Showing papers on "Doping published in 1977"

Auger coefficients for highly doped and highly excited silicon

Abstract: The recombination kinetics in highly doped p‐ and n‐type silicon has been investigated at 77, 300, and 400 K through the radiative band‐to‐band recombination. The minority‐carrier lifetime depends quadratically on the doping concentration as expected for Auger recombination. The Auger coefficients at 300 K for p‐ and n‐type silicon are found to be Cp=9.9×10−32 cm6 s−1 and Cn=2.8×10−31 cm6 s−1. They are nearly independent of temperature in the range investigated. The Auger coefficient in highly excited pure silicon at 4.2 K (electron‐hole drops) is essentially the same as in highly doped silicon.

Photoelectrolysis of water in sunlight with sensitized semiconductor electrodes

Abstract: In all previous studies of the photoelectrolysis of water, very little attention has been paid to the carrier generation and transport properties of the optically active semiconductor electrode To gather such information the present work theoretically analyzes the spectral response of TiO/sub 2/ photoelectrolysis cells Comparison with experimental results allows us to determine the diffusion length of minority carriers in TiO/sub 2/ for the first time It is the hole transport that governs the spectral response curve, not the electron transport The quantum efficiency of carrier generation in TiO/sub 2/ electrodes in the photolysis mode can be increased to 80% by doping the crystals with Al The sunlight conversion efficiency has been raised to 13% from 04% reported earlier by others The spectral response of the device has been extended into the visible portion of the spectrum through sensitization of the TiO/sub 2/ with Cr dopant impurities, allowing hydrogen generation with visible light The photoelectrolytic processes associated with the impurity doped crystals are discussed 36 references

Beryllium doping and diffusion in molecular‐beam epitaxy of GaAs and AlxGa1−xAs

Abstract: p‐type doping levels of up to 5×1019 cm−3 in GaAs and 3×1019 cm−3 in Al0.3Ga0.7As have been obtained in molecular‐beam epitaxy (MBE) with Be doping. These doping levels are more than one order of magnitude higher than can be achieved with other acceptors excepting ionized Zn, and are obtained while maintaining surface morphologies comparable to those of undoped layers. Mobilities of the Be‐doped GaAs MBE layers are comparable to those obtained in liquid‐phase epitaxy (LPE) material. Mobilities of Be‐doped Al0.3Ga0.7As MBE layers studied in this experiment are lower than those measured in LPE crystals and do not increase with decreasing doping level which indicates a high degree of donor compensation in these samples. Room‐temperature photoluminescent efficiencies obtained from the p‐MBE GaAs and AlxGa1‐xAs layers grown under As‐stabilized surface conditions also are significantly lower than those of comparably doped LPE material. This lower efficiency may be related to impurity contamination specific to the dopant source and is not observed during n‐type (Sn‐doped) GaAs layer growth under otherwise identical conditions. p (Be) ‐n (Ge) junctions have been evaluated and the results indicate that Be should be a suitable dopant for device fabrication. Doping profile measurements by the differential capacitance technique show that very abrupt (half‐width ?350 A) Be doping pulses can be realized. By observing the out diffusion of Be from these doping pulses during annealing of the diodes a value of D?1×10−15 cm2/sec for the diffusion coefficient of Be at 800° was established. It is concluded that, with the possible exception of ionized Zn, Be should emerge as the preferred acceptor in MBE growth of III–V compounds.

Doped amorphous semiconductors

Abstract: The article reviews the advances that have been made during the past two years in the new field of substitutionally doped a-semiconductors, particularly a-Si. After introducing some of the basic concepts used in the treatment of a-materials, the preparation and doping of a-semiconductors from the gas phase and the role of hydrogen are discussed in some detail. Recent results on doping by ion implantation have also been included. The following sections are concerned with the effect of n and p-type impurities on the electronic transport properties of a-Si and a-Ge. The discussion is based on results from conductivity, drift mobility, Hall effect and thermoelectric power measurements and leads to the main conclusion that the donors introduce a new hopping path through the system which begins to dominate over tail-state hopping when their density exceeds about 1018 cm-3. Recent photo-conductivity and luminescence results on doped a-Si are then discussed; they give information on recombination and als...

