Growth Of Germanium Films Research Articles

Electrodeposition of crystalline germanium thin films by the electrochemical liquid-liquid-solid method

The direct electrodeposition of crystalline germanium thin films in aqueous solutions at low temperatures represents a promising and cost-effective method for synthesising semiconductor materials. This study investigates the influence of the deposition potential and time on the characteristics of crystalline germanium thin films derived from germanium oxide precursors in aqueous solution through electrochemical liquid–liquid-solid (ec-LLS) process at low temperature. Additionally, it establishes a Ge/Cu Schottky junction by heterogeneous growth of germanium films on copper (Cu) metal via electrochemical liquid–liquid-solid–solid (ec-LLSS) process.X-ray diffraction (XRD) analysis revealed that an increase in the deposition potential to −1.7 V resulted in a shift in the crystal orientation of the germanium film from (220) to (111), while excessive deposition potential (>−2.0 V) led to a reduction in the crystallinity of the deposited samples. At a deposition temperature of 70 °C and a deposition potential of −1.8 V, the crystal cluster size and the crystal quality increased with the increasing deposition time. However, at −2.0 V, the crystallinity of the germanium film reached an optimal state after 30 min and then gradually declined with time.Charactersation techniques such as EDS, XPS and Raman spectroscopy indicated that the use of liquid electrode Ga(l) as a doping source during the electrodeposition process allowed for heterogeneous growth of Ga-doped p-type germanium films on a Cu substrate.The I-V characteristic curves demonstrated that the Ge/Cu Schottky junctions exhibited significant rectification characteristics, rendering them suitable for potential applications in solar cells.

Disilane chemisorption on SixGe1−x(100)-(2×1): Molecular mechanisms and implications for film growth rates

At low temperatures, hydrogen desorption is known to be the rate-limiting process in silicon germanium film growth via chemical vapor deposition. Since surface germanium lowers the hydrogen desorption barrier, Si(x)Ge((1-x)) film growth rate increases with the surface germanium fraction. At high temperatures, however, the molecular mechanisms determining the epitaxial growth rate are not well established despite much experimental work. We investigate these mechanisms in the context of disilane adsorption because disilane is an important precursor used in film growth. In particular, we want to understand the molecular steps that lead, in the high temperature regime, to a decrease in growth rate as the surface germanium increases. In addition, there is a need to consider the issue of whether disilane adsorbs via silicon-silicon bond dissociation or via silicon-hydrogen bond dissociation. It is usually assumed that disilane adsorption occurs via silicon-silicon bond dissociation, but in recent work we provided theoretical evidence that silicon-hydrogen bond dissociation is more important. In order to address these issues, we calculate the chemisorption barriers for disilane on silicon germanium using first-principles density functional theory methods. We use the calculated barriers to estimate film growth rates that are then critically compared to the experimental data. This enables us to establish a connection between the dependence of the film growth rate on the surface germanium content and the kinetics of the initial adsorption step. We show that the generally accepted mechanism where disilane chemisorbs via silicon-silicon bond dissociation is not consistent with the data for film growth kinetics. Silicon-hydrogen bond dissociation paths have to be included in order to give good agreement with the experimental data for high temperature film growth rate.

Molecular-dynamics simulation of germanium film growth by cluster deposition

Ge films have been grown by depositing Ge-atom clusters with different initial energies on Si(0 0 1) substrates with molecular-dynamics simulations utilizing the Stillinger–Weber (SW) many-body potentials for Ge and Si. The structural properties and the stress distribution of the films have been characterized. We find that the films formed by depositing the clusters with higher initial energies have better qualities and the stress values in such films are a little higher. We have also compared the stress value with the experimental data. In addition, we find that the stress distribution is more gradual throughout the system in the case of higher cluster energy.

Desorption of Arsenic Species during the Surfactant Enhanced Growth of Ge on Si(100)

The desorption and scattering of As4 and As2 species from the surface during the growth of germanium films on Si(100) with continuous As4 deposition is monitored using laser ionization time-of-flight mass spectrometry. A significant increase in the flux of As2 from the surface is observed when the Ge flux is admitted to the surface. Upon discontinuation of the germanium growth process, the As4 and As2 signal levels remain at this increased level. A comprehensive study of the desorption fluxes of As4, As2, and As species from both Ge(100) and Si(100) substrates was performed as a function of substrate temperature and incident As4 flux to determine the kinetics of desorption of the different species from the substrates. The behavior of the As2 desorbed fluxes as a function of surface temperature is qualitatively different on the Ge(100) and Si(100) substrates. The results indicate that the catalytic cracking of As4 to As2 is more effective on Ge(100) compared to Si(100) at substrate temperatures between 800...

