Pb<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te epitaxial films for terahertz detectors

Liquid-phase epitaxy is used to fabricate Pb_0.8Sn_0.2Te films, undoped or doped with indium to different levels. The depth profiles of the carrier density and dopant concentration in the films are measured and examined. A uniform dopant concentration to a depth of 15 μm is obtained. Electrical-conduction inversion is observed at a temperature of 77.3 K as the doping level is varied. The liquid-phase epitaxial method is shown to be a more suitable technology for the reproducible manufacture of epitaxial films with a given carrier density, such as the ones used in terahertz detectors.     

On temperature coefficient of resistance of boron-doped SiGe films deposited by sputtering

Silicon–germanium films, doped with boron, were deposited on oxidised silicon substrates by RF magnetron sputtering. The post-deposition dopant activation and film crystallisation was done by annealing in the temperature range from 580 to 900 °C. The structural changes in the silicon–germanium films caused by the presence of boron and annealing were investigated by high-resolution transmission electron microscopy. The temperature coefficient of resistance (TCR) was characterised in the temperature range from room temperature to 210 °C and correlated to the nano-structure of the films. The TCR values were explained by the contribution of different scattering mechanisms and confirmed by low-frequency noise measurement. Very low values of TCR can be obtained by selecting appropriate boron content and post-deposition annealing conditions.     

Molecular heterostructure devices composed of langmuir-blodgett films of conducting polymers

Organic heterostructures have been fabricated by alternating the deposition of monoand multilayers of undoped poly(3-hexylthiophene) and doped polypyrrole prepared by the Langmuir-Blodgett technique. The dopant profiles of the structures have been electrically characterized by incorporating the polymer layers as the active semiconductive material into metal-insulator-semiconductor and Schottky barrier device configurations. The dopant concentrations were evaluated by capacitance-voltage measurements. The results indicate modulated dopant profiles and a possible transfer of dopants. The dopant concentrations differ by about an order of magnitude between the undoped and doped layers. The Schottky barriers become thinner the closer the doped polypyrrole monolayer lies to the Schottky electrode.     

n‐Type Doping of Organic Thin Films Using Cationic Dyes

We present an approach to stable n‐type doping of organic matrices using organic dopants. In order to circumvent stability limitations inherent to strong organic donors, we produce the donor from a stable precursor compound in situ. As an example, the cationic dye pyronin B chloride is studied as a dopant in a 1,4,5,8‐naphthalene tetracarboxylic dianhydride (NTCDA) matrix. Conductivities of up to 1.9 × 10^–4 S cm^–1 are obtained for doped NTCDA, two orders of magnitude higher than the conductivity of NTCDA doped with bis(ethylenedithio)‐tetrathiafulvalene as investigated previously, and four orders of magnitude higher than nominally undoped NTCDA films. Field‐effect measurements are used to prove n‐type conduction and to study the doping effect further. The findings are interpreted using a model of transport in disordered solids using a recently published model. Combined FTIR, UV‐vis, and mass spectroscopy investigations suggest the formation of leuco pyronin B during sublimation of pyronin B chloride.     

Properties of nanostructured Al doped ZnO thin films grown by spray pyrolysis technique

Aluminium doped zinc oxide thin films were deposited on glass substrate by using spray pyrolysis technique. The X-ray diffraction study of the films revealed that the both the undoped and Al doped ZnO thin films exhibits hexagonal wurtzite structure. The preferred orientation is (002) for undoped and up to 3 at % Al doping, further increase in the doping concentration to 5 at % changes the preferred orientation to (101) direction. The surface morphology of the films studied by scanning electron microscope, reveal marked changes on doping. Optical study indicates that both undoped and Al doped films are transparent in the visible region. The band gap of the films increased from 3.24 to 3.36 eV with increasing Al dopant concentration from 0 to 5 at % respectively. The Al doped films showed an increase in the conductivity by three orders of magnitude with increase in doping concentration. The maximum value of conductivity 106.3 S/cm is achieved for 3 at % Al doped films.     