Photoconductivity and recombination in doped amorphous silicon

Abstract: The photoconductivity αph and its dependence on incident light intensity and temperature have been investigated in a series of doped amorphous silicon specimens at a photon energy of 2 eV. Specimens were prepared by the glow discharge decomposition of silane at a substrate temperature between 500 and 550 K. Doping was achieved by the addition of controlled amounts of phosphine or diborane during deposition. The primary aim of the work has been to explore the recombination process and its dependence on the known density of state distribution using substitutional doping to control the dark Fermi levels position over a range of 0·8 eV. It is shown that [sgrave]ph attains its optimum level when at a given temperature and intensity the steady-state electron Fermi level has been moved to an energy between 0·35 and 0·30 eV below the mobility edge, ∊ c . At this stage there also occurs a transition from predominantly monomolecular to bimolecular recombination. Both effects appear to be associated with th...

Deep Level Impurities in Semiconductors

Abstract: Solids are usually divided into metals and nonmetals. In a simplified scheme we may say that nonmetals consist of insulators and semiconductors. Both can be described by energy bands separated by a forbidden energy gap Eg• Whether a nonmetal is considered to be an insulator or a semiconductor often depends on the temperature at which its properties are to be investigated or used. In this chapter we use "semi­ conductor" to mean a nonmetal with a band gap from at least a few tenths of an eV up to a maximum of 10 eV. The considerable interest in semiconductors since the 1930s has been stimulated by their technical significance. Unlikl� metals, the physical properties of semi­ conductors can be considerably modified by introducing small amounts of foreign atoms. In this manner the resistivity of a silicon crystal can be changed by about seven orders of magnitude when one-millionth of the atoms in the crystal are replaced by suitable foreign atoms. Note that impurity substitution of this magni­ tude does not affect the band gap or other basic characteristics of the host material. Moreover, depending on the kind of foreign atom, the electrical current through the crystal is carried by electrons or holes. Hence multilayer structures with different types of conductivity can be constructed by doping a semiconductor crystal in­ homogeneously, resulting in devices such as diodes, transistors, lasers, etc. Experimentally it is found that replacing an atom of the host lattice by a foreign atom results in lattice defects with physical properties depending considerably on the particular atom introduced. Good understanding of such impurity centers has been achieved at least for Si and Ge when the foreign atom belongs to the groups of the periodic table closest to that of the semiconductor. They introduce localized donor and acceptor levels in the otherwise forbidden energy gap and are often described by the effective mass theory of Kahn & Luttinger (KL-EMT) (1-3), giving a hydrogen-like spectrum of levels with binding energies En' which can be written as

Method for forming isolated regions of silicon utilizing reactive ion etching

Abstract: A method for isolating regions of silicon involving the formation of openings that have a suitable taper in a block of silicon, thermally oxidizing the surfaces of the openings, and filling the openings with a dielectric material to isolate regions of silicon within the silicon block The method is particularly useful wherein the openings are made through a region of silicon having a layer of a high doping conductivity

Hall effect and impurity conduction in substitutionally doped amorphous silicon

Abstract: Hall mobility and conductivity measurements have been made as a function of temperature on a series of n- and p-type a—Si specimens prepared by the glow discharge technique and doped with phosphorus or boron atoms. The Hall effect exhibits an interesting double reversal in sign : n-type samples show a Hall potential in the direction normally expected for holes and the opposite applies to p-type specimens. In lightly doped n-type samples, the observed Hall mobility μmH has a magnitude of about 0.1 cm2V−1see−1, essentially independent of temperature; this is in agreement with theoretical predictions for transport in the extended states. On increasing the donor density, μmH begins to show a temperature dependence which varies systematically with the doping level. The conductivity and Hall data for n-type specimens have been analysed in terms of a model with two parallel conduction paths, one in the extended electron states and the other through the localized impurity levels where transport takes pla...

Electrical conductivity and charge compensation in Nb doped TiO2 rutile

Abstract: The electrical conductivity of rutile doped with 0.04–3 at.% niobium is reported as a function of oxygen pressure in the temperature range 1273–1623 K. The charge compensation is discussed in terms of a point defect model, under the assumption of a substitutional incorporation of niobium into the titanium rutile sublattice. Two kinds of charge compensation occur according to the temperature and the oxygen pressure, via an electronic or a lattice defect, in a Ti1−yNbyO2 or a Ti1−yNbyO2+y/2 solid solution, respectively. In the overstoichiometric range of the oxide, the data, when applied to undoped rutile, allow some conclusions about the atomic or electronic transport properties, both in the high and low temperature regimes.