Defect controlled diffusion in the epitaxial growth of germanium on Si(1 0 0)

The growth of germanium films on Si(100) substrates prepared by two different methods is studied using atomic force microscopy and reflection high energy electron diffraction. The first method uses a brief Ar+ sputter followed by annealing to desorb the remaining oxide, resulting in a flat substrate. The second method involves the pre-treatment of the sample with an oxygen plasma discharge before annealing. Pre-treating the Si(100) surface with an oxygen plasma discharge can sometimes result in etch pits that dramatically affect the growth of the germanium film. The diffusion length of germanium on the pre-treated sample at 750K is estimated to be ≥700±100nm by measuring the size of island-free terraces surrounded by etch pits.

Growth of germanium films on Si(001) substrates.

We have studied the growth of Ge layers on the Si(001) surface using molecular-dynamics techniques. In order to relieve the strain resulting from the lattice mismatch between Ge and Si atoms, Ge deposited on the Si(001) surface tends to form islands. This tendency to form three-dimensional structures was studied by monitoring the chemical potential of relaxed Ge films on top of the Si(001) surface. We find that layer-by-layer growth is favored for the first three layers of Ge deposited. To study the diffusion of Ge adatoms on ${\mathrm{Ge}}_{\mathit{n}}$Si(001) films, we have mapped out the potential-energy surfaces on such films with (2\ifmmode\times\else\texttimes\fi{}1) and (2\ifmmode\times\else\texttimes\fi{}N) reconstructions. For surfaces subject to (2\ifmmode\times\else\texttimes\fi{}1) reconstructions, the motion is anisotropic, with the fast-diffusion direction being along the dimer rows. In the case of a surface with (2\ifmmode\times\else\texttimes\fi{}N) reconstructions, fast diffusion is still along the dimer rows. However, we find additional potential-energy barriers where the missing dimers are located, which effectively confines the motion of adatoms. Finally, we have studied the initial stages of island formation by directly simulating the epitaxial growth of Ge layers on the Si(001) surface.

Real-time monitoring of a surface reaction in germanium film growth

Epitaxial germanium film growth by a surface reaction was investigated using a pulsed molecular jet. Time-resolved reflectometry was utilized for in situ monitoring of both the formation and the evolution of a chemisorbed layer of digermane. The rate of chemisorption was independent of temperature. Evolution of the adsorption layers occurred by a temperature dependent first order process, believed to be molecular hydrogen desorption. Digital growth of germanium films was demonstrated by periodically refilling the active surface sites liberated by molecular hydrogen desorption between two successive gas pulses. Epitaxial germanium films over 150 nm thick were grown on Si (100) substrates.

Microstructure modifications during early stages of ion-beam-assisted film growth of germanium on SiO 2

The early stages of ion-beam-assisted growth of germanium films on SiO 2 in ultrahigh vacuum is described. Island evolution in the early stages of film growth was studied using post-growth transmission electron microscopy. This study showed that, with increasing energy, in the ion energy range 150–350 eV, the germanium island size distribution became more uniform, the mean island size decreased while the island density increased. In addition, for a fixed ion energy, an increased ion-to atom flux ratio resulted in similar changes in microstructure distribution as were observed with increasing ion energy. A new model is qualitatively developed to explain the observed phenomenon in terms of ion-bombardment-induced adatom desorption from supercritical-sized clusters.

Growth and Etching of Germanium Films by Chemical Vapor Deposition in a GeCl4 ‐ H 2 Gas System

The etching and growth of germanium films are investigated using a gas system in the temperature range of 490°–565°C. At relatively low partial pressures less than , epitaxial growth of Ge is observed on Ge (100) surfaces, whereas at partial pressures higher than , etching of the Ge film is found to occur. In the experiments utilizing patterned substrates, where the surface consists of defined areas of Ge and , Ge is found to deposit selectively only on the exposed Ge regions. The growth reactions of Ge epitaxial films proceed through the Langmuir‐Hinshelwood mechanism: the surface reaction takes place between two hydrogen atoms dissociatively adsorbed and a surface‐adsorbed molecule. molecules adsorbed on the surface are formed directly from molecules, not through gas‐phase reduction by hydrogen. On the other hand, the etching reaction of Ge films is proved to be a reverse disproportionation reaction: . Based on the analyses of growth and etching reactions, the equation of the Ge epitaxial film's growth rate is derived as a function of partial pressure, hydrogen partial pressure, and growth temperature.

