Progress in a-Si:H/c-Si heterojunction emitters obtained by Hot-Wire CVD at 200 °C

In this work, we investigate heterojunction emitters deposited by Hot-Wire CVD on p-type crystalline silicon. The emitter structure consists of an n-doped film (20 nm) combined with a thin intrinsic hydrogenated amorphous silicon buffer layer (5 nm). The microstructure of these films has been studied by spectroscopic ellipsometry in the UV-visible range. These measurements reveal that the microstructure of the n-doped film is strongly influenced by the amorphous silicon buffer. The Quasy-Steady-State Photoconductance (QSS-PC) technique allows us to estimate implicit open-circuit voltages near 700 mV for heterojunction emitters on p-type (0.8 Ω·cm) FZ silicon wafers. Finally, 1 cm² heterojunction solar cells with 15.4% conversion efficiencies (total area) have been fabricated on flat p-type (14 Ω·cm) CZ silicon wafers with aluminum back-surface-field contact.     

Photosensitivity of the semiconductor-turpentine heterocontact

A heterocontact between a layered semiconductor (p-type indium monoselenide) and the natural organic compound turpentine has been created and studied for the first time. The electrical properties of this system are analogous to those of the metal-dielectric-semiconductor heterostructures, turpentine behaving like a p-type material. The heterojunction possesses a significant photosensitivity in the near infrared spectral range.     

Facile fabrication of p–n heterojunctions for Cu2O submicroparticles deposited on anatase TiO2 nanobelts

In this paper, Cu₂O particle-deposited TiO₂ nanobelts with p–n semiconductor heterojunction structure were successfully prepared via a two-step preparation process to investigate electron-transfer performance between p-type Cu₂O and n-type TiO₂. Various measurement results confirm that the amount of pure Cu₂O submicroparticles, with diameters within the range of 200–400 nm and deposited on the surface of TiO₂ nanobelts, can be controlled, and that the purity of Cu₂O is heavily affected by reaction time. Visible-light photodegradation activities of Rhodamine B show that photocatalysts have little or no photocatalytic activities mainly due to their p–n heterojunction structure, indicating that there hardly appears any electron-transfer from Cu₂O to TiO₂.     

<Emphasis Type="Italic">p</Emphasis>-AgCoO<Subscript>2</Subscript>/<Emphasis Type="Italic">n</Emphasis>-ZnO heterojunction diode grown by rf magnetron sputtering

P-type transparent semiconducting AgCoO₂ thin films were deposited by rf magnetron sputtering of sintered AgCoO₂ target. The AgCoO₂ films grown by rf sputtering were highly c-axis oriented showing only (001) reflections in the X-ray diffraction pattern unlike in the case of amorphous films grown by pulsed laser deposition (PLD). The bulk powder of AgCoO₂ was synthesized by hydrothermal process. The optical bandgap was estimated as 4·15 eV and has a transmission of about 50% in the visible region. The temperature dependence of conductivity shows a semiconducting behaviour. The positive sign of Seebeck coefficient (+220 μVK⁻¹) indicates p-type conductivity. Transparent p-n heterojunction on glass substrate was fabricated by rf magnetron sputtering of p-AgCoO₂ and n-type ZnO: Al thin films. The structure of the diode was glass/ITO/n-ZnO/p-AgCoO₂. The junction between p-AgCoO₂ and n-ZnO was found to be rectifying.     

Experimental Investigation of Ferromagnetism in II–VI Disordered Semiconducting Compounds

Low temperature magnetic properties of p-type bulk (Zn,Mn)Te and n-type (Zn,Mn)O films are presented and discussed in a view of a presence of carrier-induced ferromagnetism. We argue that in insulating p-type systems only a small fraction of Mn moments are coupled in a form of ferromagnetic bubbles. We show that collectively they behave typically for superparamagnets. The metallic n-type layers exhibit a much weaker effect, yet a clear tendency towards ferromagnetism has been observed.     

