Sb In Ge Research Articles

Долинно-орбитальное взаимодействие в германии, легированном донорами V группы: количественный анализ

In the framework of the envelope function approximation, the wave functions of electrons localized at shallow donors P, As, Sb in Ge are calculated taking into account the valley-orbit coupling caused by the donor short-range potential. It is proposed an approach that makes it possible to include inter-valley mixing in the equation for a multi-component envelope function. The calculation of the effects of the valley-orbit interaction was carried out according to the perturbation theory, while the "bare" single-valley functions were found using the Ritz method. The parameters of the short-range part of the potential and the coefficient of inter-valley mixing were found individually for each donor, making it possible to obtain the best agreement with the results of experimental measurements of the energies of the singlet and triplet states. The envelope functions of the 1s(A1) and 1s(T2) states are calculated. The parameters of the valley-orbit interaction are found for each donor. It is also shown how the functions of the excited 2s, 2p0, 2p±, 3p0 states should be modified in order to remain orthogonal to the singlet and triplet functions within the framework of a more rigorous multivalley model.

Diffusion properties of n-type dopants diffused from spin on glass into Ge

Solid phase diffusion properties of three typical n-type dopants (P, As, and Sb) in Ge have been studied through experimental depth profiles of dopants diffused from spin on glass (SOG) films. Numerical calculations of dopant profiles in Ge are performed to extract the diffusion constant through comparison with the experimental profiles. It is pointed out that experimental results of diffusion at low temperature are important to correctly examine the influence of negative charge states of a vacancy on dopant diffusion. It is found that vacancies with the charge states of −2 mediate the diffusion of P and As without implantation-induced defects. The diffusion constants of P and As, obtained in this study, are larger than those for intrinsic diffusion, while that of Sb is almost the same as that for intrinsic diffusion. The present larger diffusion constants of P and As can be explained by the supply of vacancies from Ge surfaces via E-centers during diffusion from SOG.

Influence of the Growth Conditions and Doping Level on the Luminescence Kinetics of Ge:Sb Layers Grown on Silicon

The emission properties of Ge layers grown on Si(001) substrates and doped with Sb to different levels are studied by means of steady-state and time-resolved photoluminescence spectroscopy. It is shown that the peak of the steady-state photoluminescence intensity of n-Ge/Si layers at room temperature is observed at an Sb concentration close to the level of the equilibrium solubility of Sb in Ge (~1019 cm–3), which is in agreement with previously obtained results. Studies of the kinetics of photoluminescence associated with direct radiative transitions in Ge show that an effect on the kinetics is produced not only by the concentration of introduced donors, but also the conditions of formation, among them the deposition temperature of n-Ge layers. It is found that an increase in the Sb concentration results in a decrease in the charge-carrier lifetime. It is established that the low growth temperatures required to attain high doping levels in Ge layers also yield a substantial decrease in the charge-carrier lifetime compared to that in Ge layers produced at high temperatures. The conditions of short-term thermal annealing of the structures are determined, wherein the above-mentioned negative effects can be compensated, i.e., the photoluminescence intensity can be enhanced and the charge-carrier lifetime can be extended.

Влияние условий роста и уровня легирования на кинетику люминесценции слоев Ge : Sb, выращенных на кремнии

Light-emitting properties of Ge-on-Si(001) layers doped by Sb were studied by stationary and time-resolved photoluminescence (PL) at room temperature. It was obtained that the PL intensity of n-Ge/Si(001) structures is maximized when the doping level is close to the equilibrium solubility of Sb in Ge (~1019 cm-3) which is in accordance with the previously published data. Time-resolved studies of the direct-related PL signal have shown that both the donor density and the growth conditions of doped layer, in particular, the growth temperature influence the PL kinetics. It was obtained that the increase of doping level leads to the decrease of the characteristic carrier lifetime. Moreover, usage of low growth temperatures which is needed to form the doped n-Ge layers also results in shortening of the carrier lifetime as compared with Ge layers grown at high temperatures. It was found that rapid thermal anneal at proper conditions could partially compensate the above mentioned detrimental effects and lead to the increase of both the PL intensity and carrier lifetime.