Effect of O2 pressure during deposition on properties of rf‐sputtered Sn‐doped In2O3 films

Abstract: The electrical and optical properties of rf‐sputtered Sn‐doped In2O3 (ITO) films have been found to depend strongly on the O2 partial pressure during deposition. For the sputtering conditions used, films with both low electrical resistivity (ρ ∼ 3 × 10−4 Ω cm) and high visible transmission (∼ 90%) were obtained only over a narrow range of O2 pressures, from 3 × 10−5 to 4 × 10−5 Torr. Our results appear to explain the difficulties that have previously been encountered in obtaining high‐quality ITO films, and indicate that control of the O2 pressure during deposition is essential for reproducible preparation of such films.

Acceptor dopants in silicon molecular‐beam epitaxy

Abstract: Epitaxial silicon films have been grown on single‐crystal Si (100) substrates by evaporation from an e‐gun source in ultrahigh vacuum and have been doped with gallium and with aluminum from separate oven sources. Gallium doping profiles have been controlled accurately for substrate temperatures in the range 600–800 °C and for carrier densities in the range 1014–5×1017 cm−3. Examples are given of abrupt changes in doping level. Measured drift mobilities in the films are within 15% of values for bulk silicon. Crystallographic properties of the films are comparable to those of the substrates and are suitable for device applications. Films doped with aluminum exhibit comparable electrical and crystallographic properties, but good control of the doping profile has not been achieved for the range of parameters studied.

Auger recombination in GaAs and GaSb

Abstract: In highly excited GaAs and GaSb luminescence bands above the band gap at $h\ensuremath{ u}={E}_{g}+{\ensuremath{\Delta}}_{0}$ are observed, which are explained by radiative recombination of Auger-excited holes in the split-off valence band with free or shallow bound conduction-band electrons. An extremely weak luminescence continuum in both materials between $h\ensuremath{ u}={E}_{g}$ and $h\ensuremath{ u}=2{E}_{g}$, which shows no distinct structure within the experimental resolution, is ascribed to the radiative recombination of relaxing Auger electrons in the conduction band. The role of the split-off valence band for hole-hole-electron (hhe) Auger recombination is explained. From spectroscopic data the hhe Auger coefficients ${C}_{p}$ for GaAs [${C}_{p}{(\mathrm{GaAs})}_{77 \mathrm{K}}\ensuremath{\approx}{10}^{\ensuremath{-}(31\ifmmode\pm\else\textpm\fi{}1)}$ ${\mathrm{cm}}^{6}$ ${\mathrm{sec}}^{\ensuremath{-}1}$] and for GaSb [${C}_{p}{(\mathrm{GaSb})}_{77 \mathrm{K}}\ensuremath{\approx}{10}^{\ensuremath{-}(25\ifmmode\pm\else\textpm\fi{}1)}$ ${\mathrm{cm}}^{6}$ ${\mathrm{sec}}^{\ensuremath{-}1}$] are estimated, in rough agreement with theoretically predicted values. The dependence of the luminescence intensities of the investigated emission bands in GaSb at ${E}_{g}$ and at ${E}_{g}+{\ensuremath{\Delta}}_{0}$ on the exciting light density and on the doping concentration leads to the conclusion that in $p$-type GaSb band-to-band Auger recombination occurs. The surprisingly high intensity of the emission, which is connected with a hhe Auger process, in $n$-type GaSb(Te) and its strange dependence on the excitation power is explained by a band-to-acceptor Auger process. It is believed that this acceptor is the doubly ionizable native defect in GaSb, which is always present.

