Change Of Conduction Type Research Articles

Formula omitted] device characteristics on 100 MeV gold ions irradiation

Pd p-Si and Pd n-Si devices were irradiated from 100 MeV gold (7+) ions for varying doses (∼ 10 11−10 13 ions cm −2). The devices were characterized from I-V and C-V studies. It has been found that there is a change of conductivity type i.e. from n to p at a probed depth of ∼ 8 μm which is approximately the stopping range of the gold ions in silicon. A deep acceptor state (∼ 0.61 eV above V.B. edge) with a peak density of ∼ 10 9 cm −2 is observed for p-type irradiated devices at ∼ 3 μm which is attributed to the displacement damage caused by the high energy heavy ion irradiation.

Chalcopyrite Cu(In,Ga)Se 2 and defect-chalcopyrite Cu(In,Ga) 3Se 5 materials in photovoltaic PN junctions

Efficient photovoltaic action in polycrystalline solar cells based on CuInGaSe materials is postulated to rely strongly on a chalcopyrite/defect-chalcopyrite interface. Growth and fundamental properties of such materials are discussed to understand better junction formation in such devices. A change in conductivity type (from n to p) has been observed for the defect chalcopyrite materials with increased Ga content. Specifically, we found that the p-n nature of the interface in uniform Ga content absorbers is only possible at low Ga contents (< 30% relative to In). Furthermore, crystallographic data reveal significant differences in lattice size between both chalcopyrite materials as Ga is increased beyond 30% relative to In.

Processing and properties of some II–IV–V2 amorphous and crystalline semiconductors

Experimental investigations on the preparation, characterization, and properties of several bulk and thin-film ternary alloys based on the chalcopyrite II–IV–V2 semiconductors are presented. Rapid melt solidification in vacuum-sealed fused-silica tubes resulted in amorphous alloy formation in almost all compositions in the system CdGeAs2-CdSiAs2. ZnGeAs2-CdGeAs2 alloys showed very limited tendency toward amorphous phase formation. Phase separation, crystallization and electrical properties were studied for amorphous Cd-Ge-Si-As alloys by thermal analysis, transmission electron microscopy, X-ray diffraction, and Hall measurements. Rapid crystallization resulted in a reversal of conductivity type (p-to-n or vice versa). Crystallized glassy alloys showed room-temperature mobility of 64 cm2/V s, and a hole concentration of 1020 cm−3. The p-to-n change in conductivity type upon amorphous-to-crystal transformation suggests that these alloys can be used to fabricate p-n junction devices by surface crystallization of the amorphous phase.

Electrical and optical properties of thin Fe 1− xCo xSi 2 films

Thin Fe 1− x Co x Si 2 films were prepared by DC sputtering of Co-doped silicide targets and deposition onto heated quartz substrates. Electrical measurements for the determination of resistivity and Hall coefficient were performed in the temperature range from 300 to 25 K by a van der Pauw method. The Hall mobility at room temperature is below 1 cm 2 V −1 s −1, indicating a strong influence of the impurities in the samples on the electrical transport properties. The nonlinear dependence of the Hall resistivity versus the magnetic field at low temperatures is explained by a model assuming magnetic ordering. The sign of the Hall coefficient changes from positive to negative with increasing Co concentration in the films. This could be explained by an increasing of the donor concentration in the samples. The observed change of conduction type from n to p in Co-doped samples shifts to lower temperatures by increasing the silicon content. The optical determined direct gap energy shifts linearly with increasing of the Co concentration to lower energies. This result is explained in terms of a virtual crystal field approximation including compositional disorder.

Less than 10 defects/ cm2 · μm in molecular beam epitaxy grown GaAs by arsenic cracking

Drastic reduction of irregular defect density in molecular beam epitaxy (MBE) grown GaAs is obtained by using a novel arsenic Knudsen effusion cell with a cracking furnace. A surface defect density of less than 10 cm −2 is routinely achieved for continuously grown three 3-inch diameter, 1.7 μm thick, metal-semiconductor-field effect transistor (MESFET) structures when the cracking is carried out at about 700°C, which is the critical temperature for the conduction type change, and with the group III Knudsen cell only heated near the orifice of the crucible (top heat cell). These optimized cracking conditions also lead to successful mass production of some microwave devices with not only ultra-low defect density but suitable electrical performances.