Comparative Analysis of the Luminescence of Ge:Sb Layers Grown on Ge(001) and Si(001) Substrates

Comparative studies of the luminescence properties of Sb-doped Ge layers grown on Ge(001) and Si(001) substrates are carried out. It is shown that, in contrast to the case of Ge:Sb layers grown on Si, a considerable contribution to the photoluminescence signal from Ge:Sb/Ge(001) layers is made by indirect optical transitions. This fact is attributed to the longer charge-carrier lifetime in Ge:Sb/Ge homoepitaxial structures because of the lack of crystal-lattice defects related to the relaxation of elastic strains in such structures. It is shown that the experimentally observed significant increase in the contribution of direct optical transitions to the total photoluminescence signal with increasing doping level of Ge:Sb/Ge(001) layers results from an increase in the population of electron states in the Γ valley. At Sb concentrations much higher than the equilibrium solubility of Sb in Ge, partial electrical activation of the impurity is observed, and in this case, a profound effect on the emission properties of Ge:Sb layers grown on different substrates is produced by nonradiative-recombination centers, whose role can be played by clusters of impurity atoms.

Influence of thermal annealing on the electrical and luminescent properties of heavily Sb-doped Ge/Si(001) layers

In this paper, we report on the formation of heavily n-doped Ge:Sb layers on Si(001) substrates by MBE with active dopant concentration exceeding 1020 cm−3 and discuss their thermal stability. Rapid thermal annealing was applied to the samples with different doping densities being both below and above the equilibrium solubility limit of Sb in Ge. Experimentally obtained changes of the impurity atomic concentration and carrier density were attributed to Sb bulk diffusion, desorption and dopant clustering. The qualitatively different modifications of room-temperature photoluminescence (PL) due to annealing were obtained for the n-Ge layers with different doping levels. In particular, for the doping levels which were below or close to the equilibrium solid solubility the overall positive impact of annealing on the PL intensity was observed. However, for the n-Ge layers with higher doping levels a more complex behavior was obtained, namely, a significant drop followed by the subsequent partial restoration of the PL intensity with the increase of annealing temperature. Changes of the PL response were attributed to the two main processes which occur during thermal treatment—annealing of the point defects generated due to low-temperature growth of a doped layer and dopant cluster formation—which have the opposite impact on the PL intensity. The obtained results allowed us to formulate the recommendations on thermal treatment of the n-type doped Ge layers, which may be useful for Ge-based Si photonics applications.

X‐ray photoelectron spectroscopy analysis of Ge–Sb–Se pulsed laser deposited thin films

AbstractPulsed laser deposition was used to prepare amorphous thin films from (GeSe2)100−x(Sb2Se3)x system (x = 0, 5, 10, 20, 30, 40, 50, and 60). From a wide variety of chalcogenide glass‐forming systems, Ge–Sb–Se one, especially in thin films form, already proved to offer a great potential for photonic devices such as chemical sensors. This system has a large glass‐forming region which gives the possibility to adjust the chemical composition of the glasses according to required physical characteristics. The chemical composition of fabricated thin films was analyzed via X‐ray photoelectron spectroscopy (XPS) and compared to energy dispersive spectroscopy (EDS) data. The results of both techniques agree well: a small deficiency in chalcogen element and an excess of antimony was found. The structure of as‐deposited thin films has been investigated by XPS. The presence of the two main structural units, [GeSe4] and [SbSe3] proposed by Raman scattering spectroscopy data analysis, was confirmed by XPS. Moreover, XPS core level spectra analysis revealed the presence of M–M bonds (M = Ge, Sb) in (Ge,Sb)–Ge–(Se)3 and (Ge,Sb)–Sb–(Se)2 entities that could correspond to Ge‐based tetrahedra and Sb‐based pyramids where one of its Se atoms at corners is substituted by Ge or Sb ones. The content of depicted M–M bonds tends to increase with introduction of antimony in the amorphous network of as‐deposited thin films from x = 0 to x = 40 and then it decreases. XPS analysis of as‐deposited thin films shows also the presence of the (Ge,Sb)–Se–(Ge,Sb) and Se–Se–(Ge,Sb) entities.

Segregation of Sb in Ge epitaxial layers and its usage for the selective doping of Ge-based structures

The segregation of Sb in Ge epitaxial layers grown by the method of molecular beam epitaxy on Ge (001) substrates is investigated. For a growth temperature range of 180–325°C, the temperature dependence is determined for the segregation ratio of Sb in Ge, which shows a sharp increase (by more than three orders of magnitude) with increasing temperature. The strong dependence of the segregation properties of Sb on the growth temperature makes it possible to adapt a method based on the controlled use of segregation developed previously for the doping of Si structures for the selective doping of Ge structures with a donor impurity. Using this method selectively doped Ge:Sb structures, in which the bulk impurity concentration varies by an order of magnitude at distances of 3–5 nm, are obtained.