Photoelectrochemical solar cell fabrication with tungsten diselenide single crystals

Recent reports on highly efficient photoelectrochemical solar cells withn-type WSe₂ have prompted us to grown-type single crystals of WSe₂ using a chemical vapour transport method. Different transporting agents have been used. It is seen that SeCl₄ transporter leads to very large single crystals ofp-type WSe₂, whereas the same transporting agent with excess amount of Se leads ton-type single crystals. PEC solar cells fabricated withp-type andn-type crystals thus grown have been reported and the results discussed.     

Effective and practical h–p-version adaptive analysis procedures for the finite element method

Two practical and effective, h–p-type, finite element adaptive procedures are presented. The procedures allow not only the final global energy norm error to be well estimated using hierarchic p-refinement, but in addition give a nearly optimal mesh. The design of this is guided by the local information computed on the previous mesh. The desired accuracy can always be obtained within one or at most two h–p-refinements. The rate of convergence of the adaptive h–p-version analysis procedures has been tested for some examples and found to be very strong. The presented procedures can easily be incorporated into existing p- or h-type code structures.     

Studies on growth mechanism of HgCdTe epilayer on Si grown by HWE

In this paper, the mechanism of Hg_1−xCd_xTe/Si heterojunction grown by HWE (Hot Well Epitaxy) was studied. Opitical characterizations were shown with FTIR, the composition x = 0.39 was deduced by using MIR transmittance, the absorbing peak at 319.4 cm⁻¹ was measured by FIR transmittance, 319.4 cm⁻¹ confirmed the existence of Si–Te bond of at Si/HgCdTe interfacial layer. The I-V characteristics at both room temperature and 77 K of HgCdTe (n-type)/Si (p-type) heterojunction show that the good p-n heterojunction properties was obtained by using HWE. XRD study confirmed the formation of (111) oriented HgCdTe on (211) Si. Morphology of a cross section observed using EPMA indicates the columnar growth of HgCdTe. An analysis of interfcial layer by EPMA indicated presence of three layers composed of Si + Te, Si + Te + Hg and Si + Te + Cd + Hg. Among them, the most important one is the first layer. The problem of lattice mismatch and the difference of thermal expansion coefficient between Si and CdTe or HgTe may be improved by formation of Si–Te stable chemical bond through bybridization orbital bonding between Si and Te. The second and third layers are formed by evaporation-interdiffusion. Formation of the whole interfacial layer provides the appetency for the growth of (111) Hg_1−xCd_xTe epilayer on (211) Si substrate.     

High performance functionally graded and segmented Bi2Te3-based materials for thermoelectric power generation

Bi₂Te₃-based materials possess a figure of merit maximum over a narrow temperature range. When used in a generating mode over a large temperature difference the material operates at a substantially lower overall figure of merit than its maximum value. The conversion efficiency of a thermoelectric generator for low temperature waste heat recovery can be increased by employing functionally graded or segmented materials. In this work functionally graded p-type Bi₂Te₃-based thermoelectric materials have been prepared from melt by the Bridgman method using double doping technique. Segmented n-type thermoelement has been fabricated by joining two Bi₂Te₃-based materials with figure of merit maximum at 270 K and 380 K. The thermoelectric properties of the materials and a thermocouple comprised of p-type functionally graded and n-type segmented materials have been measured over a temperature range 200 K–450 K. The material efficiency of the thermocouple over the temperature gradient 223 K–423 K is estimated to be 10% compared with 8.8% for a standard Bi₂Te₃-based materials.     

High-performance bismuth-telluride compounds with highly stable thermoelectric figure of merit

The p-type (Bi_0.25Sb_0.75)₂Te₃ ingot doped with 8 wt% excess Te alone and the n-type Bi₂ (Te_0.94Se_0.06)₃ ingot codoped with 0.068 wt% I and 0.017 wt% Te were grown by the Bridgman method and annealed at 673 K for 5 h in a hydrogen stream. The electrical resistivity ρ, Seebeck coefficient α and thermal conductivity κ before and after annealing were measured at 298 K, so that the annealing degraded significantly ZT of the p-type specimen but enhanced remarkably that of the n-type one. The temperature dependences of ρ, α and κ of the as-grown p-type and annealed n-type specimens with higher ZT were investigated in the temperature range from 200 to 360 K. As a result, ZT values of the as-grown p-type and annealed n-type specimens have a broad peak and reached great values of 1.19 and 1.13 at approximately 320 K, respectively. The present materials were thus found to be far superior to any other bismuth-telluride compound in the thermal stability of energy conversion efficiency in addition to the high performance.     