Less than 10 defects/cm2·μm in molecular beam epitaxy grown GaAs by arsenic cracking

Drastic reduction of irregular defect density in molecular beam epitaxy (MBE) grown GaAs is obtained by using a novel arsenic Knudsen effusion cell with a cracking furnace. A surface defect density of less than 10 cm−2 is routinely achieved for continuously grown three 3-inch diameter, 1.7 μm thick, metal-semiconductor-field effect transistor (MESFET) structures when the cracking is carried out at about 700°C, which is the critical temperature for the conduction type change, and with the group III Knudsen cell only heated near the orifice of the crucible (top heat cell). These optimized cracking conditions also lead to successful mass production of some microwave devices with not only ultra-low defect density but suitable electrical performances.

The change of the electric conductivity type in crystals of Bi2−xInxTe3 solid solutions

Room-temperature values of the Hall constantRH (B∥c), Seebeck coefficient α (ΔT⊥c), and the temperature dependence of the electric conductivity σ⊥c in the 120–360 K temperature interval have been investigated on samples of Bi2−xIn x Te3 crystals prepared by the Bridgman technique. It has been established on the basis of the changes of these transport coefficients with increasing content of indium that for values close tox=0.1 the conductivity type changes from p-type to n-type. Suppression of the concentration of holes due to the incorporation of In atoms into the crystal lattice of p-Bi2Te3 is accounted for by a model of point defects in the Bi2−xIn x Te3 crystal lattice. It is assumed that the arising uncharged substitutional In Bi x defects polarize the Bi2Te3 lattice and thus lower the concentration of anti-site defects Bi′Te, whose charges are compensated by holes. The dominant defects in the crystal lattice of n-Bi2−xIn x Te3 are the tellurium vacancies V Te . .

Structural aspects of non-stoichiometry and heavy doping of GaAs

Abstract A novel X-ray diffraction method X-ray quasi-forbidden reflection (XFR) intensity measurements has been developed for the analysis of structural features of both non-stoichiometry and heavy doping in GaAs. Non-stoichiometry of the order of 10−4 with higher atomic concentrations in the arsenic atomic plane was found for liquid-encapsulated-Czochralski (LEC) grown bulk GaAs, which has a close correlation with etch pit density. The XFR method was also successfully applied to direct analysis of the lattice location of doped impurities and microscopic strain around them for aluminum, indium, zinc, silicon and carbon dopants. In films deposited by molecular beam epitaxy (MBE) onto (100) and (111)B substrates, most doped silicon atoms occupy gallium sites even at high doping concentrations up to [ Si ]≈10 20 cm−3, and the carrier saturation is due to SiGa complexes. Further, occupation sites of silicon depend on the substrate orientation, and growth on a vicinal surface of (111)A results in a drastic change in conduction type. In metal-organic MBE grown GaAs, nearly complete activation of carbon atoms as acceptors and microscopic strain around CAs were directly observed up to carrier concentrations of 5 × 10 20 cm −3 .

Semiconductor chemical sensors for determination of fluorine gas concentrations

The sensitivity of semiconductor gas sensors based on tin dioxide and ferric oxide to molecular fluorine is studied. Sensors fabricated by using both thin film (magnetron sputtering) and thick film technology are investigated. It was found that SnO 2-based thin film sensors have the best sensitivity to F 2 among the samples tested (ZnO, Fe 2O 3, SnO 2, LaF 3). The minimum F 2 concentration detected by this SnO 2 film is about 0.5 ppm and we hope to reduce it to 50 ppb by technology perfection. The sensor is not sensitive to HF. The temperature range of the maximum sensitivity of SnO 2 is 240– 275 °C, and the concentration range in which a stable and reproducible signal is observed is 0.5–250 ppm. The characteristic time for the desorption process is 10 sec. at 270 °C. The mechanism of SnO 2 sensitivity to fluorine lies in the reaction of F 2 molecule with V 0 (lattice oxygen vacancies) in the surface layer of tin dioxide, with corresponding electron transfer and decrease of electron concentration in the conductivity zone. The electrophysical properties of the sensor system α-Fe 2O 3+20% SnO 2 in interaction with fluorine were also studied. In the temperature interval of 270–300 °C the change of conductivity type from n with increasing layer resistivity in F 2 to p with decreasing resistivity is observed. The intermediate type of conductivity change consists of the change of resistance from increasing (first step, τ≿~3 sec) and second step (the resistance decrease, τ≿~20 sec at 280 °C). The characteristics of this transition process are determined by both temperature and the concentration of fluorine in mixtures. We describe the situation as the inverted surface carriers layer formation by the filling of ‘strong’ surface acceptor state: e −+1/2F 2→F − surface

