scholarly journals STUDY OF THERMOMETRIC MATERIAL Er1-xScxNiSb. II. EXPERIMENTAL RESULTS

2021 ◽  
Vol 82 (3) ◽  
pp. 5-11
Author(s):  
Volodymyr Krayovskyy ◽  
◽  
Volodymyr Pashkevych ◽  
Andriy Horpenuk ◽  
Volodymyr Romaka ◽  
...  
Keyword(s):  
Activation Energy ◽  
Low Temperature ◽  
Fermi Level ◽  
Valence Band ◽  
Structural Defects ◽  
Type Semiconductor ◽  
Thermopower Coefficient ◽  
Temperature Activation ◽  
P Type ◽  
Thermometric Material

The results of a comprehensive study of the crystal and electronic structures, kinetic and energetic performances of the semiconductor thermometric material Er1-xScxNiSb, (x=0–0.1) are presented. Microprobe analysis of the concentration of atoms on the surface of Er1-xScxNiSb samples established their correspondence to the initial compositions of the charge, and the diffractograms of the samples are indexed in the structural type of MgAgAs. Because the atomic radius Sc (rSc=0.164 nm) is smaller than that of Er (rEr=0.176 nm), it is logical to reduce the values of the unit cell's period a(x) Er1-xScxNiSb, which correlate with the results of mathematical modeling. The temperature dependences of the resistivity ln(ρ(1/T)) contain high- and low-temperature activation regions, which are specific for semiconductors and indicate the location of the Fermi level in the bandgap, and positive values of the thermopower coefficient a(x, T) specify its position – near the valence band . This result does not agree with the results of modeling the electronic structure for its ordered version. The presence of a low-temperature activation region on the ln(ρ(1/T)) p-ErNiSb dependence with an activation energy =0.4 meV indicates the compensation of the sample provided by acceptors and donors of unknown origin. A decrease in the values of the resistivity ρ(x, T) and the thermopower coefficient a(x, T) points to an increase in the concentration of holes in p-Er1- xScxNiSb in the area of concentrations x=0–0.03. This is possible in a p-type semiconductor only by increasing the concentration of the main current carriers, which are holes. The fact of increasing the concentration of acceptors in Er1-xScxNiSb at insignificant concentrations of impurity atoms is also indicated by the nature of the change in the values of the activation energy of holes from the Fermi level to the valence band . Consequently, if in p-ErNiSb the Fermi level was at a distance of 45.4 meV from the level of the valence band , then at the concentration Er1-xScxNiSb, x=0.01, the Fermi level shifted towards the valence band and was located at a distance of 13.6. Since the Fermi level reflects the ratio of ionized acceptors and donors in the semiconductor, its movement by x=0.01 to the valence band is possible either with an increase in the number of acceptors or a rapid decrease in the concentration of ionized donors. At even higher concentrations of Sc impurity in p-Er1-xScxNiSb, x≥0.03, low-temperature activation sites appear on the ln(ρ(1/T)) dependences, which is a sign of compensation and evidence of the simultaneous generation of acceptor and donor structural defects in the crystal nature. This is also indicated by the change in the position of the Fermi level in the bandgap of the semiconductor Er1-xScxNiSb, which is almost linearly removed from the level of the valence band : (x=0.05)=58.6 meV and (x=0.10)=88.1 meV. Such a movement of the Fermi level during doping of a p-type semiconductor is possible only if donors of unknown origin are generated. For a p-type semiconductor, this is possible only if the concentration of the main current carriers, which are free holes, is reduced, and donors are generated that compensate for the acceptor states. This conclusion is also confirmed by the behavior of the thermopower coefficient a(x, T) at concentrations x≥0.03. The results of structural, kinetic, and energy studies of the thermometric material Er1-xScxNiSb allow us to speak about a complex mechanism of simultaneous generation of structural defects of acceptor and donor nature. However, the obtained array of experimental information does not allow us to unambiguously prove the existence of a mechanism for generating donors and acceptors. The research article offers a solution to this problem. Having the experimental results of the drift rate of the Fermi level as the activation energy (x) from the Fermi level to the valence band by calculating the distribution of the density of electronic states (DOS) sought the degree of compensation, which sets the direction and velocity of the Fermi level as close as possible to the experimental results. DOS calculations are performed for all variants of the location of atoms in the nodes of the unit cell, and the degree of occupancy of all positions by their own and/or foreign atoms. It turned out that for ErNiSb the most acceptable option is one that assumes the presence of vacancies in positions 4a and 4c of the Er and Ni atoms, respectively. Moreover, the number of vacancies in the position Er (4a) is twice less than the number of vacancies in the position Ni (4c). This proportion is maintained for Er1-xScxNiSb. Vacancies in the positions of Er (4a) and Ni (4c) atoms Er1-xScxNiSb are structural defects of acceptor nature, which generate two acceptor zones and in the semiconductor. The introduction of impurity Sc atoms into the ErNiSb structure by substituting Er atoms in position 4a is also accompanied by the occupation of vacancies by Sc atoms and a reduction in their number. Occupying a vacancy, the Sc atom participates in the formation of the valence band and the conduction band of the semiconductor Er1-xScxNiSb, acting as a source of free electrons. We can also assume that the introduction of Sc atoms into the structure of the compound ErNiSb is accompanied by a process of ordering the structure of Er1-xScxNiSb and Ni atoms occupy vacancies in position 4c. This process also, however, 2 times slower, leads to a decrease in the concentration of structural defects of acceptor nature. In this case, Ni, giving valence electrons, now act as donors.

