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1.
Effects of Bi-doping in PbTe liquid-phase epitaxial layers grown by the TDM-CVP have been investigated. For Bi concentration in the solution, xBi, lower than 0.2 at.%, Hall mobility is low. In contrast, for xBi>0.2 at.%, Hall mobility is high, while carrier concentration is in the range 1017 cm−3. However, ICP emission analysis shows that, for xBi=1.0 at.%, Bi concentration in epitaxial layer is NBi=2.3–2.7×1019 cm−3.These results indicate that Bi behaves not only as a donor but also as an acceptor; the nearest neighbor or very near DA pairs are formed. Carrier concentration for Bi-doped layers takes a minimum value at a Te vapor pressure of 2.2×10−5 Torr for growth temperature 470°C, which is coincident with that of the undoped PbTe. And broad contact pn junctions with highly Bi-doped layers easily cause laser emission compared to undoped junctions. The result suggests that the nearest lattice site Bi–Bi DA pairs behave as strong radiative centers in PbTe.  相似文献   

2.
Effects of Bi doping in PbTe liquid-phase epitaxial layers grown by the temperature difference method under controlled vapor pressure (TDM-CVP) are investigated. For Bi concentrations in the solution, xBi, lower than 0.2 at.%, an excess deep-donor level (activation energy Ed≈0.03–0.04 eV) appears, and Hall mobility is low. In contrast, for xBi>0.2 at.%, Hall mobility becomes very high, while carrier concentration is in the range of 1017 cm−3. Inductive coupled plasma (ICP) emission analysis shows that, for xBi=1 at.%, Bi concentration in the epitaxial layer is as high as NBi=2.3–2.7 × 1019 cm−3. These results indicate that Bi behaves not only as a donor but also as an acceptor, and the nearest neighbor or very near donor-acceptor (D-A) pairs are formed, so that strong self-compensation of Bi takes place. Carrier concentration for highly Bi-doped layers shows a minimum at a Te vapor pressure of 2.2 × 10−5 torr for growth temperature 470°C, which is coincident with that of the undoped PbTe.  相似文献   

3.
Electroluminescence properties of PbTe pn junctions grown under various tellurium vapor pressures are investigated. For unintentionally doped pn junctions, the luminescence bands corresponding to D-A pair and band to band transition are observed. The luminescence intensity of the band to band transition has depended on tellurium vapor pressure, which suggests nonradiative transitions through nonstoichiometric defects forming deep levels. For pn junctions with Bi-doped epitaxial layers, only one peak appears at 20∼25 meV below band to band-transition energy, which, probably, shows recombination through impurity levels or impurity band originating from Bi-doping.  相似文献   

4.
The pn junction characteristics of the PbTe epitaxial layers grown on PbTe substrates are investigated. Both the substrate crystals and the epitaxial layers are grown under controll Te vapor pressures. The ideality factors n of pn junctions decrease close to 1 in the temperature region from 40K to about 120K, but then increase with increasing temperature. The increase of n is more pronounced for higher Te vapor pressure. As a possible origin of the recombination current, deep levels with Ed=0.09 eV are found from Hall measurements for pn junctions grown under higher Te vapor pressure.  相似文献   

5.
The development of efficient red thermally activated delayed fluorescence (TADF) emitters with an emission wavelength beyond 600 nm remains a great challenge for organic light‐emitting diodes (OLEDs). Herein, two pairs of isomers are designed and synthesized by attaching electron‐donor 9,9‐diphenyl‐9,10‐dihydroacridine (DPAC) moiety to the different positions of two kinds of highly rigid planar acceptor cores (PDCN and PPDCN). Their TADF efficiencies and emission maxima (599–726 nm) are regulated by molecular isomer manipulation. Interestingly, the photoluminescence quantum yields (ΦPLs) of trans‐isomers T‐DA‐1 and T‐DA‐2 (78% and 89%) are remarkably higher than those of their corresponding cis‐isomers C‐DA‐1 and C‐DA‐2 (12% and 14%). Significantly increased ΦPL values can be explained by single crystal structures and theoretical simulation. As a result, a deep red TADF‐OLED based on T‐DA‐2 displays a maximum external quantum efficiency (EQE) of 26.26% at 640 nm. Notably, at a brightness of 100 cd m?2, the EQE value of T‐DA‐2‐based device still remains at an extremely high level of 23.95%, representing the highest value for reported red TADF‐OLEDs at the same brightness. These results provide a reasonable pathway to optimize optoelectronic properties and thereby construct efficient red TADF emitters through rational isomer engineering.  相似文献   