Epitaxial Films of Germanium by MOCVD

ABSTRACTA simple and easily expandable atmospheric pressure MOCVD (metal organic chemical vapor deposition) reactor for the growth of germanium films is proposed and implemented. It employs a resistively heated horizontal quartz reaction chamber. The organometallic compound tetramethylgermanium (TMGe) is used as the germanium source, and hydrogen as the carrier gas. Using this reactor, epitaxial films of germanium on <111> germanium substrates were grown at 550-650°C. The growth rate was found to increase with temperature. The single crystallinity of these films was evaluated by x-ray rocking curves, and the interface strain between the film and substrate was found to be less than 1%. These Ge/Ge samples have the same morphology as the bare substrate and their sheet resistance is 30% higher than the bare substrate value.

Activation energy and spectroscopy of the growth of germanium films by ultraviolet laser-assisted chemical vapor deposition

Emission and absorption spectroscopic studies of a reactor used to grow germanium thin films by photodissociating GeH4 at 248 nm with an excimer laser are described here. For every Ge or GeH (A→X) transition examined, the dependence of the emission line intensity on pump laser fluence was found to be quadratic, indicating that Ge and GeH have a common precursor which is itself produced by the simultaneous absorption of two 5-eV photons. This conclusion is supported by the known photochemistry of SiH4 and CH4 in the ultraviolet and the laser wavelength and intensity thresholds for the growth of Ge films. The short (∼2 μs) lifetime of GeH2 in the reactor suggests that the immediate precursor to Ge and GeH is the germyl radical, GeH3. The activation energy for Ge film growth in the temperature range 300≤T≤500 K has been measured to be 2.0±0.5 kcal/mole which suggests that the limiting mechanisms for the film growth rate are a gas-phase reaction and surface desorption of residual gases rather than surface diffusion. Radiation trapping on several Ge emission lines and absorption measurements at 422.6 nm indicate that the steady-state Ge number density in the reactor is ∼1012 cm−3 which is sufficient to account for the observed film growth rates. Spatial profiles of the atomic Ge and GeH emission from the reactor have been measured with a resolution of ∼100 μm.

The epitaxial growth of germanium films onto NaCl/mica substrates

We investigated the epitaxial growth of germanium films by evaporation in ultrahigh vacuum onto substrates consisting of an NaCl (111) film previously evaporated onto air-cleaved mica and the influence of the prior heat treatment of the mica. It was found that germanium grows partially in a parallel orientation to the substrate. The degree of orientation depends on the substrate temperature during film growth and the mica pretreatment. Water liberated from the mica seems to favour the epitaxial growth of the germanium on the NaCl (111) surface, up to an optimum substrate temperature. Beyond this temperature is causes the agglomeration of the NaCl and a decrease in the degree of orientation. Heat pretreatment of the mica, which reduces the amount of water, increases the optimum substrate temperature and hence the degree of orientation. Thick self-supporting single- crystal germanium films can be obtained with an extended mica pretreatment at 500°C and a substrate temperature of 500°C.

Heteroepitaxy of germanium thin films on silicon by ion sputtering

The successive stages of germanium film growth on the vicinal face of silicon near (111) have been studied in the range of effective thickness d f from ∼ 10 Å to 25000 Å. It was shown that the growth of the trapezoidal islands of germanium began from the steps on the silicon substrate. After coalescence of big islands, from d f > 1000 Å, the vicinal germanium surface formed, which is parallel to the initial silicon surface. The films with d f = 25000 A ̊ had hole conductivity; the carrier concentration was from 10 16 to 10 17 cm -3; mobility was from 600 to 1000 cm 2/V sec at 300 °K and from 2000 to 6000 cm 2/V sec at 77 °K.

Growth of germanium films on glass: R. K. Arora. Int. J. Electron.34, No. 2 (1973), p. 193

Growth of germanium films on glass: R. K. Arora. Int. J. Electron.34, No. 2 (1973), p. 193

Growth of germanium films on glass†

Abstract Crystalline germanium films were grown by vacuum evaporation on heated corning glass substrates. Intrinsic germanium (99-999% and of 30 Ω-cm resistivity) was evaporated from a resistance-heated tungsten conical basket pasted with a paste of sodium silicate and alumina on to cleaned microscope glass slides with the help of a conventional vacuum system at pressure between 10−5 and 10−4 torr. The electrical conductivity of the films was measured in vacuum at temperatures varying between 77°K and 400°K. The island radius of the film is calculated using the Frenkel model and the grain size was found to increase with thickness.