Making germanium, an indirect band gap semiconductor, suitable for light-emitting devices**Invited talk at the 7th International Workshop on Advanced Materials Science and Nanotechnology IWAMSN2014, 2-6 November, 2014, Ha Long, Vietnam.

Germanium (Ge) is a group-IV indirect band gap semiconductor but the difference between its direct and indirect band gap is only 140 meV. It has been shown that when Ge is subjected to a tensile strain and a heavy n-doping level, room-temperature photoluminescence (PL) can be greatly enhanced. Among these two factors, achieving a heavy n-doping level in Ge (i.e., electron concentrations higher than 1 × 1019 cm−3) is a challenge since the solubility of most group-V elements (P, As, Sb) in Ge is very low. We report here Ge growth on silicon substrates using molecular beam epitaxial (MBE) technique. To enhance the n-doping level in Ge, a specific n-doping process based on the decomposition of the GaP compound has been implemented. The GaP decomposition allows producing P2 molecules, which have a higher sticking coefficient than that of P4 molecules. We show that phosphorus doping at low substrate temperatures followed by flash thermal annealing are essential to get a high doping level. We have obtained an activate phosphorus concentration up to 2 × 1019 cm−3 and room-temperature PL measurements reveal an intensity enhancement up to 50 times. This result opens a new route for the realization of group-IV semiconductor optoelectronic devices.

Anomalous transport of Sb in laser irradiated Ge

Excimer laser annealing is shown to be very promising to promote Sb incorporation in Ge up to concentrations as high as 1 × 1021 at./cm3. However, we demonstrate that when Ge is melted by laser irradiation, a high excess of vacancies is generated in the molten region. These vacancies induce Sb electrical deactivation at the melt depth through the formation of Sbm-Vn complexes that act as a sink for further Sb atoms, even leading Sb to back-diffuse towards the surface, against the concentration gradient. These results are fundamental for the realization of new generation Ge-based micro and optoelectronic devices.

Dopant effects on solid phase epitaxy in silicon and germanium

The kinetics of dopant-enhanced solid phase epitaxy (SPE) are studied in amorphous silicon (a-Si) and germanium (a-Ge) layers formed by ion implantation. Implanted Sb dopants into a-Ge up to a concentration of 1 × 1020 cm−3 are considered and compared to As implanted layers at similar concentrations. Although an active Sb concentration above the solubility limit is achieved, a significant portion of the implanted atoms are not. P, As, and B enhanced SPE rates in Si from the literature are also considered. The relative velocities of P and As in Si is similar to that of As and Sb in Ge. Theoretical predictions using a simple form of the generalized Fermi level shifting model, which incorporates both dopant and dopant-induced stress effects, is shown to agree well with the data. A single set of two parameters are determined, which describe the dopant enhanced SPE data well independent of dopant species and concentration.

High n-Type Antimony Dopant Activation in Germanium Using Laser Annealing for $\hbox{n}^{+}/\hbox{p}$ Junction Diode

Highly activated n-type dopant is essential for n+/p germanium diodes which will be in use for source/drain regions in Ge n-MOSFET as the geometry scaling proceeds. This letter has investigated a combination of ion implantation of Sb in Ge and subsequent laser annealing, which resulted in highly activated Sb beyond 1020 cm-3. Well-behaved Sb-doped nv/p Ge diode I-V characteristics have been demonstrated combined with TEM, SIMS, and spreading resistance profiling characterization.

Stability of Donor-Pair Defects in Si1–xGex Alloy Nanowires

We perform density-functional calculations to investigate the defect properties of group-V elements (P, As, Sb) in Si, Ge, and Si1–xGex alloy nanowires. In all nanowires, P dopants have a tendency to form donor-pair defects, which consist of two dopants at the first nearest distance, when the wire diameter decreases below a critical value. The quantum confinement and chemical bonding effects play a role in stabilizing donor-pair defects against isolated substitutional donors. As the donor-pair defect has a deep level in the band gap, which is electrically inactive, the doping efficiency is reduced in small-diameter nanowires. As the Ge concentration increases, the formation of the donor-pair defect becomes more favorable, lowering further the doping efficiency. On the other hand, with As and Sb dopants, which have the larger atomic radii, the formation of donor-pair defects is suppressed due to large strain energies. Uniaxial compressive strain also reduces the stability of donor-pair defects and thereby ...

