Thermal Donors In Silicon Research Articles

Magnesium‐Related Donors in Silicon: State of the Art

The research interest in deep donors in silicon is due in particular to the quantum structure of such centers; these are promising for application in silicon photonics in the mid‐IR range and quantum technologies. At interstitial lattice positions, magnesium atoms create double‐charge deep donors. The review is an attempt to summarize the accumulated knowledge on properties of magnesium impurity in silicon. Among methods to obtain magnesium‐doped silicon, there is focus on the impurity diffusion from the solid phase using the so‐called sandwich method. Techniques to investigate samples include Hall effect measurements, optical absorption, luminescence spectroscopy, and others. The diffusivity of magnesium in silicon and stability of parameters of doped samples under heat treatment is discussed. The energy spectrum of the helium‐like magnesium donor is considered in detail. Due to the interaction with other impurities, magnesium forms a variety of donor levels in silicon. These include complexes of Mg with substitutional acceptor atoms B, Al, Ga, In, interstitial Li, and oxygen, as well as numerous donors with a currently unknown nature. Some defects are similar to so‐called thermal donors in silicon. The pairing of Mg atoms is proved in samples prepared from the isotope 28Si‐enriched silicon.

Formation of thermal donor enhanced by oxygen precipitation in silicon crystal

The formation of thermal donors in silicon is investigated using Czochralski silicon crystals grown with different grown-in defect regions, such as voids and nuclei of oxidation-induced stacking faults. It was found that the formation rate of thermal donors during annealing at 450 °C increases with an increase in the density of oxide precipitates in the regions containing different grown-in defects. The thermodynamic model for the formation of thermal donors shows that the electrically inactive oxygen trimers as nuclei of thermal donors in an as-grown crystal increase with an increase in the density of oxide precipitates, suggesting that the formation of the nuclei is enhanced due to silicon self-interstitials emitted by oxygen precipitations during the crystal growth.

Kinetics of Generation of Thermal Donors in Silicon of Stabilization of States of Fast-Diffusing Impurities

The paper reports that the intensity of generation and the concentration of low-temperature thermal donors (LTD) at 450°C in silicon, where fast diffusing impurities (FDI) are stabilized by means of binding them into electrically neutral chemically bound complexes with sulfur, are significantly lower compared to their intensity and concentration in reference samples of silicon doped with sulfur and pure reference samples. The “Kaiser model” states that the initial rate of generation of low-temperature thermal donors is proportional to biquadrate, and their maximum concentration is to the third degree of oxygen concentration. According to the Kaiser model of thermal donor generation, LTD represent predominantly stable tetrahedrons (i.e. SiO₄ molecules). However, the Kaiser model does not take into account the possibility of interaction of oxygen with other impurities that might lead to the formation of electrically active centers. Based on the analysis of experimental results of Si<S> samples subjected to heat treatment the authors recommend a revision of the principles of LTD in silicon in view of behavior of FDI, as they play a key role in the process of the formation of LTD. Thus, in the present paper the authors effectively are attempting to shed light on the anticipated role of impurity centers with deep levels in the process of formation of thermal donors.

Tin-based donors in SiSn alloys

Tin-containing Group IV alloys show great promise for a number of next-generation CMOS-compatible devices. Not least of those are optoelectronic devices such as lasers and light-emitting diodes. To obtain reliable operation, a high control over the doping in such materials is needed at all stages of device processing. In this paper, we report tin-based donors in silicon, which appear after heat treatment of a silicon-tin alloy at temperatures between 650°C and 900°C. Two stages of the donor are observed, called SD I and SD II, which are formed subsequently. A broad long-lifetime infrared photoluminescence is also observed during the first stages of donor formation. We discuss evolving tin clusters as the origin of both the observed donors and the photoluminescence, in analogy to the oxygen-based thermal donors in silicon and germanium.

4a-YG-8 Siのサーマルドナーの消滅と欠陥の形成

4a-YG-8 Siのサーマルドナーの消滅と欠陥の形成

A Fast and Easily Implemented Method for Interstitial Oxygen Concentration Mapping Through the Activation of Thermal Donors in Silicon.

