Minority-carrier lifetime in dielectrically isolated single-crystal silicon films defined by electrochemical etching

The minority-carrier lifetime has been measured in thin, dielectrically isolated single-crystal silicon films defined by electrochemical etching. Both transient-current measurements on deep-depletion MOS transistors and recombination-current measurements on bipolar junction transistors have been use to determine the lifetime. Values of the order of 1 μ sec have been observed in both n-and p-type films with dopant concentrations of about 10¹⁵ cm^?3. It was found that the characteristics of the MOS transistors were not dominated by generation at either surface of the thin film. No differences were seen between the characteristics of bipolar transistors fabricated in the thin films and those of transistors fabricated in bulk control wafers.     

Minority-carrier diffusion coefficients and mobilities in silicon

A new method for accurate measurement of minority-carrier diffusion coefficients in silicon is described. The method is based on a direct measurement of the minority-carrier transit time through a narrow region of the p-n junction diode. The minority-carrier mobility is obtained from the diffusion coefficient using the Einstein relation. The method is demonstrated on low-doped n- and -p-type Si (dopings ∼10¹⁵cm^-3) and is compared with the literature data for the majority-carrier mobilities. The results show that in low-doped Si the electron minority- and -majority-carrier mobilities are comparable, but the hole minority-carrier mobility is significantly higher (∼30 percent) than the corresponding majority-carrier value. The results confirm earlier data of Dziewior and Silber.     

Minority-carrier lifetime measurements on silicon solar cells using Iscand Voctransient decay

Measurements of the transient decay of short-circuit current and open-circuit voltage of solar cells provide sufficient information, in principle, to determine both the effective back-surface recombination velocity S and the base minority-carrier lifetime τ. The practical use of the method is illustrated by an example, and the technique is applied to a variety of cells. Analysis of the effect of different cell thickness on the measurement is included. Finally, some limitations, both fundamental and experimental, are discussed.     

Large diameter silicon technology and epitaxy

The intermediate results of Super Silicon Crystal project are introduced to serve a production platform of 400 mm silicon. SSi has already installed a 400 mm CZ furnace. Raw materials are sufficiently applicable for 36 inch hot zone. We discuss a contact part between a crystal suspending system and a subsidiary cone. A successful handling system for a fragile quartz crucible and for a heavy silicon crystal is also described. A wire saw for 400 mm wafers has already been installed in SSi and sliced 400 mm wafers are demonstrated. For 400 mm epitaxial wafers, we describe pretreatment for epitaxial growth at low temperature.     

Carrier lifetime limitation defects in polycrystalline silicon ribbons grown on substrate (RGS)

Carrier lifetime limitation defects in polycrystalline silicon ribbons have been examined in samples with high oxygen and carbon content. Infrared spectroscopy showed that essentially all supersaturated oxygen impurities precipitated within 1 h annealing at over 800 °C. Preferential defect etching revealed that a much higher density of oxygen precipitates were generated in dislocation-free grains than in those highly dislocated (10⁵–10⁷ cm⁻²) ones. Correlated with electron-beam-induced current imaging, we found that oxygen precipitates are the dominant carrier recombination defects in dislocation-free grains, while dislocations are the lifetime killer for highly dislocated grains. It is suggested that eliminating dislocations alone will not improve the carrier lifetime, considering that a higher density of oxygen precipitates formed in the absence of dislocation-related heterogeneous nucleation sites will significantly degrade the carrier lifetime.     

Anisotropy of the solid-state epitaxy of silicon carbide in silicon

A new method for the solid-state synthesis of epitaxial layers is developed, in which a substrate participates in the chemical reaction and the reaction product grows not on the substrate surface, as in traditional epitaxial methods, but inside the substrate. This method offers new opportunities for elastic-energy relaxation due to a mechanism operating only in anisotropic media, specifically, the attraction of point defects formed during the chemical reaction. The attracting point centers of dilatation form relatively stable objects, dilatation dipoles, which significantly reduce the total elastic energy. It is shown that, in crystals with cubic symmetry, the most favorable arrangement of dipoles is the 〈111〉 direction. The theory is tested by growing silicon carbide (SiC) films on Si (111) substrates by chemical reaction with carbon monoxide CO. High-quality single-crystal SiC-4H films with thicknesses of up to 100 nm are grown on Si (111). Ellipsometric analysis showed that the optical constants of the SiC-4H films are significantly anisotropic. This is caused not only by the lattice hexagonality but also by a small amount (about 2–6%) of carbon atoms remaining in the film due to dilatation dipoles. It is shown that the optical constants of the carbon impurity correspond to strongly anisotropic highly oriented pyrolytic graphite.     