scholarly journals KINETIC AND ENERGETIC PERFORMANCES OF THERMOMETRIC MATERIAL TiCo1-xMnxSb: MODELLING AND EXPERIMENT

2021 ◽  
Vol 82 (1) ◽  
pp. 19-25
Author(s):  
Volodymyr Krayovskyy ◽  
◽  
Volodymyr Pashkevych ◽  
Mariya Rokomanyuk ◽  
Petro Haranuk ◽  
...  
Keyword(s):  
Solid Solution ◽  
Electronic Structure ◽  
Fermi Level ◽  
Band Gap ◽  
Conduction Band ◽  
Structural Defects ◽  
Impurity Atoms ◽  
Thermopower Coefficient ◽  
Temperature Activation ◽  
Thermometric Material

The results of a complex study of the semiconductor thermometric material TiСo1-xMnxSb, х=0.01–0.10, for the producing of sensitive elements of thermoelectric and electro resistive sensors are presented. Microprobe analysis of the concentration of atoms on the surface of TiСo1-xMnxSb samples established their correspondence to the initial compositions of the charge, and X-ray phase analysis showed the absence of traces of extraneous phases on their diffractograms. The produced structural studies of the thermometric material TiСo1-xMnxSb allow to speak about the ordering of its crystal structure, and the substitution of Co atoms on Mn at the 4c position generate structural defects of acceptor nature. The obtained results testify to the homogeneity of the samples and their suitability for the study of electrokinetic performances and the manufacture of sensitive elements of thermocouples. Modeling of structural, electrokinetic and energetic performances of TiСo1-xMnxSb, х=0.01–0.10, for different variants of spatial arrangement of atoms is performed. To model energetic and kinetic performances, particularly the behavior of the Fermi level, the band gap, the density of states (DOS) distribution was calculated for an ordered variant of the structure in which Co atoms at position 4c are replaced by Mn atoms. Substitution of Co atoms (3d74s2) by Mn (3d54s2) generates structural defects of acceptor nature in the TiСo1-xMnxSb semiconductor (the Mn atom contains fewer 3d- electrons than Co). This, at the lowest concentrations of impurity atoms Mn, leads to the movement of the Fermi level from the conduction band to the depth of the band gap. In a semiconductor with the composition TiCo0.99Mn0.01Sb, the Fermi level is located in the middle of the band gap, indicating its maximum compensation when the concentrations of ionized acceptors and donors are close. At higher concentrations of impurity Mn atoms, the number of generated acceptors will exceed the concentration of donors, and the concentration of free holes will exceed the concentration of electrons. Under these conditions, the Fermi level approach, and then the level of the valence band TiСo1-xMnxSb cross: the dielectric-metal conductivity transition take place. The presence of a high-temperature activation region on the temperature dependence of the resistivity ln(ρ(1/T)) TiСo1‑xMnxSb at the lowest concentration of impurity atoms Mn, х=001, indicates the location of the Fermi level in the band gap of the semiconductor thermopower coefficient α(Т,х) at these temperatures specify its position - at a distance of ~ 6 meV from the level of the conduction band . In this case, electrons are the main carriers of current. The absence of a low-temperature activation region on this dependence indicates the absence of the jumping mechanism conductivity. Negative values of the thermopower coefficient α(Т,х) TiСo0,99Mn0,01Sb at all temperatures, when according to DOS calculations the concentrations of acceptors and donors are close, and the semiconductor is