Thermoelectric power in phosphorous doped amorphous silicon

Abstract: Thermoelectric power and conductivity measurements have been made as a function of temperature on a series of a-Si specimens doped substitutionally with phosphorous. The samples were prepared by the glow discharge decomposition of silane containing predetermined concentrations of phosphine. The thermoelectric power of all the samples investigated was negative as expected. For the lightly doped specimens the thermoelectric and conductivity results support the model developed from previous work. Electron transport is in the extended states, but below room temperature there is an increasing contribution from tail state hopping. At higher doping concentrations the data can be interpreted in terms of transport through the extended states and the localized donor states, as suggested by the analysis of recent Hall effect results. The value of the intercept S 0 on the S axis at 1/T = 0 depends strongly on the position of the Fermi energy ∊F with respect to the mobility edge at ∊c. The movement of ∊F with...

Specific heat study of heavily P doped Si

Abstract: Low temperature photoluminescence and Auger electron spectroscopy have been used to study chemical-vapor deposited SiO2 and SigN4 layers as en- capsulants for high temperature annealing of GaAs. Silicon dioxide or silicon oxynitride layers allow out-diffusion of Ga, while suitably prepared rf plasma deposited SisN4 layers can be used to anneal GaAs with negligible Ga out- diffusion. Ion implantation is a versatile method of doping semiconductors and is an established fabrication step for many silicon devices (1). Although the use of implantation in the III-V compounds is less wide- spread, important device applications have emerged. These include the fabrication of light emitting diodes (2), GaAs field-effect transistors, optical waveguid.es, and detectors (3). Because of the difficulties of selec- tively doping GaAs or other compound semiconductors by standard diffusion processes as compared with Si, it now appears that implantation will play an increas- ing role in future device applications of compound semiconductors. In view of the potential for this doping method, it is important to develop reliable procedures for im- plantation and annealing in these materials. Ion im- plantation produces considerable lattice damage which must be annealed out in order to restructure the lattice and activate the implanted impurities. While this pro- cedure is relatively straightforward in Si, annealing a compound semiconductor such as GaAs is more difficult. The incongruent evaporation of Ga and As from GaAs at temperatures ~ in excess of 600~ (4) makes it impossible to anneal bare GaAs samples without surface degradation. It is thus necessary to encapsulate the sample with a suitable dielectric layer or to perform the anneal in a carefully controlled ambient (5. 6). There have been numerous discussions of implantation and annealing in GaAs using encapsu- lants such as sputtered or chemical,vapor deposited SiO2 (7), thermally o r reactively deposited or sput- tered Si3N4 (8-10), or sputtered A1N (11). In the present work we have used low temperature photo- luminescence (PL) and Auger electron spectroscopy _(AES) to investigate the annealing-encapsulation properties of chemical vapor deposited SiO2 and rf plasma deposited Si.~N4 layers on GaAs. It is well known from diffusion experiments in Si that Ga has a very high diffusion coefficient in SiO2 (12). Gyulai et

Study of Encapsulants for Annealing GaAs

Abstract: Low temperature photoluminescence and Auger electron spectroscopy have been used to study chemical-vapor deposited SiO2 and SigN4 layers as en- capsulants for high temperature annealing of GaAs. Silicon dioxide or silicon oxynitride layers allow out-diffusion of Ga, while suitably prepared rf plasma deposited SisN4 layers can be used to anneal GaAs with negligible Ga out- diffusion. Ion implantation is a versatile method of doping semiconductors and is an established fabrication step for many silicon devices (1). Although the use of implantation in the III-V compounds is less wide- spread, important device applications have emerged. These include the fabrication of light emitting diodes (2), GaAs field-effect transistors, optical waveguid.es, and detectors (3). Because of the difficulties of selec- tively doping GaAs or other compound semiconductors by standard diffusion processes as compared with Si, it now appears that implantation will play an increas- ing role in future device applications of compound semiconductors. In view of the potential for this doping method, it is important to develop reliable procedures for im- plantation and annealing in these materials. Ion im- plantation produces considerable lattice damage which must be annealed out in order to restructure the lattice and activate the implanted impurities. While this pro- cedure is relatively straightforward in Si, annealing a compound semiconductor such as GaAs is more difficult. The incongruent evaporation of Ga and As from GaAs at temperatures ~ in excess of 600~ (4) makes it impossible to anneal bare GaAs samples without surface degradation. It is thus necessary to encapsulate the sample with a suitable dielectric layer or to perform the anneal in a carefully controlled ambient (5. 6). There have been numerous discussions of implantation and annealing in GaAs using encapsu- lants such as sputtered or chemical,vapor deposited SiO2 (7), thermally o r reactively deposited or sput- tered Si3N4 (8-10), or sputtered A1N (11). In the present work we have used low temperature photo- luminescence (PL) and Auger electron spectroscopy _(AES) to investigate the annealing-encapsulation properties of chemical vapor deposited SiO2 and rf plasma deposited Si.~N4 layers on GaAs. It is well known from diffusion experiments in Si that Ga has a very high diffusion coefficient in SiO2 (12). Gyulai et