Optical,morphological and electrical studies of Zn:PbS thin films

Structural, electrical, and optical properties of undoped and Zn doped lead sulfide (PbS) thin films are benign reported in this paper. The subjected films were grown on glass substrates at 25 °C by a chemical bath deposition (CBD) method. The concentration of Zn in the deposition bath represented by the ratio [Zn²⁺]/[Pb²⁺] was varied from 0% to 5%. It was found that the film׳s grains decreased in size with increasing Zn content in the film. XRD data showed the polycrystalline nature of the film its crystal orientation peak intensities decreased with higher doping concentration of Zn. Atomic force microscopy (AFM) measurements revealed that the surface roughness of the films decreased due to zinc doping as well. However, with increasing of the dopant concentration from 0% to 5%, the average transmittance of the films varied over the range of 35–75%. The estimated optical band (E_g) gaps of undoped and Zn doped PbS thin films were in the range of 0.72–1.46 eV. Hall Effect measurements electrical resistivity, carrier concentration and Hall mobility have been determined for the titled film as functions on the Zn content within the film׳s textures. The overall result of this work suggested that the Zn:PbS film is a good candidate as an absorber layer in the modern solar cell devices.     

A model of nonlinear all-optical switching in doped fibers

A theoretical model of switches utilizing the resonantly enhanced nonlinearity present in doped fibers is presented. It establishes the dependence of the switching pump power, fiber length, residual resonant signal loss, and response time of the switch on the dopant spectroscopic parameters. Simple factors of merits are derived for the power and the length requirements and are evaluated for selected rare-earth transitions. The most promising candidates require only a fraction of a mW and a few cm of fiber for full switching. Similar power characteristics, but with considerably shorter response times (ns) and lengths (sub-mm), are predicted for dopants with a high oscillator strength transition, or a power-length product ten orders of magnitude smaller than for switches based on the Kerr effect in undoped silica fibers     

The minority carrier lifetime in doped and undoped p-type Hg0.78Cd0.22Te liquid phase epitaxy films

This paper will describe: (1) the first comparative study of recombination mechanisms between doped and undoped p-type Hg_1-xCd_xTe liquid phase epitaxy films with an x value of about 0.22, and (2) the first determination of τ_A7 ⁱ/τ_A1 ⁱ ratio by lifetime’s dependence on both carrier concentration and temperature. The doped films were either copper- or gold-doped with the carrier concentration ranging from 2 x 10¹⁵ to 1.5 x 10¹⁷ cm^-3, and the lifetime varied from 2 μs to 8 ns. The undoped (Hg-vacancy) films had a carrier concentration range between 3 x 10¹⁵ and 8 x 10¹⁶ cm^-3, and the lifetime changed from 150 to 3 ns. It was found that for the same carrier concentration, the doped films had lifetimes several times longer than those of the undoped films, limited mostly by Auger 7 and radiative recombination processes. The ineffectiveness of Shockley-Read-Hall (SRH) recombination process in the doped films was also demonstrated in lifetime vs temperature curves. The important ratio of intrinsic Auger 7 lifetime to intrinsic Auger 1 lifetime, τ_A7 ⁱ/τ_A1 ⁱ, was determined to be about 20 from fitting both concentration and temperature curves. The reduction of minority carrier lifetime in undoped films can be explained by an effective SRH recombination center associated with the Hg vacancy. Indeed, a donor-like SRH recombination center located at midgap (E_v+60 meV) with a capture cross section for minority carriers much larger than that for majority carriers was deduced from fitting lifetime vs temperature curves of undoped films.     

Optimisation of a graded-index fibre over a wavelength range

The operation of graded-index fibres can be optimised in the neighbourhood of some wavelength whenever two dopants are available. Under the assumption that the index is a linear function of the dopant concentrations, a class of relations between dopants is found, which is related to that given by Olshansky.4 The case of a fibre doped with germanium and fluorine is treated.     