maximally compensated, can be explained by the higher concentration of uncontrolled donors. However, even at higher concentrations of impurity Mn atoms in TiСo0,98Mn0,02Sb, the sign of the thermopower coefficient α(Т,х) remains negative, but the value of resistivity ρ(х,Т) increases rapidly, and the Fermi level deepens into the forbidden zone at a distance of ~ 30 meV. The rapid increase in the values of the resistivity ρ(х,Т) in the region of concentrations х=0.01–0.02 shows that acceptors are generated in the TiСo1-xMnxSb semiconductor when Co atoms are replaced by Mn, which capture free electrons, reducing their concentration. However, negative values of the thermopower coefficient α(Т,х) are evidence that either the semiconductor has a significant concentration of donors, which is greater than the number of introduced acceptors (х=0.02), or the crystal simultaneously generates defects of acceptor and donor nature. The obtained result does not agree with the calculations of the electronic structure of the TiСo1-xMnxSb semiconductor. It is concluded that more complex structural changes occur in the semiconductor than the linear substitution of Co atoms by Mn, which simultaneously generate structural defects of acceptor and donor nature by different mechanisms, but the concentration of donors exceeds the concentration of generated acceptors. Based on a comprehensive study of the electronic structure, kinetic and energetic performances of the thermosensitive material TiСo1-xMnxSb, it is shown that the introduction of impurity Mn atoms into TiCoSb can simultaneously generate in the semiconductor an acceptor zone (substitution of Co atoms for Mn) and donor zones and of different nature. The ratio of the concentrations of ionized acceptors and donors generated in TiСo1-xMnxSb will determine the position of the Fermi level and the mechanisms of electrical conductivity. However, this issue requires additional research, in particular structural and modeling of the electronic structure of a semiconductor solid solution under different conditions of entry into the structure of impurity Mn atoms. The investigated solid solution TiСo1-xMnxSb is a promising thermometric material.

First-Principles Study on the Conductive Properties of P-Doped ZnO

2009 ◽  
Vol 79-82 ◽  
pp. 1253-1256 ◽  
Author(s):  
Li Guan ◽  
Qiang Li ◽  
Xu Li ◽  
Jian Xin Guo ◽  
Bo Geng ◽  
...  
Keyword(s):  
Fermi Level ◽  
Valence Band ◽  
Density Functional ◽  
Lattice Structure ◽  
Mulliken Charge ◽  
Total Density ◽  
Type Conductivity ◽  
Doped Zno ◽  
P Type ◽  
Conductive Properties

In the present paper, the lattice structure, band structure and density of state of pure and P-doped ZnO are calculated by first-principle method based on density functional theory. By analyzing the Mulliken charge overlap population and bond length, it is found that the bond of P-Zn is longer and stronger than O-Zn bond for PO-ZnO. But for PZn-ZnO, the O-P bond becomes shorter and more powerful than O-Zn bond. Also, weak O-O bonds are formed in this case. Our results show that the final total energy of PO-ZnO is lower than PZn-ZnO. The lattice structure of PO-ZnO is more stability than PZn-ZnO. For PO-ZnO, The Fermi level moves into the valence band, which expresses that the holes appear on the top of valence band and thus the PO-ZnO exhibits p-type conductivity. For PZn-ZnO, the Fermi level moves up to the conductor band and the total density of states shifts to the lower energy region, thus PZn-ZnO shows the n-type conductivity.

