P-type Samples Research Articles

The use of low-frequency current fluctuations in measuring the mobility of holes in the MEH-PPV polymer

A diagnostic method based on the evaluation of low-frequency current fluctuation spectra is presented. When measuring the current through a p-type MEH-PPV sample, the occurrence of fluctuation is observable which can be measured with an AC amplifier. A model has been proposed that proves that the fluctuations originate from the interaction between the valence band and the band gap traps. The mean value of the amplitudes of these fluctuations increases linearly with decreasing frequency with a slope from which the product of mobility and lifetime of current carriers µpτp= (9 ± 3) × 10−15 cm2V−1 was obtained. The hole lifetime of (0.27 ± 0.01) ns was evaluated from the luminescence relaxation using the time-correlated single photon counting (TCSPC) technique. The mobility value (3 ± 1) × 10−5 cm2 V−1s−1 calculated using the above methods was compared with the mobility 1.8 × 10−5 cm2 V−1s−1 determined by the CELIV method (Charge extraction by linearly increasing voltage) and good agreement was obtained.

Achieving enhanced power factor using dual substitution at Cu and S sites in tetrahedrites thermoelectric materials Cu12Sb4S13

Thermoelectric (TE) materials-based devices are valuable for translating heat into electricity, but the cost is largely driven by the use of purified metals required for efficient TE performance. This study focuses on tetrahedrite materials, which are cost-effective due to their abundance in copper ore mining waste and status as one of the most widespread sulfosalts on Earth. The research investigates the effects of co-doping and iso-valent doping on the TE properties of p-type tetrahedrite samples, specifically Cu10Mn2Sb4S11Se2 (Sample A) and Cu10MnZnSb₄S11Se2 (Sample B). These samples were synthesized using hot pressing at 773 K and compared with the existing pristine compound (Cu10Mn2Sb4S13). Doping with Mn and Zn (1:1) at the Cu site was found to optimize carrier concentration and enhance phonon scattering, leading to an improved power factor. Additionally, the Se substitution at the S site also introduced band degeneracy, further increasing the power factor. Further, sample B exhibited the highest Seebeck coefficient (∼300 μV/K) at 650 K, in comparison to Sample A (∼225 μV/K) and the pristine compound (∼250 μV/K). On the other hand, Sample A demonstrated significantly higher electrical conductivity (∼0.76 × 10⁴ S/m at 650 K), ∿ three times greater than that of the other prepared samples. Notably, the power factor of Sample A (∼0.389 mW/mK2 at 650 K) was more than twice that of Sample B (∼0.141 mW/mK2) and the pristine compound (∼0.160 mW/mK2). These findings suggest that dual-site substitution at the Cu and S positions presents a promising strategy to augment the TE performance of tetrahedrite compounds.

Investigation of Sensitive Thermal Sensors Based on Si<Pt> and Si<Pd>

In this work, new sensitive thermal sensors based on Si<Pt> and Si<Pd> were developed. Single-crystal n- and p-type silicon samples doped with phosphorus and boron during growth were used for the study. These samples were first doped with platinum and palladium, then subjected to ohmic contact with nickel. To manufacture temperature sensors based on n-Si˂Pd˃ and obtain an ohmic contact, this material was subjected to appropriate mechanical and chemical treatments. Metallic nickel with a thickness d = 1 μm was chemically deposited on its surface, followed by thermal annealing in a vacuum at T = 400-450℃ for t = 10 - 15 minutes. To compare the created temperature sensors, a special measuring device, a thermostat, was developed to ensure uniform heat transfer.

Improving thermoelectric properties in double half-Heusler M8FexNi8−xSb8 (M = TiZrHfNb)-InSb compounds via synergistic multiscale defects and high-mobility carrier injection

In this study, the modulation doping strategy combined with atomic-scale engineering is applied to the Double half-Heusler (DHH) system. Thermoelectric properties of multi-principal-element alloy Ti2Zr2Hf2Nb2FexNi8−xSb8 are first improved through composition optimization and then modulation doping with nano-InSb. First-principles calculations indicate that strong phonon anharmonicity results in low intrinsic lattice thermal conductivity (κL). Synergistic high-mobility carrier injection and multiscale defects caused by lattice distortion, sluggish diffusion effect, and inhomogeneous doping decouple electron and phonon transport that extrinsically intensified phonon scattering and optimized carrier transport. Consequently, the ZTmax values of nano-InSb doped p-type (x = 5.6) and n-type (x = 2.4) samples are 0.6 and 0.36, respectively, which increased by 663 % and 350 %, compared with the InSb-free x = 5 sample. The corresponding κL near room temperature are as low as ∼2.7 and ∼2.3 W m−1 K−1, respectively. Furthermore, the p-type composition exhibits a relatively high power factor (∼2 mW m−1 K−2), and the n-type samples show negligible bipolar effects at high temperatures. This work provides a novel strategy for the optimization of thermoelectric properties in DHH compounds.