Heavily carbon-doped p-type InGaAs by MOMBE

Carbon-doped In x Ga 1− x As layers ( x=0−0.96) were grown by metalorganic molecular beam epitaxy (MOMBE) using trimethylgallium (TMG), solid arsenic (As 4) and solid indium (In) as sources of Ga, As and In, respectively. The carrier concentration is strongly affected by growth temperature and indium beam flux. Heavy p-type doping is obtained for smaller In compositions. The hole concentration decreases with the indium composition from 0 to 0.8, and then the conductivity type changes from p to n at x=0.8. Hole concentrations of 1.0×10 19 and 1.2×10 18 cm -3 are obtained for x=0.3 and 0.54, respectively. These values are significantly higher than those reported on carbon-doped In x Ga 1− x As by MBE. Preliminary results on carbon-doped GaAs/In x Ga 1− x As strained layer superlattices are also discussed.

Conductivity type change in MeCr 2S 4 spinels : Analysis of the energy band structure peculiarities

A joint X-ray spectroscopy and theoretical investigation of chromium chalcogenide spinels energy structure was carried out. The emission and absorption (XANES) sulphur X-ray spectra of CdCr 2S 4 and CuCr 2S 4 were obtained. The electronic structure of [CrS 6] 9- and [CuS 4] 6- fragments reproducing the real environment of transition metals in these materials was calculated by using the self-consistent field X α-SW method. The change from the semiconducting phase in CdCr 2S 4 to the metallic phase in CuCr 2S 4 is due to the appearance of partially occupied S p-and Cu d-states band in the energy gap between the occupied and unoccupied bands formed by the sulphur p- and chromium d-states.

Conductivity-type conversion in multiple-implant/multiple-anneal SOI

Results of an investigation of the electrical properties of superficial silicon and epitaxial capping layers grown on multiple-implant/anneal SIMOX and zone melt recrystallization substrates are presented. An unexpected SIMOX conductivity type change (from n to p) was observed in the SIMOX superficial layer, as well as in subsequently grown epi-layers. It is believed that the conductivity-type change is related to the presence of a process-induced acceptor impurity or an impurity (oxygen)-vacancy complex. >

Surface-contamination-related thermal instability in GaAs

The instability of the electrical properties of semi-insulating GaAs materials has been investigated. The presence of chemical contaminants on the surface of the finished wafers is responsible. Simulated thermal conversion using intentional carbon-ion implantation indicates larger concentrations for the possible contaminants on the surface than that in the bulk. The contribution to instability due to preferential gettering of imperfections from bulk by the implant and annealing process was eliminated using intentional Ar-ion implantation. For the samples which exhibited a change in electrical conduction type, a linear relationship between the thickness of the type-converted surface layer and the square root of heat treatment time was observed. It is proposed that the causes for the instability are governed by conventional diffusion mechanisms with multiple electrically active species involved. A positive correlation was also observed between thermally induced electrical instability in ion-implanted material and a reduction in activation, peak carrier density, and Hall mobility.

Electrical characterisation of Si-doped GaAs 0.5 Sb 0.5 on InP grown by molecular beam epitaxy

Between the growth temperatures of 490-520 degrees C Si-doped GaAs/sub 0.5/Sb/sub 0.5/ changes from 1*10/sup 17/ cm/sup -3/ n-type to 2*10/sup 17/ cm/sup -3/ p-type. The scattering mechanisms of the n and p-type epilayers are investigated. The reproducibility and potential applications of the observed conduction type change are demonstrated by the fabrication of a pn diode.