Synthesis, crystal structure and thermoelectric properties of a new metal telluride Ba3Ag3InTe6

2017 ◽  
Vol 4 (9) ◽  
pp. 1458-1464 ◽  
Author(s):  
M.-Y. Lee ◽  
D. I. Bilc ◽  
E. Symeou ◽  
Y.-C. Lin ◽  
I.-C. Liang ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Transport Properties ◽  
Valence Band ◽  
Thermoelectric Properties ◽  
Type Semiconductor ◽  
P Type

A new p-type semiconductor Ba3Ag3InTe6 with transport properties dominated by the layer [Ag3Te4]5− distributed in the valence band.

STM studies of Fermi-level pinning on the GaAs(001) surface

1993 ◽  
Vol 344 (1673) ◽  
pp. 533-543 ◽  
Keyword(s):  
Fermi Level ◽  
Valence Band ◽  
Surface Defects ◽  
Defect Density ◽  
Valence Band Maximum ◽  
Intrinsic Defect ◽  
Fermi Level Pinning ◽  
Donor States ◽  
P Type ◽  
Surface Donor

This paper reviews recent scanning tunnelling microsopy (STM) studies of Fermi-level pinning on the surface of both n- and p-type GaAs(001). The samples are all grown by molecular beam epitaxy and have a (2 x 4)/c(2 x 8) surface reconstruction. The STM has shown that on the surface of highly doped n-type GaAs(001) there is a high density of kinks in the dimer-vacancy rows of the (2 x 4) reconstruction. These kinks are found to be surface acceptors with approximately one electron per kink. The kinks form in exactly the required number to pin the Fermi-level of n-type GaAs(001) at an acceptor level close to mid gap, irrespective of doping level. The Fermi-level position is confirmed with tunnelling spectroscopy. No similar surface donor states are found on p-type GaAs(001). In this case Fermi-level pinning results from ‘intrinsic’ surface defects such as step edges. Since this intrinsic defect density is independent of doping, at high doping levels the Fermi-level on p-type GaAs(001) moves down in the band gap towards the valence band. Tunnelling spectroscopy on p-type GaAs(001) doped 10 19 cm -3 with Be shows the Fermi-level to be 150 mV above the valence band maximum

The Effects of Doping and Temperature on the Fermi Level and its Relationship to the Recrystallization Growth Velocity in Ion-Implanted Silicon

1988 ◽  
Vol 100 ◽  
Author(s):  
L. E. Mosley ◽  
M. A. Paesler ◽  
P. D. Richard
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Growth Rate ◽  
Fermi Level ◽  
Growth Velocity ◽  
Growth Process ◽  
Arrhenius Plot ◽  
Velocity Versus ◽  
Band Bending ◽  
P Type

ABSTRACTIt has been observed that doping produces an enhancement in the recrystallization growth rate of silicon made amorphous by ionimplantation. This enhancement has been attributed to a shift of the Fermi level with doping. Evidence supporting this is based on the compensating effect of implantation of n- and p-type dopants together. We have previously proposed a model of the recrystallization growth process based on the diffusion of dangling bonds. We suggested that the rate enhancement is due to band bending at the amorphous-crystalline interface produced by doping. We have calculated the change in activation energy for the recrystallization growth velocity for a number of doping concentrations as a function of temperature. The major contribution to the apparent lowering of the activation energy with doping in an Arrhenius plot of the growth velocity versus I/kT is due to the temperature dependence of the Fermi level. Experimental data are compared with the calculated results. In addition differences in the measured growth rates in thermal and laser annealed samples are discussed, with primary emphasis on the lack of a change in the activation energy with doping in the laser annealed case.