First-principles study of the lattice integration of palladium defects in doped germanium and silicon

Time-differential perturbed angular correlations spectroscopy of palladium in doped germanium has identified palladium-vacancy pairing in n-type antimony-doped, p-type gallium-doped and undoped germanium. In contrast, an equivalent study of palladium defects in doped silicon suggests a different scenario for the silicon host. Palladium-vacancy pairing has been proposed in n-type silicon irrespective of the dopant type (phosphorous, arsenic or antimony) but palladium–boron pairing has been speculated to occur in p-type boron-doped silicon. This thus raises the question: why does palladium pair with a dopant atom in p-type silicon, but with a vacancy in p-type germanium? Based on the density functional theory calculations carried out in this work, it is suggested that the size of the dopant and the host material both play a crucial role in determining the type of palladium-defect complex that is formed. The calculations predict a configuration with the palladium atom on a bond-centered interstitial site pairing with a semi-vacancy on either side in gallium-doped and antimony-doped silicon and germanium, respectively. Whereas, a configuration with the palladium atom on a bond-centered interstitial site pairing with the dopant was proposed in boron-doped silicon and germanium. In further support of the argument, in n-type phosphorous-doped materials the calculations predict a configuration with the palladium atom on a bond-centered interstitial site pairing with a semi-vacancy on either side in silicon, but a configuration with the palladium atom on a bond-centered interstitial site pairing with the phosphorous dopant in germanium.     

Effect of Ag in CdSe thin films prepared using thermal evaporation

It has been a general practice to dope thin films with suitable dopants to modify the properties of the films to make them more suitable for potential applications. When the dopant concentrations are low, they do not normally affect the structure and morphology of the films. However, it may lead to drastic changes in electronic properties of the films. This might result from the dopant getting incorporated into the lattice of the material of the films. Cadmium selenide is an important compound semiconductor material with an attractive energy band gap. The present work relates to an attempt made to dope CdSe thin films with silver. CdSe:Ag (1–5%) thin films were deposited on glass substrates at an optimized substrate temperature of 453 K using thermal evaporation technique. The grown films were analyzed using X-ray diffraction, scanning electron microscopy (SEM), energy dispersive analysis of X-ray (EDX) techniques. It is observed that undoped CdSe thin films and CdSe:Ag films have hexagonal structure. The grain size was found to increase marginally with an increase in the Ag concentration. The optical band gap of the films determined by optical transmission measurements agree with that of CdSe. Electrical conductivity is observed to increase from 10^–4 to 3.66 (Ω cm)^–1 on addition of silver. The variation of resistance with temperature indicates that the prepared films consist of CdSe and Ag existing as two separate phases coexisting and contributing individually to the resistivity of the films.     

An investigation of LPCVD and PECVD of in situ doped polycrystalline silicon for VLSI

In general, high-temperature processes cause thermal stresses and diffusion of dopants, resulting in reduced device yields. It is thus desirable to reduce the number of high-temperature steps and the use of an in situ doping technique eliminates one such step. In this investigation, low-pressure chemical vapour deposition (LPCVD) and plasma-enhanced chemical vapour deposition (PECVD) have been utilised to deposit in situ doped polycrystalline silicon films. The process characteristics and properties such as spreading resistance, grain structure, etch rate using a plasma and dopant concentrations of these films have been investigated and explained using a simple model for dopant activation and grain growth. It is shown that good-quality films suitable for VLSI can be produced.     