Supersonic jet epitaxy of silicon carbide on silicon using methylsilane

Cubic SiC thin films have been epitaxially grown on silicon substrates using the single source precursor methylsilane (H₃Si–CH₃). Single phase films were grown by supersonic jet epitaxy (SJE) at temperatures as low as 560°C on Si(111) and 600°C on Si(001). Growth rates and crystal quality were found to be strongly dependent on substrate temperature and methylsilane kinetic energy. Films were characterized by X-ray diffraction (XRD) and cross-sectional transmission electron microscopy (XTEM).     

Diffusivity and growth rate of silicon in solid-phase epitaxy with an aluminum medium

Using the classical diffusion equation for an amorphous (a)-Si---Al---Si sandwich structure, we have measured the diffusivity of a-Si in Al between 470–570°C and have derived the mass-transfer coefficient under the equilibrium solid-phase epitaxial growth condition. Our data can be used to explain recent results of junction formation by solid-phase epitaxy. The activation energy of this process is found to be 0.80 eV.     

The carrier lifetime of heat-treated silicon crystals

Carrier lifetime measurements were performed on crucible-grown, float-zoned, and swirl-free float-zoned silicon single crystals after annealing up to about 1000°C. In dislocation-free, crucible-grown silicon one pronounced maximum of the carrier lifetime can be found after annealing at 450°C . This gettering effect is correlated to the appearence of numerous IR-absorption bands at 80 K. The absorption coefficients of these bands depend on the oxygen concentration of the crystals and on the annealing duration. A differing number of maxima of the carrier lifetime after annealing at various temperatures can be found in dislocation-free, float-zoned silicon. These maxima are correlated to still remaining lattice defects in the crystals such as vacancy clusters of A-and B-type. Models are presented to explain the experimental findings.     

Degradation of silicon dioxide during selective silicon epitaxy in a dichlorosilane environment

The electrical degradation of dry thermal SiO₂ upon exposure to selective silicon epitaxy using dichlorosilane has been investigated. Capacitors were fabricated with thermal gate oxides (120 to 440A thick) grown on p-type silicon (100) substrates. Prior to the gate electrode formation, the oxides were exposed to hydrogen and dichlorosilane + hydrogen anneals. Leakage current and electric field breakdowns were measured to evaluate the effects of these anneals on the SiO₂ degradation. The SiO₂ degradation occurring because of dichlorosilane exposure was studied as a function of the temperature and time. While dichlorosilane exposure at temperatures above 850°C was found to cause high leakage current and breakdowns at low electric fields for silicon dioxide films thinner than 440Å, little effect was observed as a result of hydrogen and chlorine exposures. The degradation mechanism was attributed to pinhole etching via volatile SiO formation along defects present in the as-grown SiO₂.     

Optically active layers of silicon doped with erbium during sublimation molecular-beam epitaxy

A study is made of the electrical, optical, and structural properties of Si:Er layers produced by sublimation molecular-beam epitaxy. The Er and O contents in the layers, grown at 400–600°C, were as high as 5×10¹⁸ and 4×10¹⁹ cm⁻³, respectively. The electron concentration at 300 K was ∼10% of the total erbium concentration and the electron mobility was as high as 550 cm²/(V·s). Intense photoluminescence at 1.537 μm was observed from all the structures up to 100–140 K. The structure of the optically active centers associated with Er depended on the conditions under which the layers were grown. Fiz. Tekh. Poluprovodn. 33, 156–160 (February 1999)     

Carrier recombination and lifetime in highly doped silicon

The predominance of phonon-assisted band-band Auger recombination in highly doped silicon is demonstrated by showing that no recombination mechanism involving common (unavoidable) defects in silicon can yield carrier lifetimes that are consistent with the measured lifetimes, which exhibit an inverse-quadratic doping-density dependence, and/or with their temperature dependence. Both trap-assisted-Auger and Shockley-Read-Hall recombination mechanisms are considered, and dependences of the defect density on the doping density, which are implied by theory and experiment, are accounted for.     

Minority carrier lifetime improvement by single strained layer epitaxy of InP

By applying a single LPE-grown isoelectronically doped strained layer, on top of a conventional InP wafer, a strong reduction of dislocation and deep level density occurs. As a result an improvement in minority carrier lifetime and diffusion length and a better uniformity across the wafer is achieved. This is demonstrated by the comparison of p-n diodes fabricated with and without the strained layer.     