scholarly journals A Metastable p-Type Semiconductor as a Defect-Tolerant Photoelectrode

Molecules ◽  
2021 ◽  
Vol 26 (22) ◽  
pp. 6830
Author(s):  
Zahirul Sohag ◽  
Shaun O’Donnell ◽  
Lindsay Fuoco ◽  
Paul A. Maggard
Keyword(s):  
Valence Band ◽  
Crystalline Structure ◽  
Surface Oxidation ◽  
Defect Tolerance ◽  
Defect States ◽  
Powder Density ◽  
Type Semiconductor ◽  
Recombination Centers ◽  
Gap States ◽  
P Type

A p-type Cu3Ta7O19 semiconductor was synthesized using a CuCl flux-based approach and investigated for its crystalline structure and photoelectrochemical properties. The semiconductor was found to be metastable, i.e., thermodynamically unstable, and to slowly oxidize at its surfaces upon heating in air, yielding CuO as nano-sized islands. However, the bulk crystalline structure was maintained, with up to 50% Cu(I)-vacancies and a concomitant oxidation of the Cu(I) to Cu(II) cations within the structure. Thermogravimetric and magnetic susceptibility measurements showed the formation of increasing amounts of Cu(II) cations, according to the following reaction: Cu3Ta7O19 + x/2 O2 → Cu(3−x)Ta7O19 + x CuO (surface) (x = 0 to ~0.8). With minor amounts of surface oxidation, the cathodic photocurrents of the polycrystalline films increase significantly, from <0.1 mA cm−2 up to >0.5 mA cm−2, under visible-light irradiation (pH = 6.3; irradiant powder density of ~500 mW cm−2) at an applied bias of −0.6 V vs. SCE. Electronic structure calculations revealed that its defect tolerance arises from the antibonding nature of its valence band edge, with the formation of defect states in resonance with the valence band, rather than as mid-gap states that function as recombination centers. Thus, the metastable Cu(I)-containing semiconductor was demonstrated to possess a high defect tolerance, which facilitates its high cathodic photocurrents.

Low temperature chlorobenzene catalytic oxidation over MnOx/CNTs with the assistance of ozone

RSC Advances ◽  
2015 ◽  
Vol 5 (20) ◽  
pp. 15103-15109 ◽  
Author(s):  
Dongdong Jin ◽  
Zhiyuan Ren ◽  
Zhaoxia Ma ◽  
Fu liu ◽  
Hangsheng Yang
Keyword(s):  
Activation Energy ◽  
Low Temperature ◽  
Apparent Activation Energy ◽  
Catalytic Oxidation ◽  
Complete Oxidation ◽  
P Type

O3 promotes chlorobenzene catalytic oxidation over p-type MnOx/CNTs between 80–240 °C. A CB complete oxidation of 95% is achieved below 120 °C. The reaction follows the L–H mechanism with apparent activation energy of 15.0 kJ mol−1.

Effects of Processing on Structural Defects in Silicon

1984 ◽  
Vol 36 ◽  
Author(s):  
L. J. Cheng
Keyword(s):  
Temperature Dependence ◽  
Band Gap ◽  
Valence Band ◽  
Polycrystalline Silicon ◽  
Energy Levels ◽  
Structural Defects ◽  
Significant Shift ◽  
Twin Boundaries ◽  
Phosphorus Diffusion ◽  
P Type

ABSTRACTIt is found that the recombination activities of dislocation complexes and structural defects decorating twin boundaries in as-grown, p-type cast polycrystalline silicon have no observable temperature dependence in the range of 100–300 K, but the activities of these defects in phosphorusdiffused samples decrease with the increase of temperature in the same range. The results suggest that the phosphorus diffusion can cause a significant shift of energy levels of these defects toward the valence band from the middle of the band gap.

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