Mg and Al co-doping of ZnO thin films: Effect on ultraviolet photoconductivity

Thin films of Zinc Oxide were deposited by the sol-gel technique on glass substrates. The films were doped with Al, Mg or co-doped with both by introduction of appropriate compounds in the solution before dip-coating and annealing in air at 500 °C. Energy Dispersive X-Ray Spectroscopy was employed to measure the dopant incorporation. X-ray diffraction studies indicate that Mg doping increases grain size, while Al doping reduces it. Photoluminescence (PL) measurements indicate that undoped and Al-doped films show, along with a broad near band-edge (NBE) peak, additional peaks at longer wavelengths related to various defect states. However Mg doped films show only a sharp NBE peak, which is blue shifted compared to undoped ZnO, and there are no prominent sub band gap luminescence peaks. This is also the case for Mg and Al co-doped ZnO samples, provided the Mg content is low. Photocurrent measurements were carried out using silver contacts using a De source under atmospheric conditions. Undoped and Mg doped ZnO films showed high resistances and low photocurrent levels. With low Al doping, both the dark current and the photocurrent increase significantly, but the films show very long photocurrent transients. With optimized concentration of Mg/Al co-doping in ZnO, the photocurrent increased by ~98 times compared to ZnO films doped only with Mg. Simultaneously, the photocurrent transients became ~44 times faster than ZnO films doped only with Al.     

Characteristics of GZO thin films deposited by sol–gel dip coating

Zinc oxide (ZnO) films were deposited by sol–gel dip coating using the acrylamide route. The films were doped with different concentrations of gallium in the range 250–1200 ppm. The films exhibited hexagonal structure. The grain size decreased from 100 to 10 nm as the dopant concentration increased. The resistivity of the doped samples decreased from 10³ to 3×10⁻³ Ω cm. The band gap value shifted towards the short-wavelength region as the dopant concentration increased. XPS studies indicated doping of Ga in ZnO     

Effect of doping concentration on the grain boundary trap density and threshold voltage of polycrystalline SOI MOSFETs

PolySOI MOSFETs have been fabricated on undoped and doped polycrystalline silicon films and characterized to study the effect of doping on grain boundary passivation. The grain boundary trap density (N_ST) and threshold voltages have been extracted experimentally to evaluate the extent of grain boundary passivation by the dopants. Charge sheet model based on the effective doping concentration has been employed to analytically estimate the threshold voltages using the experimentally determined grain boundary trap density and grain size (L_g) as model parameters. The variation of threshold voltages with increasing doping concentration for the range of N_A ? (N_ST/L_g) has been studied both by simulation and experiments and the results are presented. Analytically estimated threshold voltages and experimental results show that the threshold voltage falls with increase in the dopant concentration and that this effect is indeed due to the reduction in N_ST as a result of the grain boundary passivation by the dopants.     

Electrical Behavior of <Emphasis Type="Italic">In Situ</Emphasis> Doped Polysilicon Films as Influenced by the Dopants

The dependence of the resistivity of doped polysilicon films on fabrication conditions is studied experimentally. The films are produced from a silane-germane-diborane or a silane-germane-phosphine gas mixture, being doped with germanium in combination with boron or phosphorus, respectively. The process parameters are identified that strongly influence the resistivity and temperature coefficient of resistance of the resulting films. They are (i) the volume ratio of germane to silane, (ii) the volume ratio of silane and germane to diborane and phosphine, (iii) substrate temperature, and (iv) annealing temperature. Common and distinctive features are identified in the patterns of behavior of resistivity observed in undoped and variously doped films. It is shown that film resistivity is to a large extent determined by grain size. It is also found that increasing the temperature of deposition or annealing makes for lower film resistivity.__________Translated from Mikroelektronika, Vol. 34, No. 3, 2005, pp. 172–180.Original Russian Text Copyright © 2005 by Kovalevskii, Borisenko, Borisevich, Dolbik.     

Self-organization of germanium highly ordered nanoclusters by the deposition of polycrystalline silicon films doped with germanium