6.
Nanostructured thermoelectric materials   总被引:4,自引:0,他引:4  
High values of thermoelectric figures of merit ZT, ranging from ZT=1.6 at 300 K to ZT=3 at 550 K, are reported for Bi-doped n-type PbSeTe/PbTe quantum-dot superlattice (QDSL) samples grown by molecular beam epitaxy (MBE). These ZT values were determined by directly measuring Seebeck coefficients and electrical conductivities and using the low lattice thermal conductivity value (∼3.3 mW/cm-K) determined experimentally from measurements of a one-legged thermoelectric cooler. Initial experiments have also shown that high values of ZT (∼1.1 at 300 K) are achievable for complementary Na-doped p-type PbSeTe/PbTe QDSL samples, in which the conduction and valence bands mirror those in the Bi-doped Pb chalcogenides.  相似文献   

7.
We have studied the electrical properties and luminescence spectra of melt-grown CuInSe2 single crystals and the doping of the crystals with intrinsic defects and extrinsic impurities. The preparation and the properties of p-n junctions are also discussed. We find that the low temperature photoluminescence spectra of crystals as-grown or annealed between 400 and 700 C are characteristic of the conductivity type. At 77 K, p-type crystals emit in a band peaked at 1.00 eV (type A spectrum) whereas the emission of n-type crystals peaks at 0.93 eV (type B spectrum). Type A and type B spectra can be interchanged by alternate anneals in minimum or maximum Se pressure. Type B emission dominates the electroluminescence spectrum of p-n junctions. These features are explained by the appearing and disappearing of a donor level as a consequence of annealing in vacuum or in Se atmosphere. We find that Zn and Cd act as donors. Crystals doped with these impurities have electron concentrations above 1018 cm−3. Zn-dopped samples exhibit a very broad recombination band below the bandgap in photoluminescence both at 77 and 300 K.  相似文献   

8.
Ce-doped Pb1−x Ce x Te alloys with x = 0, 0.005, 0.01, 0.015, 0.03, and 0.05 were prepared by induction melting, ball milling, and spark plasma sintering techniques. The structure and thermoelectric properties of the samples were investigated. X-ray diffraction (XRD) analysis indicated that the samples were of single phase with NaCl-type structure for x less than 0.03. The lattice parameter a increases with increasing Ce content. The lower Ce-doped samples (x = 0.005 and 0.01) showed p-type conduction, whereas the pure PbTe and the higher doped samples (x = 0, 0.015, 0.03, and 0.05) showed n-type conduction. The lower Ce-doped samples exhibited a much higher absolute Seebeck coefficient, but the higher electrical resistivity and higher thermal conductivity compared with pure PbTe resulted in a lower figure of merit ZT. In contrast, the higher Ce-doped samples exhibited a lower electrical resistivity, together with a lower absolute Seebeck coefficient and comparable thermal conductivity, leading to ZT comparable to that of PbTe. The lowest thermal conductivity (range from 0.99 W m−1 K−1 at 300 K to 0.696 W m−1 K−1 at 473 K) was found in the alloy Pb0.95Ce0.05Te due to the presence of the secondary phases, leading to a ZT higher than that of pure PbTe above 500 K. The maximum figure of merit ZT, in the alloy Pb0.95Ce0.05Te, was 0.88 at 673 K.  相似文献   

9.
The search for alternative energy sources is presently at the forefront of␣applied research. In this context, thermoelectricity for direct energy conversion from thermal to electrical energy plays an important role. This␣paper is␣concerned with the development of highly efficient p-type [(PbTe)(SnTe)(Bi2Te3)] x (GeTe)1−x alloys for thermoelectric applications using spark plasma sintering (SPS). Varying the carrier concentration of GeTe was achieved by alloying of PbTe, SnTe, and/or Bi2Te3. The rhombohedral to cubic phase transition temperature, T c, was found to be sensitive to the degree of alloying. Highest power factor values (P ≤ 33 μW/cm K2) were obtained for (GeTe)0.95(Bi2Te3)0.05 composition.  相似文献   