Electrical Characteristics of Germanium $\hbox{n}^{+}/ \hbox{p}$ Junctions Obtained Using Rapid Thermal Annealing of Coimplanted P and Sb

Highly activated n-type dopant is essential for n+ /p germanium diodes which will be in use for source/drain regions in Ge n-MOSFETs as geometry scaling proceeds. Rapid thermal annealing of coimplanted P and Sb in Ge has provided n-type dopant activation beyond 1 × 1020 cm-3. However, there are limited reports on the electrical characteristics of these junctions. This letter has investigated the temperature-dependent diode I-V characteristics and contact resistance of metal-n+ Ge contacts. Well-behaved n+ /p Ge diodes (Ion/Ioff >; 105 and η <; 1.2) and significantly reduced contact resistance (ρc ~ 8 × 10-7 Ω · cm2) have been demonstrated.

High-level incorporation of antimony in germanium by laser annealing

In this work we investigate pulse laser annealing as an alternative approach to reach high-level incorporation of Sb in substitutional location in crystalline germanium. Laser irradiation is demonstrated to recover also those structural defects, like honeycomb structures, that form during high-fluence heavy-ion implantations in Ge and that cannot be eliminated by conventional thermal treatments. Indeed, concentrations of substitutional Sb higher than 1×1021 at./cm3 have been obtained, well above the solid solubility of Sb in Ge. The strain induced on the Ge host lattice is also investigated, evidencing that the obtained Sb doped Ge layer is pseudomorphic to the Ge substrate while positively strained by the substitutional Sb atoms present within the Ge matrix. The kinetics of this Sb-rich Ge alloy phase is finally investigated, showing that most of Sb goes out of lattice with increasing the annealing temperature up to 488 °C, leading to a decrease in the related lattice deformation. These results are very relevant for the future high-mobility channel technology.

Stress-enhancement of certain spectral lines of Sb in Ge

The piezospectroscopy of Sb in Ge, with a compressive force F ‖ 〈1 1 1〉, has been reinvestigated using state-of-the-art instrumentation. In the high stress limit, where the splitting of the donor states is an order of magnitude larger than the valley-orbit (chemical) splitting of the ground state, the results are remarkable, yielding for E ‖ F, a series of nine very sharp stress-induced components, five of which belong to the np 0 (1) series. It is not clear if the other four also belong to this series. For E ⊥, seven components, mainly of the np ± (1) and nf ± (1) series, are observed.

Optical Absorption Cross-Section of Sb in Ge

Optical Absorption Cross-Section of Sb in Ge

The ionisation of impurity states of Sb in Ge, connected with L‐ and X‐valleys of the conduction band

The ionisation of impurity states of Sb in Ge, connected with L‐ and X‐valleys of the conduction band

Piezoresistance ofn-Type Germanium

The change of electrical resistance in uniaxial tension has been measured over the range 6\ifmmode^\circ\else\textdegree\fi{}K to 300\ifmmode^\circ\else\textdegree\fi{}K for several single-crystal specimens of germanium doped with arsenic or antimony. The tensile stress was varied from 1\ifmmode\times\else\texttimes\fi{}${10}^{7}$ to 5\ifmmode\times\else\texttimes\fi{}${10}^{8}$ dynes/${\mathrm{cm}}^{2}$. Particularly at low temperatures where most of the carriers are bound to impurity centers, the piezoresistance of the conduction band departs strongly from linearity in stress. For the large piezoresistance effects measured with uniaxial stress in [110] direction, these departures depend in size and magnitude on the kind of donor impurity. It is shown that if the strain-induced shift of the Fermi energy is taken into consideration these effects are to be expected from the electron transfer model, which attributes the large piezoresistance to the strain-induced changes of the electron concentrations in the various conduction band valleys. Theoretical predictions concerning the lowest donor states---a one-fold $1s$-like ground state and a higher lying three-fold state---are verified for As in Ge. The energy separation between these two states is (4.10\ifmmode\pm\else\textpm\fi{}0.15)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ ev for As and at least by an order of magnitude smaller for Sb in Ge. The deformation potential constant (conduction band) for pure shear strain was found to be ${E}_{2}=19.2\ifmmode\pm\else\textpm\fi{}0.4$ ev at 6.6\ifmmode^\circ\else\textdegree\fi{}K. The mobility anisotropy of a valley was found to decrease with decreasing $T$ because of anisotropic scattering by ionized impurities.

Equalibrium Thermochemistry of Solid and Liquid Alloys of Germanium and of Silicon. II. The Retrograde Solid Solubilities of Sb in Ge, Cu in Ge and Cu in Si

Equalibrium Thermochemistry of Solid and Liquid Alloys of Germanium and of Silicon. II. The Retrograde Solid Solubilities of Sb in Ge, Cu in Ge and Cu in Si