A systematic experimental and theoretical investigation of the grain‐boundary resistivities of n‐doped BaTiO3 ceramics

Abstract: The electrical resistivities, current‐voltage characteristics, and thermopowers of a series of n‐doped BaTiO3 ceramics having systematically varying resistivity anomalies (posistor or PTC effect) are analyzed in light of the theoretical description of the grain‐boundary resistivity by a Schottky‐type potential barrier model (Heywang’s barrier). The observed current‐voltage dependences agree well with this model over a wide voltage range. However, the agreement between the theoretical and experimental temperature curves of the low‐voltage resistivities is weak if the surface acceptor states, which result as recently suggested from an excess of barium vacancies in the immediate vicinity of the grain surface, are assumed to be at the same energy. Satisfactory agreement is obtained when the acceptor states are distributed over a certain energy interval. An estimate of the surface charge then reveals that the resistivity below the Curie point is governed by a residual potential barrier originating from an exce...

Defect Structure of α-Al2O3 Doped with Titanium

Abstract: Titanium-doped α-Al2O3 exhibits a high-temperature conductivity which is ionic at high oxygen pressures and electronic at low oxygen pressures. Both are isotropic. The temperature dependence of conductivity under conditions where equilibrium with the atmosphere is not maintained indicates both the position of the energy level of titanium (TiAlx) in the forbidden gap and the temperature dependence of the mobility of the native ionic defects (Al vacancies, VAlm). Optical absorption responsible for the pink color of the reduced crystals is measured as a function of po2 and is used to determine concentrations of Ti3+ and Ti4+. Parameters for the equilibrium constants of the reactions involving electrons by which the composition of Al2O3:Ti and undoped Al2O3 is varied are determined. The chemical diffusion data by Jones et al. are described quantitatively.

Coordination of Arsenic Impurities in Amorphous Silicon-Hydrogen Alloys

Abstract: We have determined the coordination of arsenic impurities in amorphous silicon-hydrogen alloys prepared by plasma decomposition of silane-arsine mixtures. From analysis of the extended x-ray absorption fine structure (EXAFS) on the arsenic $K$-shell absorption, we find at low arsenic concentrations that an average of two arsenic atoms in ten are fourfold coordinated with silicon. This is the first direct evidence for the occurrence of substitutional doping in an amorphous semiconductor.

Ionic Conductivity of Doped Cerium Trifluoride

Abstract: The electrical conductivities of the tysonite‐type fluorides based on in the sintered state were measured for various aliovalent cation dopants. Doping of difluoride such as , , or up to 5 mole percent made the conductivity increase while the doping of tetrafluoride such as led it to decrease. These facts together with the experimental results of electrolysis indicated that the specimens were fluoride ion conductors resulting from the easy movement of fluoride ion vacancies. The activation energies for conduction at the high temperature range above 250°C were, in general, about 0.25 eV irrespective of divalent dopant species, while those at lower temperatures were depending on the dopant species. Their conductivities are, in general, higher than those of the electrolytes which are also the tysonite‐type fluorides. had the highest conductivity among the tysonite‐type fluorides ever examined.

High-resolution photoemission yield and surface states in semiconductors

Abstract: Accurate measurements of the total photoemission yield, down to the 10−11 electron per incident photon range with a resolution in energy better than 20 meV, bring new information, compared to other methods, on surface states in the gap and the upper part (∼1 eV) of the valence band of semiconductors. It is shown that the first derivative, with respect to energy, of the yield curves gives a good picture of the density of states and that experiments on differently doped samples allow us to distinguish between surface and bulk state effects. Some results obtained on cleaved Si(111), Ge(111) and GaAs(110) surfaces are discussed. In particular, on the clean surface, detailed information is obtained on intrinsic surface states and on the effect of linear defects such as steps and even of surface point defects. In the case of GaAs(110), it is experimentally demonstrated that the changes as a function of energy of the escape function for electrons excited from surface states can be neglected. Interaction with gases such as O2 or H2 brings information on sticking coefficients and allows the discussion of the influence of transition matrix elements.