Reproducibility and stability of N–Al codoped p-type ZnO thin films

Reproducible and stable p-type ZnO thin films have been prepared by the N–Al codoping method. Secondary ion mass spectroscopy measurements demonstrate that N and Al are incorporated into ZnO. The resistivity, carrier concentration, and Hall mobility are typically of 50–100 Ωcm, 1×10¹⁷–8×10¹⁷ cm⁻³, and 0.1–0.6 cm²/Vs, respectively, for the N–Al codoped p-type ZnO films. Hall measurement, X-ray diffraction, and optical transmission were carried out to investigate the changes of the properties with the storage period. Results show that the p-type characteristics of the N–Al codoped ZnO films are of acceptable reproducibility and stability. In addition, the N–Al codoped p-type ZnO films have good crystallinity and optical quality. The properties are time independent.     

Depth profiling of CdS homojunction using AES analysis

Top layer of spray pyrolyzedn-type CdS has been converted intop-type by diffusion of copper which resulted in the formation of homojunction. This is achieved by annealing CdS/Cu bilayer film. The nature of diffusion of copper atoms into CdS has been studied using auger electron spectroscopy (AES).     

Green synthesis of copper sulfide (CuS) nanostructures for heterojunction diode applications

Copper sulfide (CuS) rod shaped nanostructures with an average length 8 to 10 nm are synthesized through green chemical route using biodegradable starch as a capping agent under a nitrogen environment. Owing to the presence of a large number of glucose units linked by glycosidic bonds, starch can cap copper sulfide (CuS) nanoparticles. The preparation of CuS under nitrogen atmosphere produces fine quality CuS nanostructures by minimizing oxidation. XRD pattern reveals pure hexagonal covellite type CuS nanostructure with prime diffraction planes along (101), (102), (103), (006), (008), and (110) directions. The lattice parameters estimated as a?=?3.790 Å and c?=?16.51 Å. HRTEM studies show a well distribution of CuS nanorods. It shows prominent d-value of 0.28 nm corresponding to (103) hexagonal plane of CuS. The optical absorption extended up to 364 nm which is fairly blue shifted over bulk owing to the quantum confinement brought by starch. The photoluminescence emission is observed at 525 nm. The I–V measurements in planar geometry exhibit the linearity that reveals the ohmic behavior of carrier transport in CuS nanostructures. CuS nanostructures have been successfully used as effective p-type layer to fabricate sandwiched heterojunction devices with zinc chalcogenides (ZnO/ZnS and ZnS/ZnO) core/shell nanocomposites. The p-CuS/n-(zinc chalcogenides) heterojunction devices show good diode characteristics with an increase of ideality factor that may be attributed to surface defects and inhomogeneity in the barrier height. The photodetector also exhibits promising characteristics in terms of responsivity and quantum efficiency which are significant corresponding to material properties.

     

Direct bonding of silicon wafers with a diffusion layer

The possibility of solid-phase direct bonding of silicon wafers having p ⁺-or n ⁺-type diffusion layers with a high surface dopant concentration has been demonstrated for the first time. Pis’ma Zh. Tekh. Fiz. 24, 1–5 (March 26, 1998)     

Scanning Tunneling Spectroscopic Studies of the Pairing State of Cuprate Superconductors

Quasiparticle tunneling spectra of both hole-doped (p-type) and electron-doped (n-type) cuprates are studied using a low-temperature scanning tunneling microscope. The results reveal that neither the pairing symmetry nor the pseudogap phenomenon is universal among all cuprates, and that the response of n-type cuprates to quantum impurities is drastically different from that of the p-type cuprates. The only ubiquitous features among all cuprates appear to be the strong electronic correlation and the nearest-neighbor antiferromagnetic Cu²⁺-Cu²⁺ coupling in the CuO₂ planes.     