Extended defects and polarity of hydride vapor phase epitaxy GaN

Hydride vapor phase epitaxy (HVPE) GaN layers on sapphire substrates and so-called free-standing platelets (layers removed from the sapphire) were studied by different transmission electron microscopy (TEM) techniques. Polarity, determined by convergent beam electron diffraction (CBED), and distribution of structural defects, determined by conventional TEM, are discussed. The HVPE layers were found to grow primarily with Ga-polarity. A few inversion domains (areas with N-polarity) were observed on the substrate side of one of the free-standing layers. The dominant structural defects in HVPE GaN layers are threading dislocations. A systematic reduction of their density with an increase in layer thickness was observed for all of the samples. The experimental results indicate that the density of dislocations is inversely proportional to the distance from the substrate, which agrees with the theoretical model.     

Analysis of the growth of GaN epitaxy on silicon

Due to the great potential of GaN based devices,the analysis of the growth of crack-free GaN with high quality has always been a research hotspot.In this paper,two methods for improving the property of the GaN epitaxial layer on Si (111) substrate are researched.Sample A,as a reference,only has an AlN buffer between the Si substrate and the epitaxy.In the following two samples,a GaN transition layer (sample B) and an AlGaN buffer (sample C) are grown on the AlN buffer separately.Both methods improve the quality of GaN.Meanwhile,using the second method,the residual tensile thermal stress decreases.To further study the impact of the two introduced layers,we investigate the stress condition of GaN epitaxial layer by Raman spectrum.According to the Raman spectrum,the calculated residual stress in the GaN epitaxial layer is approximately 0.72 GPa for sample B and 0.42 GPa for sample C.The photoluminescence property of GaN epitaxy is also investigated by room temperature PL spectrum.     

Selective epitaxy of cadmium telluride on silicon by MBE

CdTe B was grown on As-terminated Si(111) by molecular beam epitaxy (MBE). Nucleation and interface properties were studied by photoelectron spectroscopy, scanning tunneling microscopy, electron diffraction, and energy-dispersive spectroscopy of x-rays. Selective growth on Si(111) was investigated either by using SiO₂ as a mask, or by growing on a patterned CdTe seed layer. The highest temperature where CdTe nucleates on As-terminated Si(111) surfaces is typically in the range of 220–250°C. On a SiO₂ mask, CdTe nucleates at the same temperatures, leading to polycrystalline growth. However, homoepitaxy of CdTe is possible around 300°C. Hence, CdTe can be grown selectively on a patterned CdTe seed layer on Si(111). This is confirmed by scanning electron microscopy and scanning Auger microscopy.     

Selective low-pressure silicon epitaxy for MOS and bipolar transistor application

The selective low-pressure epitaxy is presented in this paper. In contrast to LOCOS technology, this process starts with structuring a thick field oxide by anisotropic RIE etching. Then monocrystalline silicon is grown selectively in the windows formed. Si-gate MOS transistors have been produced using this technology. In the field of bipolar transistors, reactive ion etching and selective low-pressure epitaxy has been used to optimize the Schottky collector transistor to a nearly one-dimensional structure. These transistors have been built on a submicrometer epitaxial layer.     

Measurement of minority carrier lifetime profiles in silicon

The influence of finite surface recombination velocity on the measurement of minority carrier lifetime has been studied. The method is based on measuring the phase shift between the a.c.-photocurrent of a Schottky contact and the incident light. The limit of spatial resolution has been shown by theoretical calculations to be about one diffusion length. Lifetime profiles have been measured by the use of a mercury capillary contact.     

Simultaneous doping of silicon layers with erbium and oxygen in the course of molecular-beam epitaxy

Epitaxial silicon layers codoped with erbium and oxygen were grown by molecular-beam epitaxy using a silicon sublimation source. For growing the erbium-doped silicon layers, two types of impurity sources were used: (i) erbium-doped silicon plates were used as a source of fluxes of Er and Si atoms; and (ii) metallic erbium plates were used as an impurity-vapor source in combination with the silicon sublimation source. If gaseous oxygen was used for in situ codoping with erbium and oxygen, then concentrations ranging from 10¹⁸ to 10²⁰ cm^?3 were attained. When oxygen is in the growth chamber, the erbium-entrapment efficiency of a layer increases substantially, with the surface segregation of erbium also being suppressed by oxidation.     

Minority carrier lifetime and metallic-impurity mapping in silicon wafers

Inadvertent contaminations of silicon wafers during processing steps are simulated by in-diffusion of gold and iron. Impurity concentration mappings are deduced from lifetime scan maps, with a lateral resolution of 50 μm. Such scan maps are obtained by the contactless phase shift technique, when the sample surfaces are passivated by an acqueous solution of polyvidone. The local value of gold or iron concentration are found to be in agreement with concentrations computed from deep-level transient spectroscopy results determined by means of arrays of small metal–semiconductor diodes.