10.
This paper presents a study of the structure of the IR reflectance spectra in the sub-gap region of lead telluride doped with indium and gallium and the Raman spectra in PbTe(In). In the Raman and reflectance spectra of PbTe(In), features are observed at a frequency of ω 0⋍120 cm−1, whose amplitude sharply increases at temperatures T below the temperature where delayed photoconductivity appears, T c⋍25 K. A similar feature at a frequency of ω 0⋍155 cm−1 is also observed in PbTe(Ga), with the amplitude of the feature sharply increasing for T>T c⋍80 K. An analysis of the resulting data makes it possible to conclude that, in contrast with classical DX centers in III–V semiconductors, the microscopic structure of the impurity centers in the two-electron (DX-like) ground state does not correspond to an impurity atom shifted from a lattice site, whereas the impurity atom is shifted from a lattice site for the metastable one-electron impurity state. Fiz. Tekh. Poluprovodn. 32, 679–683 (June 1998)  相似文献   

11.
Silicon pn diodes were fabricated by ion implantation of B and P ions with different doses and subsequent annealing processes. Room temperature photoluminescence (PL) were investigated and the factors affecting the PL intensity were analyzed. Results show that both kinds of pn diodes have PL peak centered at about 1140 nm. Dislocation loops resulted from ion implantation and annealing process may enhance the light emission of silicon pn diode due to its band quantum confinement effect to carriers. The luminescence intensity depends on the carrier concentrations in the implantation region. It should be controlled at the range of 1–6×1016 cm−3. Moreover, the PL intensities of pn diodes with furnace annealing (FA) are higher than those with rapid thermal annealing, and the annealing temperature range for FA is 900–1100 °C.  相似文献   

12.
This paper discusses how the luminescence-excitation method affects the spectral content of the emission in ZnS: Mn single crystals. It shows that the nearest neighborhood of the Mn2+ ions is associated with the elementary emission bands having maxima at the wavelengths λm=557, 578, 600, 616, and 638±2 nm in zinc sulfide crystals with different manganese concentrations. Fiz. Tekh. Poluprovodn. 32, 673–675 (June 1998)  相似文献   

13.
The room-temperature dependences of the Seebeck coefficient, Hall coefficient, electrical conductivity, charge carrier mobility, and thermoelectric power factor were obtained as a function of thickness d (d = 8 nm to 400 nm) of PbTe epitaxial layers grown by thermal evaporation in vacuum of PbTe polycrystals doped with Na onto (100)KCl surfaces and covered with an Al2O3 layer. Distinct oscillations in the d-dependences of the properties were observed and attributed to the size quantization of the energy spectra in PbTe layers. The experimental values of the oscillation period are in good agreement with the results of theoretical calculations using the effective-mass approximation and a model for a rectangular potential well with infinitely high walls. It follows from the obtained results that quantization of the energy spectrum in PbTe thin-film structures occurs not only for the electron gas but also for the hole gas.  相似文献   

14.
Following the experimentally observed Seebeck coefficient enhancement in PbTe quantum wells in Pb1−xEuxTe/PbTe multiple-quantum-well structures which indicated the potential usefulness of low dimensionality, we have investigated the thermoelectric properties of PbSexTe1−x/PbTe quantum-dot superlattices for possible improved thermoelectric materials. We have again found enhancements in Seebeck coefficient and thermoelectric figure of merit (ZT) relative to bulk values, which occur through the various physics and materials science phenomena associated with the quantum-dot structures. To date, we have obtained estimated ZT values approximately double the best bulk PbTe values, with estimated ZT as high as about 0.9 at 300 K.  相似文献   

15.
In this work, nano-structured Bi2Te3 and PbTe thermoelectric materials were synthesized separately via solvothermal, hydrothermal and low-temperature aqueous chemical routes. X-ray diffraction (XRD), field-emission scanning-electron microscopy (FESEM), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS) were used to analyze the powder products. Results showed that the as-prepared Bi2Te3 samples were all single-phased and consisted of irregular spherical granules with diameters of ∼30 nm whereas the PbTe samples were mainly composed of well-crystallized cubic crystals with average size of approximately 100 nm. Some nanotubes and nanorods were found in Bi2Te3 and PbTe samples, respectively; these were identified as Bi2Te3 nanotubes and PbTe nanorods by EDS analysis. Possible reaction mechanisms for these syntheses are discussed in detail herein.  相似文献   