The search for novel superhard and incompressible materials on the basis of higher borides of <Emphasis Type="Italic">s</Emphasis>, <Emphasis Type="Italic">p</Emphasis>, <Emphasis Type="Italic">d</Emphasis> metals

The state of the art in the search for novel superhard and (or) incompressible materials on the basis of higher borides of s, p, d metals has been briefly reviewed. The information has been considered about experimental and theoretical studies of the following groups of borides: diborides of 4d, 5d heavy metals (Tc, Ru, Rh, Re, Os, and Ir), hexagonal tetraborides with the WB₄-type structure, and AMB₁₄ borides (where A, M are s, p metals) as well as of a number of related systems.     

Liquid phase epitaxial growth of pure and doped GaSb layers: morphological evolution and native defects

Undoped and Te-doped gallium antimonide (GaSb) layers have been grown on GaSb bulk substrates by the liquid phase epitaxial technique from Ga-rich and Sb-rich melts. The nucleation morphology of the grown layers has been studied as a function of growth temperature and substrate orientation. MOS structures have been fabricated on the epilayers to evaluate the native defect content in the grown layers from theC-V characteristics. Layers grown from antimony rich melts always exhibitp-type conductivity. In contrast, a type conversion fromp- ton- was observed in layers grown from gallium rich melts below 400 C. The electron mobility of undopedn-type layers grown from Ga-rich melts and tellurium doped layers grown from Sb- and Ga-rich solutions has been evaluated. Paper presented at the poster session of MRSI AGM VI. Kharagpur. 1995     

Determination of the laterally homogeneous barrier height of metal/p-InP Schottky barrier diodes

We have reported a study of a number of metal/p-type InP (Cu, Au, Al, Sn, Pb, Ti, Zn) Schottky barrier diodes (SBDs). Each one diode has been identically prepared on p-InP under vacuum conditions with metal deposition. In Schottky diodes, the current transport occurs by thermionic emission over the Schottky barrier. The current–voltage characteristics of Schottky contacts are described by two fitting parameters such as effective barrier height and the ideality factor. Due to lateral inhomogeneities of the barrier height, both characteristic diode parameters differ from one diode to another. We have determined the lateral homogeneous barrier height of the SBDs from the linear relationship between experimental barrier heights and ideality factors that can be explained by lateral inhomogeneity of the barrier height. Furthermore, the barrier heights of metal–semiconductor contacts have been explained by the continuum of metal-induced gap states (MIGS). It has been seen that the laterally homogeneous barrier heights obtained from the experimental data of the metal/p-type InP Schottky contacts quantitatively confirm the predictions of the combination of the physical MIGS and the chemical electronegativity.     

Materials based on bismuth and antimony chalcogenides for thermoelectric cooler stages

To enhance the efficiency of multistage thermoelectric coolers, extruded materials based on p- and n-type solid solutions of bismuth and antimony chalcogenides have been optimized for particular temperatures in the range 100–300 K. We have studied the effect of selenium doping on the thermoelectric efficiency of the p-type materials. We have fabricated pilot micromodules and compared calculated and experimentally determined characteristics (maximum temperature difference and thermoelectric figure of merit) of the modules in the range 100–300 K.     

Transiently triggered latch-up in cmos twin-tub and epitaxial technologies

We present in this work an analysis of transiently triggered latch-up in test-structures fabricated using a twin-tub process implemented on two different substrates: a p-type and a p p⁺ epitaxial one. Steady-state electrical characterization confirmed the well-known increased latch-up resistance of epitaxial structures with respect to standard ones. In this paper it is shown that, depending on the chosen electrical configuration, when latch-up is transiently triggered, epitaxial structures may have dynamic triggering currents lower than twin-tub ones. The influence of some layout variables on turn-on threshold voltage has been investigated for all samples.