Aspects of the formation of self-organized clusters of germanium (Ge) and solid solution of SiGe, first formed in the mode of deposition of subthin polycrystalline silicon films doped with Ge on the nanoscale film of dielectrics were studied by techniques of atomic force microscopy and Raman scattering by optical phonons in germanium clusters. We found that in subthin polycrystalline silicon films (PSF) doped with Ge on the nanoscale films of dielectrics in conditions of PSF film deposition, there appeared correlated spatial distribution of germanium clusters, as well as silicon rich clusters in certain conditions, i.e., clusters of SiGe solid solution, with the modes of their formation. The relationship of the form, size, and density of Ge nanoclusters (NC), with the conditions of their self-organization is considered. The influence of interdiffusion processes on self-organizing of clusters is established, which is significant at high temperatures of the deposition and doping of PSF. It was found that clusters (islands) could occur on the cleavage surface in the form of four types of topographic features in a classical pyramid form, flat-topped pyramids, and domes and sharp spines, depending on the conditions of the deposition of PSF doped with Ge. The systems of highly organized Ge NC, measuring 3.5–40 nm and with a density of 2.7 × 10⁷–3.5 × 10 cm⁻² were obtained. The possibility, in principle, of managing the geometric parameters of self-organizing NC (nanoislands) by selecting the conditions of their self-organization in the mode of deposition of PSF doped with Ge, was shown.     

稀土氧化物掺杂对Ba0.6Sr0.4TiO3-MgO复合物结构及微波介电性能的影响

研究了不同质量分数(0~1.5%)的各种稀土氧化物对Ba0.6Sr0.4TiO3(40%)-MgO(60%)陶瓷微观结构和介电性能的影响.研究表明,大半径的稀土离子掺杂能有效降低材料的介电常数并提高品质因数;而小半径的稀土离子掺杂则会提高材料的微波介电损耗.当掺杂量超过0.2%时,所有样品的调谐率都随着添加量的增加而下降.与未掺杂的BST-MgO相比,0.2%稀土掺杂样品的调谐率变化规律及机理随掺杂物的不同而不同:Nd2O3和Yb2O3 掺杂样品中调谐率的大幅度升高归因于结电容的贡献,Sm2O3 掺杂样品调谐率的下降主要由MgO晶粒的聚集所致,而Y3+同时占据A位和B位引起了样品调谐率的下降.研究发现在BST-MgO中添加具有大离子半径的稀土氧化物(如La2O3、CeO2、Nd2O3、Sm2O3)并优化其添加量,能满足铁电移相器等微波调谐器件的要求.     

Thermoelectric Properties of Ag-doped Mg<Subscript>2</Subscript>Ge Thin Films Prepared by Magnetron Sputtering

Silver doped p-type Mg₂Ge thin films were grown in situ at 773 K using magnetron co-sputtering from individual high-purity Mg and Ge targets. A sacrificial base layer of silver of various thicknesses from 4 nm to 20 nm was initially deposited onto the substrate to supply Ag atoms, which entered the growing Mg₂Ge films by thermal diffusion. The addition of silver during film growth led to increased grain size and surface microroughness. The carrier concentration increased from 1.9 × 10¹⁸ cm⁻³ for undoped films to 8.8 × 10¹⁸ cm⁻³ for the most heavily doped films, but it did not reach saturation. Measurements in the temperature range of T = 200–650 K showed a positive Seebeck coefficient for all the films, with maximum values at temperatures between 400 K and 500 K. The highest Seebeck coefficient of the undoped film was 400 μV K⁻¹, while it was 280 μV K⁻¹ for the most heavily doped film at ∼400 K. The electrical conductivity increased with silver doping by a factor of approximately 10. The temperature effects on power factors for the undoped and lightly doped films were very limited, while the effects for the heavily doped films were substantial. The power factor of the heavily doped films reached a non-optimum value of ∼10⁻⁵ W cm⁻¹ K⁻² at 700 K.     

Utilization of hole trapping effect of aromatic amines to convert polymer semiconductor from ambipolar into n-type

In this study, we added several aromatic amine compounds as dopants to an ambipolar polymer semiconductor, PDBTAZ, and studied the charge transport behavior of the doped polymer thin films in organic thin film transistors. The trap energy (E_T), which is the HOMO energy difference between the amine dopant and the polymer, was found related to the hole transport suppression effect of these amines. For an amine with E_T < 0.25 eV, at a 2% dopant concentration, little changes in the hole transport characteristics of the doped polymer films were observed. In contrast, for an amine with E_T > 0.25 eV, complete hole transport suppression was realized. This study offers a useful approach to converting an ambipolar polymer semiconductor into a unipolar n-type polymer semiconductor.