Identification of the conductivity type of single-walled carbon nanotubes via dual-modulation dielectric force microscopy.

The conductivity type is one of the most fundamental transport properties of semiconductors, which is usually identified by fabricating the field-effect transistor, the Hall-effect device, etc. However, it is challenging to obtain an Ohmic contact if the sample is down to nanometer-scale because of the small size and intrinsic heterogeneity. Noncontact dielectric force microscopy (DFM) can identify the conductivity type of the sample by applying a DC gate voltage to the tip, which is effective in tuning the accumulation or depletion of charge carriers. Here, we further developed a dual-modulation DFM, which simplified the conductivity type identification from multiple scan times under different DC gate voltages to a single scan under an AC gate voltage. Taking single-walled carbon nanotubes as testing samples, the semiconducting-type sample exhibits a more significant charge carrier accumulation/depletion under each half-period of the AC gate voltage than the metallic-type sample due to the stronger rectification effect. The charge carrier accumulation or depletion of the p-type sample is opposite to that of the n-type sample at the same half-period of the AC gate voltage because of the reversed charge carrier type.

Extension of the scope of the photoluminescence method after electron irradiation for quantifying low-level carbon in silicon

We have extended the applicability of the photoluminescence method after electron irradiation for quantifying low-level C impurities in Si crystals. The intensity ratio of the G-line to the intrinsic emission normalized by the ratio of the reference sample is used as an index of the C concentration. The calibration curves have already been established for Czochralski-grown crystals with resistivity higher than 50 Ω·cm (n-type) and higher than 5 kΩ·cm (p-type). We showed that the method was extendable to the resistivity range down to 30 Ω·cm in n-type samples with the O concentration in the range 1–6 × 1017 cm−3. The extension to float-zone (FZ) crystals was realized by using the theoretical relationship between the C concentration and the G-line intensity ratio normalized by the ratio of the FZ reference sample. Regarding the extension to conductive p-type B-doped samples, the formation of B-related radiation-induced defects was found to be an obstacle.

Thermoelectric properties of sintered Ba2AgSi3 crystals and search for impurities to control conductivity type by first-principles calculation

In this study, the basic properties of Ba2AgSi3 were investigated in detail from both experimental and computational viewpoints. Polycrystalline Ba2AgSi3 formed by an arc-melting apparatus under an argon atmosphere was ground into powders, and then powder samples were sintered using the spark plasma sintering method. Both n-type and p-type samples were obtained. This may be due to a slight deviation from the stoichiometric composition. The energy bandgap of Ba2AgSi3 was measured to be around 0.17 eV from the temperature dependence of electrical conductivity and was in agreement with that by first-principles calculations. Sintered samples exhibited a high Seebeck coefficient of −273 μV K−1 and a high power factor of 0.38 mW m−1 K−2 at 307 K for n-type samples. They were 217 μV K−1 and 0.23 mW m−1 K−2, respectively, at 320 K for p-type samples. The electronic structures of impurity-doped Ba2AgSi3 were also discussed using first-principles calculations to investigate the insertion site of impurity atoms. The calculations suggest that the substitution of B (P) at any Si site shifts the Fermi level and transforms it into p-type (n-type) semiconductors. On the other hand, substitution of Ba or Ag sites with B or P is unlikely to occur in terms of formation energy.