16.
Phase immiscibility in PbTe–based thermoelectric materials is an effective means of top‐down synthesis of nanostructured composites exhibiting low lattice thermal conductivities. PbTe1‐x Sx thermoelectric materials can be synthesized as metastable solid solution alloys through rapid quenching. Subsequent post‐annealing induces phase separation at the nanometer scale, producing nanostructures that increase phonon scattering and reduce lattice thermal conductivity. However, there has yet to be any study investigating in detail the local chemical structure of both the solid solution and nanostructured variants of this material system. Herein, quenched and annealed (i.e., solid solution and phase‐separated) samples of PbTe–PbS are analyzed by in situ high‐resolution synchrotron powder X‐ray diffraction, solid‐state 125Te nuclear magnetic resonance (NMR), and infrared (IR) spectroscopy analysis. For high concentrations of PbS in PbTe, e.g., x >16%, NMR and IR analyses reveal that rapidly quenched samples exhibit incipient phase separation that is not detected by state‐of‐the‐art synchrotron X‐ray diffraction, providing an example of a PbTe thermoelectric “alloy” that is in fact phase inhomogeneous. Thermally‐induced PbS phase separation in PbTe–PbS occurs close to 200 °C for all compositions studied, and the solubility of the PbS phase in PbTe at elevated temperatures >500 °C is reported. The findings of this study suggest that there may be a large number of thermoelectric alloy systems that are phase inhomogeneous or nanostructured despite adherence to Vegard's Law of alloys, highlighting the importance of careful chemical characterization to differentiate between thermoelectric alloys and composites.  相似文献   

17.
Temperature dependences of resistivity, magnetic susceptibility, and charge-carrier concentration and mobility in single-crystalline PbTe:V samples with a varied impurity content are investigated. It is shown that vanadium forms a donor level located ∼20 meV below the conduction-band bottom. The electron mobility is as high as 105 cm2 V−1 s−1 in the samples with N V ≤ 0.21 at % and proves to be more than an order of magnitude higher in the samples with the highest vanadium content N V = 0.26 at %. In the same samples, the real part of the conductivity is characterized by a pronounced frequency dependence. An increase in vanadium concentration is accompanied by a decrease in the effective magnetic moment of impurity atoms. The features of electron transport in PbTe:V may be caused by a variable vanadium valence and by the effect of interimpurity correlations.  相似文献   

18.
The preparation of bismuth doped ZnSe films on silicon (1 0 0) by pulsed laser deposition (PLD) is reported. Bismuth was used as a p-type dopant source material for ZnSe. The stable p-type films with hole carrier concentration of about 1016–1018 cm?3 were obtained. By scanning electron microscopy (SEM) and X-ray diffraction (XRD), it was found that the ambient pressure during film deposition has much to do with the morphology and crystallinity of the as-deposited products. The presence of Bi in the Bi-doped ZnSe films was confirmed by the X-ray photoelectron spectroscopy (XPS) and the possibility of a BiZn–2VZn complex forming a shallow acceptor level was discussed.  相似文献   

19.
The exploration of n-type PbTe as thermoelectric materials always falls behind its p-type counterpart, mainly due to their quite different electronic band structure. In this work, elemental Sb and Cu2Te are introduced into an n-type base material (PbTe)81-Sb2Te3. The introduction of extra Sb can effectively tune the concentration of electrons; meanwhile, Sb precipitates can also scatter low-energy electrons (negatively contribute to the Seebeck coefficient) thus enhance the overall Seebeck coefficient. The added Cu2Te is found to always co-precipitate with Sb, forming an interesting Sb/CuTe core/shell structure; moreover, the interface between core/shell precipitates and PbTe matrix simultaneously shows coherent lattice and strong strain contrast, beneficial for electron transport but adverse to phonon transport. Eventually, a peak figure of merit ZTmax  ≈  1.6 @ 823K and simultaneously an average ZT  ≈  1.0 (323–823 K) are realized in the (PbTe)81Sb2Te3-0.6Sb-2Cu2Te sample, representing the state of the art for n-type PbTe-based thermoelectric materials. Moreover, for the first time the three existing forms of Cu atoms in Cu2Te alloyed PbTe are unambiguously clarified with aberration-corrected scanning transmission electron microscopy (Cs-STEM).  相似文献   

20.
The band gap of lead-europium-telluride (Pb1-x EuxTe) was determined from room temperature optical absorption measurements and increases as dEg/dx = 3.5 eV for x ≤ 0.044. Eu atoms bond strongly to a PbTe surface during MBE growth and have a small diffusion coefficient (<1 x 10−16 cm /sec at 370°C). The lattice constant of Pb1-x, Eux Te is a nonlinear function of composition, and lattice-matched growth of Pb1-x Eux Sey Te1-y, on PbTe is demonstrated. Preliminary studies of the electrical properties of Pb1-x Eux Te indicate compensation of n-type (Bi) and p-type (Tl) dopants. These results indicate that Pb1-x Eux Sey Te1-y, may be useful for obtaining diode lasers which emit at wavelengths shorter than those available from Pb1-x, Snx Te.  相似文献   

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