Reduction of grain boundary recombination in polycrystalline silicon solar cells

Abstract: The possibility of increasing the carrier collection efficiency in polycrystalline silicon by means of a heavily doped region near the grain boundaries is investigated. Phosphorous dopant is preferentially introduced into the grain boundaries of p‐type material by a low‐temperature diffusion process. A subsequent high‐temperature diffusion forms a highly n‐doped skin covering each grain. The resulting junction around each grain surface collects electrons which might otherwise recombine at the grain boundaries. This grain boundary doping scheme makes possible an increase in the conversion efficiency of polycrystalline silicon solar cells in which the grain structure is columnar.

Interstitial doping of amorphous silicon

Abstract: Interstitial doping of glow‐discharge a‐Si has been achieved by in‐diffusion and implantation of lithium. After doping with about 1% Li, we observe an increase of room‐temperature conductivity by a factor of 106 and a decrease in the activation energy of conductivity down to 0.17 eV. Corresponding changes are observed for the thermoelectric power which, as expected for n‐type material, has a negative sign.

Determination of the wavelength of zero material dispersion in optical fibres by pulse-delay measurements

Abstract: Pulse delay measurements on fibres are reported, made over a wide wavelength range straddling the zero of material dispersion. Results for phosphosilicate and a range of germania doped fibres indicate that the wavelength of negligible material dispersion lies in the range 1270-1400 nm. The optimum wavelength depends on the concentration for fibres containing germania.

A new acceptor level in indium‐doped silicon

Abstract: A new acceptor level located 0.111±0.002 eV from the valence band with a peak photoionization cross section of (1.4±0.6) ×10−16 cm2 has been observed in indium‐doped silicon. Its presence is revealed both by the low‐temperature slope of Hall measurements versus temperature and by the spectral response of the photoconductivity. The concentration of this 0.111‐eV level is strongly correlated with the concentration of indium, suggesting that an In complex is responsible for this center.

Semiconductor photoelectric generator

Abstract: A semiconductor photoelectric generator, for converting radiation energy from a source, for example, the sun, into electric energy, comprises a matrix of photo electric converters made of a semiconductor material Each photoelectric converter is doped to form a P-N junction and an isotype junction Current-collecting conductors are connected to a base region and to an alloy region An operating surface of the semiconductor photoelectric generator is secured by a translucent adhesive layer to a coating exposed directly to radiation from a radiation source The coating is composed of optical concentrators which focus the radiation energy in a focal spot and are disposed on the operating surface so that the absorption band of the focussed radiation in the focal spot is located in the base region and is spaced from the P-N junction by a distance not exceeding the diffusion length of the minority carriers in the base region

Investigation of the energy spectrum and kinetic phenomena in dislocated Si crystals (I)

Abstract: An investigation is made of the de conductivity and the Hall effect in heavily dislocated Si crystals doped with boron (1013 cm−3) and phosphorus (2 × 1014 cm−3). In such crystals two levels are shown to exist, namely, donor-acceptor level with E1 = (0.42 ± 0.03) eV above the valence band and acceptor level with E2 = (0.43 ± 0.03) eV below the conduction band. Both E1- and E2-levels are assumed to be due to dislocations and to correspond to states of electrons localized in cores of dislocations with edge components. [Russian text Ignored.]

Methods of manufacturing semiconductor devices

Abstract: A method of manufacturing a semiconductor device is set forth in which a masking layer is formed on part of the surface of a deposited layer of a relatively high resistivity polycrystalline semiconductor material being present on an insulating layer provided at a surface of a semiconductor body or portion thereof. A relatively low resistivity conductive region having a substantially uniform narrow line width is defined in the polycrystalline layer by effecting a diffusion process to laterally diffuse a doping element into a portion of the polycrystalline layer underlying an edge portion of the masking layer without diffusing the doping element through the insulating layer into the semiconductor body or portion thereof.