Electrical properties of n-type semiconducting chalcogenide glasses in the system Pb-Ge-Se

The electrical properties such as thermoelectric power, electrical conductivity and drift mobility have been studied on the chalcogenide glasses in the system Pb-Ge-Se. It has been found that the glasses in a certain composition range exhibit n-type conduction, as the second case in chalcogenide glasses, following the Bi-containing glasses. There were little differences in the electron and hole drift mobilities in a given glass, regardless of its conduction type. Above finding implies that the change in conduction type is not related to the relative drift mobilities of electrons and holes, but to the shift of the Fermi level toward the conduction band. The appearance of n-type conduction has been discussed in terms of chemical bonds.

Some electric properties of PLZT ceramics

The measurement results of permittivity, loss tangent, remanent polarization and electric conductivity of Pb(Zr0.52Ti0.48)O3 ceramics with La doping up to 10% are presented. The type of electric conductivity is determined by using the Seebeck coefficient measurement method. Marked decrease of electric conductivity has been found with increasing La content as well as the change of conductivity type in samples containing more than 7% of La.

Photoconductivity of vitreous chalcogenides chemically modified by bismuth

Photoconductive properties, such as the spectral response and the excitation intensity and temperature dependences were investigated in the Ge 20Bi xSe 80−x (X=0−13) system, which shows n-type conduction for × ≧9. The increase in Bi content caused the increase in photoconductivity, accompanied by the change of conduction type from p to n. It was found that the recombination processes of photocarriers were monomolecular and bimolecular in low and high excitation intensity regions, respectively, the processes being affected by localized states in the mobility gap. Relatively large activation energies for photoconduction were obtained in n-type samples.

Photoconductivity of n-type semiconducting chalcogenide glasses in the systems Ge20BixSe80-x and Ge20BixSe70-xTe10.

Photoconductive properties such as spectral response, light-intensity dependence and photosensitivity were studied, in parallel with optical absorption characteristics, on chalcogenide glasses in the systems Ge20BixSe80-x (x=0-13) and Ge20BixSe70-xTe10 (x=0-11); the glasses were n-type semiconductors for x>7.5 and p-type ones for x≤7.5 in both systems. The glasses, except for the case of low concentration of Bi, showed two peaks in the spectral response. The photon energies of the lower-energy peaks, which corresponded to the fundamental optical absorption, were almost constant against the increase in Bi content, indicating the constancy of optical band gaps. The higher-energy peaks are related to the contact effect between the glasses and electrodes. The photoconductivity increased with light intensity in the form of a power law. The values of exponent implied that the recombination process of photoexcited carriers was monomolecular in the low light-intensity region and bimolecular in the high-intensity region. The increase in photosensitivity, accompanied by the change of conduction type, was observed. This observation indicates that these chalcogenide glasses are promising as photoconductive materials.

Electrical and optical properties of n-type semiconducting chalcogenide glasses in the system Ge-Bi-Se

The glass-forming region was determined for the system Ge-Bi-Se; 13 at.% Bi was found to be incorporated at its maximum content into glasses, the Ge content of which was 20 at.%. Electrical resistivity, thermoelectric power, and optical absorption coefficient were measured mainly on a series of Ge20BixSe80−x glasses (x=0 –13). The resistivity decreased by about four orders of magnitude between x=9 and 10, and remained almost constant for x?10. The thermoelectric measurement showed the change of conduction type from p to n, accompanied by the above-mentioned abrupt decrease of resistivity. In n-type glasses, hopping conduction in the tail of localized states was proposed in parallel with conduction in extended states. The optical band gap was very slightly changed with the incorporation of more than 2.5 at.% Bi, in contrast to the remarkable decrease in the activation energy for conduction between x=9 and 10. The discussion based on the concentration of covalent bonds formed in the glasses led to the conclusion that the formation of a fairly large number of Bi-Se bonds and the disappearance of Se-Se bonds near x=10 were closely related to the composition dependence of the electrical and optical properties of the glasses in the present system.

Acceptor centers in the heat-treated GaAs

Hall effect and photoluminescence measurements are made on single crystals of GaAs which were heat-treated at 1000 or 1100°C in an atmosphere of As. It is shown that by heat-treatment acceptor centers are created and four of them contribute to the change of conduction type. Energy levels and origins of these centers are discussed in comparison with the results of Kressel 1 and Munoz. 2