Abstract In this paper a method is presented to accurately and readily measure the interstitial oxygen concentration in silicon. This method relies on the modification of the Si resistivity after the generation of some oxygen-based Thermal Donors. The method is made very accurate due to the strong dependence of the thermal donors formation rate on the interstitial oxygen concentration. The presented procedure is non destructive and only requires a resistivity measurement setup and a standard 450 °C air furnace. Very high spatial resolution mappings can be achieved using up-to-date resistivity measurement tools.

Two-side surface photovoltage studies for implanted iron diffusion in silicon during rapid thermal anneal

Two-side surface photovoltage (TS-SPV) based on measuring SPV from both wafer sides is proposed as the approach for silicon iron contamination monitoring. TS-SPV is applied to follow diffusion of implanted iron in a lightly doped p-type silicon during rapid thermal anneal (RTA). Good correlation is found between the iron distribution versus RTA conditions in the range of 375–1100°C. The impact of thermal donors in silicon after RTA at below 700°C is illustrated. The portion of iron detectable by SPV (FeB pairs) is found as a function of RTA time and temperature. Iron diffusion activation energy was evaluated for the interstitial ionized iron Fei+ and for the interstitial neutral iron Fei0. Low thermal budget RTA combined with TS-SPV has been proven to be an effective iron contamination monitor to identify contamination sources, character, and location.

Electrical properties of thermal donors formed in silicon under elastic tensile stress

The electrical properties of thermal donors formed in the bulk and near-surface regions in silicon samples with (3–9) × 1017 cm−3 oxygen concentrations under elastic tensile stress σ of about 1 GPa have been studied. The original method allowing us to control an introduced elastic tensile stress during the thermal donor’s formation at T = 450°C by a double-crystal X-ray diffractometer has been used. The formation of thermal donors in silicon with a high oxygen concentration of 9.3 × 1017 cm−3 under tensile stress has been found to be less effective than in silicon with a low oxygen concentration of (3–5) × 1017 cm−3. Single-charged donors are formed in silicon with a low oxygen concentration under tensile stress while double-charged donors are formed in silicon with a high oxygen concentration.

What Do We Know about Hydrogen-Induced Thermal Donors in Silicon?

The hydrogen-plasma-accelerated formation of shallow thermal donors in silicon has been studied for a wide range of doping concentration and interstitial oxygen content by electrical and spectroscopic techniques. The plasma-hydrogenated material has been heat treated for different times in the temperature range of . It is shown that, besides oxygen thermal donors (OTDs), hydrogen-related shallow thermal donors (STDHs) also play a crucial role in the hydrogen-assisted creation of excess carriers. The impact of different factors on the introduction rate of the shallow donors will be discussed, whereby a strong role is played by the doping concentration and type (i.e., the Fermi-level position during the thermal anneal in air). Generally, shallow donor formation is faster in p- compared to n-type Si, which is associated with the different charge state of H. From combined deep-level transient spectroscopy and Fourier transform infrared absorption spectroscopy, it is concluded that the additional free carriers are contributed by both STDH and OTD centers, so that H not only plays a catalytic role but actively takes part in the donor formation, depending on the experimental conditions. Finally, from our data some conclusions can be made regarding the nature of the STDHs, which is still a matter of debate.

Influence of radiation defects on formation of thermal donors in silicon irradiated with high-energy helium ions

Isothermal annealing at temperatures from 370 to 410 °C was used for investigation of radiation enhanced formation of thermal donors in oxygen-rich FZ silicon irradiated with 7 MeV helium ions. Results show that formation of these defects is caused by hydrogen atoms which are diffusing from the anode contact. Hydrogen enhances diffusivity of interstitial oxygen and allows it to react with radiation defects containing vacancies and oxygen to form a new type of thermal donors. Their distribution is then given by concentration profile of radiation damage and diffusion length of hydrogen atoms. This effect occurs only in oxygen-rich silicon annealed in air and is absent in oxygen–lean silicon and samples annealed in vacuum.

