared as a function of the photoelectron kinetic energy. It was found that the relative contribution of intrinsic excitations increase with the photon energy.

Influence of Ge substrate crystallinity on Co germanide formation in solid-state reactions

A strong influence of substrate crystallinity is observed for thin-film Co∕Ge reactions. For the detected phases (CoGe, Co5Ge7, and CoGe2), the formation temperatures on amorphous Ge (a-Ge) are found to be the lowest, while the highest are on single-crystalline Ge(100). Moreover, while the phase sequence on Ge(100) and polycrystalline Ge (poly-Ge) was unaltered, the formation of intermediate Co5Ge7 was not observed on a-Ge. It is likely that this is due to a promoted CoGe2 formation on a-Ge, resulting in a ∼200°C decrease in formation temperature (depending on the ramp rate). These observations suggest a strong competition among the formation of these Ge-rich phases.

Near-infrared camera in polycrystalline germanium integrated on complementary-metal-oxide semiconductor electronics

The authors demonstrate a two-dimensional array of Si-integrated photodetectors equipped with readout electronics and operating in the near infrared. The chip is realized in polycrystalline Ge on a silicon complementary metal oxide semiconductor circuitry and includes 512pixels, 64 analog to digital converters, dark current cancellation, and test/calibration facilities. They describe its design, fabrication, characterization, and operation as a near-infrared image sensor.

FABRICATION OF GERMANIUM NANOWIRES BY OBLIQUE ANGLE DEPOSITION

In this work, the effects of flux angle, substrate temperature and deposition rate on obliquely deposited germanium ( Ge ) films have been investigated. We observed that the porosity of the film increased as the flux angle became more oblique. It was also possible to obtain polycrystalline Ge films at a substrate temperature of 200°C when deposition was performed using an oblique angle of 87° as compared to normal incident deposition. Raman spectroscopy results indicated that a higher substrate temperature during deposition led to an increase in crystallinity of the film. Agglomeration of the Ge film was reduced at a lower deposition rate and it was possible to obtain isolated polycrystalline Ge nanowires when the deposition was carried out with the vapor flux inclined at 87° to the substrate normal for substrate temperatures between 250°C to 300°C and with a deposition rate of 0.2–1.5 Å/s. Subsequent rapid thermal annealing of such nanowires resulted in the formation of facetted crystallites.

Determination of band gap in polycrystalline Si/Ge thin film multilayers

The valence band (VB) photoemission supported by ultraviolet–visible–near infrared spectroscopy techniques were used to determine the band gap values of polycrystalline Si and Ge single layers as well as of Si/Ge multilayer structures. The band gap values obtained from VB photoemission measurements for these structures were found to be much larger than their corresponding bulks and to match well with those determined from standard optical absorption measurements. In each case, the VB offset values were obtained by considering the corresponding VB maximum as a reference. The increase in band gap in case of thin single layers of Si and Ge with respect to bulks were interpreted in terms of quantum confinement effect, while in case of multilayer sample, the effect of various factors such as (i) intermixing leading to the formation of SiGe alloy, (ii) roughness at the interface, (iii) particle size, and (iv) strain seem to play an important role in the observed change in band gap.

Investigation of the size effect on optical properties of polycrystalline Ge deposition by pulse laser deposition

The size effect of optical properties of the polycrystalline Ge/Si films prepared by pulse laser deposition (PLD) is investigated by photoluminescence (PL) and photocurrent (PC) spectra. The size of Ge nanocrystals is precisely controlled by the pulsed deposition time and then observed by the atomic force microscopy (AFM). The average size of Ge nanocrystals is about 2, 5 and 25 nm for 1, 2 and 3 min deposited sample, respectively. The size effect on optical properties of Ge nanocrystals has been analyzed by photoluminescence (PL) and photocurrent (PC) spectra. The PL peaks shift from 0.799 eV for 1 min to 0.762 eV for 3 mins; at the same time, the photocurrent peaks of the films sharply changes from 0.781 eV to 0.749 eV, the shifts of PL and PC are contributed to the quantum size effect of Ge nanocrystals.

Neutron irradiation effects on polycrystalline Ge1−Mn thin films grown by MBE

Abstract Polycrystalline Ge 1− x Mn x thin films were irradiated with neutrons, and their electrical and magnetic properties have been investigated. As-grown specimens have p-type carriers and electrical resistivities are in the range of 1.3 × 10 −4 –5.2 × 10 −4 ohm cm at room temperature. After the irradiation of neutrons the carrier type is not changed, but the electrical resistivities increase with the amount of neutron irradiation. In addition, some of neutron-irradiated Ge 1− x Mn x thin films transform from the semiconductor characteristics into the metallic characteristics at low temperature. The saturation magnetizations of neutron-irradiated Ge 1− x Mn x thin films decrease, but the coercive forces increase with the irradiation amounts. The XRD analysis suggests that the defects generated by the neutron-irradiation cause the change of electrical and magnetic properties of Ge 1− x Mn x thin films exposed to neutron irradiation.