What do We Know About Hydrogen-Induced Thermal Donors?

The hydrogen-plasma-accelerated formation of shallow thermal donors in silicon has been studied for a wide range of doping density and interstitial oxygen content [Oi] by electrical and spectroscopic techniques. The plasma-hydrogenated material has been heat treated for different times in the temperature range of 275 to 500 oC. It is shown that besides Oxygen Thermal Donors (OTDs) also hydrogen related Shallow Thermal Donors (STDHs) play a crucial role in the hydrogen-assisted creation of excess carriers. The impact of different factors on the introduction rate of the shallow donors will be discussed, whereby a strong role is played by the doping density and type, i.e., the Fermi level position during the thermal anneal in air. Generally, shallow donor formation is faster in p- compared with n-type Si, which is associated with the different charge state of H. From combined Deep Level Transient Spectroscopy (DLTS) and Fourier Transform Infrared (FTIR) absorption spectroscopy it is concluded that the additional free carriers are contributed by both STDH and OTD centers, so that H not only plays a catalytic role but actively takes part in the donor formation, depending on the experimental conditions. Finally, from our data some conclusions can be made regarding the nature of the STDHs, which is still a matter of debate.

Evolution of Thermal Donors in Silicon Enhanced by Self-Interstitials

The time dependence of thermal donor (TD) concentration, N(t), during annealing at 450oC was measured in samples cut from a single slab of silicon containing bands of grown-in microdefects of different types. An enormous impact of the microdefect type on the kinetic curve was observed. Samples from the interstitial region showed simple linear rise in N(t). The samples from an inner part of the vacancy region showed a complicated oscillating variation with an abrupt disappearance of the TDs at some moment followed by an immediate restoration of a linear rise. In samples from the marginal H-band of the vacancy region, an initial anneal does not produce TDs. However if this anneal was followed by a quench, subsequent anneals produce a linear rise in N(t). On the other hand, if the sample was slowly cooled, the subsequent production of TDs remained almost negligible. These observed peculiarities are accounted for by enhanced TD growth in the presence of self-interstitials (I) - due to IO species serving as vehicles for oxygen transport.

Features of the formation of thermal donors in silicon under elastic tensile stress

The formation process of electrically active oxygen-containing complexes (thermal donors) in silicon is investigated at the initial stage of thermal treatment at T < 500°C under elastic tensile stress σ = 1 GPa. It is shown that, under these conditions, the formation of singly charged donor centers is observed in silicon when the oxygen concentration is (3–5) × 1017 cm−3. When the oxygen concentration is 9 × 1017 cm−3, doubly charged donor centers form. The depth profile of thermal donors is found in the samples studied.

High-resolution magnetic-resonance spectroscopy of thermal donors in silicon

Oxygen-related thermal donors in silicon form a group of defects with very similar properties. In a magnetic resonance experiment carried out under the normally applied conditions the individual species, up to 16 have been reported, are not distinguished. Due to lack of resolution only an overall integrated signal covering the whole group is recorded. In this paper two independent ways of improving the resolution in magnetic resonance are reported and applied to the Si-NL8 spectrum of the thermal double donors and to the structurally related Si-NL10 center. Line widths of the resonances caused by unresolved hyperfine interactions with the magnetic nuclei of isotope 29Si, nuclear spin I = 1 / 2 and natural abundance 4.7%, are near 0.3 mT. Monoisotopic silicon with the 29Si concentration reduced to 0.09% has been used to observe the Si:P, Si-NL8 and Si-NL10 resonances. In this material a line width as low as 0.045 mT has been observed. The second improvement of resolution is achieved using high-frequency high-field EPR spectrometers at 92 GHz and at 140 GHz for the Si-NL8 spectrum and at 349 GHz for Si-NL10. At these higher frequencies an increase of line structure is achieved by, e.g., a factor 15 when comparing a D band (140 GHz) with a classical X band (9 GHz) experiment. Due to ‘ g strain’ an increase of line width may occur. Under the high-resolution conditions individual species of thermal donors are separated.

Small angle light scattering and clusters of thermal donors in Si

This paper reports the application of small angle light scattering technique for characterization of Si samples with clusters of thermal donors. The observed dependencies of the intensity of scattered light on the period of thermal treatment of studied samples are interpreted by a model involving the multiple light scattering events. The study shows the effect of increased oxygen concentration at places where relatively small clusters of thermal donors are formed. This offers an explanation for the “small diffusion coefficient of oxygen” paradox arising during modeling of the formation kinetics of thermal donors in silicon.

Study of the defects in oxygen implanted silicon subjected to neutron irradiation and high pressure annealing

This paper reports on capacitance measurements on Czochralski-grown and float-zone silicon subjected to oxygen implantation, subsequent neutron irradiation and finally high pressure thermal anneals. The purpose of this work was the study of the effect of irradiation on the formation of thermal donors in silicon. The observed changes in the C-V characteristic curves and profiles are discussed. We found that oxygen-ion implantation followed by neutron irradiation results in shallow and deep level acceptor-like defects formation. Prolonged heat treatment leads to thermal donor generation as usual in Cz-Si annealed at 450 °C. The most striking result of the study is finding that high pressure thermal anneals result in extra donor formation. The effects mentioned above may lead to changes in the type of conductivity depending on oxygen content in the material, hydrostatic pressure and an extent of damage caused by the irradiation.

Thermal Donors in Silicon Implanted with Rare Earth Impurities

Thermal Donors in Silicon Implanted with Rare Earth Impurities

Shallow thermal donors in silicon doped with isotopic oxygen

The shallow thermal donors (STDs) in silicon doped with isotopic oxygen 16O and 18O have been investigated. The sample annealed at 1275°C for 4 h in a nitrogen ambient was measured by a Fourier transform infrared (FTIR) spectrometer at 10 K. In comparison, a nitrogen doped Czochralski (NCZ) silicon sample in which nitrogen–oxygen complexes existed was also checked by the FTIR spectrometer. It was found that STDs were formed in the oxygen isotope doped silicon during annealing at high temperature. It is considered that nitrogen could be involved in the generation of STDs. The line positions of the STDs were almost the same as that of the N–O complexes in NCZ silicon. The small shift of some absorption lines of STDs was also observed. In addition, a new unidentified shallow center was found and discussed.

Early stages of oxygen aggregation and thermal donors in silicon annealed under hydrostatic pressure

Thermal donor formation in Czochralski-grown silicon heat treated at T=450 °C under hydrostatic pressure is investigated by means of optical and electrical measurements. It has been shown that oxygen agglomeration processes in stressed Cz-Si lead to an enhanced formation of the well-known thermal double donors. This effect is believed to be due to increasing oxygen diffusivity under stress. Some important differences between the formation processes in Cz-Si annealed under normal conditions and high hydrostatic pressure are discussed.

Radiative recombination processes of thermal donors in silicon

AbstractThere is a recent, renewed attention on the possible development of optical emitters compatible with silicon microelectronic technology and it has been recently shown that light emitting diodes could be manufactured on dislocated silicon, where dislocations were generated by plastic deformation or ion implantation. Among other potential sources of room temperature light emission, compatible with standard silicon-based ULSI technology, we have studied old thermal donors (OTD), as the origin of their luminescence is still matter of controversy and demands further investigation.In this work we discuss the results of a spectroscopical study of OTD using photoluminescence (PL) and Deep Level Transient Spectroscopy (DLTS) on standard Czochralsky (Cz) silicon samples and on carbon-doped samples.We were able to show that their main optical activity, which consists of a narrow band at 0.767 eV ( P line), is correlated to a transition from a shallow donor level of OTD to a deep level at EV+0.37 eV which is tentatively associated to C-O complexes. As we have shown that the P line emission persists at room temperature, we discuss about its potentialities to silicon in optoelectronic applications.