Development of an Automated Hall Effect Experimentation Method for the Electrical Characterization of Thin Films

There has been drastic growth in the microelectronics industry in the recent past. The performance of these materials is influenced by their structural, electrical, and optical properties among others, depending on their applications. Therefore, the need to conduct measurements of the semiconductor characteristics precisely, quickly, and conveniently cannot be overstated. Some of the desirable features of measurements include usability, accuracy, resolution, repeatability, and consistency which cannot be assured with manually operated systems. This study strived to design and interface an automated computer-aided four-point probe test equipment that characterizes materials to determine their electrical properties. A four-point probe head, an electromagnet, NI Keithley model 6220 Precision current source, model 7001 switch, model 2182A Nanovoltmeter, and model 7065 Hall Effect card instruments were interfaced with the NI LabVIEW program running in a computer through a GPIB hub to a PC USB for its full control. The four-probe head was utilized to probe the samples with a square symmetry that was adopted for the measurement of the semiconductor properties. Reliability tests were conducted on a standard P-type Germanium sample. The collected data was within 0.32% of the expected results. This work forms a basis for automating similar systems that were inherently designed to be operated manually. Keywords: Automated Hall Effect, manually operated systems, Hall angle, thin films, string manipulation routines.

Room temperature deposition of stable p-type ZnO:N thin films through chemical species modulation using reactive pulsed laser deposition

Low temperature processing as well as long-term electrical stability are required to match p-type ZnO thin films with flexible electronics applications. Herein, ZnO and ZnO:N thin films were deposited at room temperature by reactive pulsed laser deposition of a zinc metallic target. Several ZnO thin films were obtained by varying the oxygen working pressure from 1.2 × 10-5 Torr to 3.5 × 10-2 Torr. Chemical concentration was smoothly tuned as demonstrated by in situ X-ray Photoelectron Spectroscopy. Introducing and varying both N2 and O2 fluxes at a constant pressure, N-doped ZnO films from 0.3 at.% to 5 at.% were deposited. Adjusting the N2/O2 flux ratio, p-type ZnO:N films were successfully achieved, exhibiting a carrier concentration of 5.3 × 1018 cm−3, resistivity of 2 Ωcm, and mobility of 0.5 cm2V-1s−1. Four representative p-type samples were analyzed to confirm chemical and electrical reproducibility. Electrical properties of one of these films were measured again nine months after deposited, and p-type conductivity was still observed. Cathodoluminescence revealed green-dominant emissions in n-ZnO and UV-dominant emissions in p-ZnO:N films as nitrogen doping effect. Finally, a p-n diode was fabricated using photolithography, exhibiting rectification performance even nine months after deposited. P-type ZnO:N presented here are suitable for flexible electronics devices fabrication.

Mechanisms of Current Transition in High Compensated Silicon Samples with Zinc Nanoclusters

This article presents experimental results on the study of the current-voltage characteristics of strongly compensated n- and p-type silicon samples diffusion-doped with zinc at a temperature of 80 K. The current-voltage characteristics of the studied samples contain both sublinear and superlinear sections. Several (up to eight) characteristic areas were found, the number of which depends on the degree of illumination, temperature, and electrical resistivity of the sample. Under certain conditions, there is an alternation of sections of the current-voltage characteristic with negative differential conductivity of the N- and S-type, behind which current instabilities with an infra-low frequency are observed. The appearance of sections of the current-voltage characteristic with a quadratic dependence is explained by the presence of fast and slow recombination centers associated with zinc nanoclusters, and sublinear sections are explained in terms of the theory of the "injection depletion effect". The formation of nanoclusters with the participation of zinc ions was confirmed by atomic force microscopy studies.

An Automatic Apparatus for Simultaneous Measurement of Seebeck Coefficient and Electrical Resistivity

A fully automated experimental system was designed for simultaneous measurement of the Seebeck coefficient and electrical resistivity of thermoelectric materials in bulk form. The system incorporates a straightforward and easily fabricated sample holder along with commercially available electronic instrument components. The sample holder showcases a compact design that utilizes two Peltier module heaters to induce sample heating and generate the required temperature gradient. System automation and control are achieved through the implementation of a LabView program. The Seebeck voltage and resistance of the sample (under specified temperature conditions) are determined using I–V measurements. The Seebeck voltage and resistance of the sample correspond to the intercept and slope of the I–V characteristic diagram in the four-point probe method, respectively. To verify the accuracy and reliability of the developed apparatus, a variety of experiments were performed on N-type and P-type bismuth telluride samples. The measurement results closely matched those obtained from commercial systems, with an overall data difference of less than 10% for both the Seebeck coefficient and resistivity measurements.

Bias-voltage photoconductance and photoluminescence for the determination of silicon-dielectric interface properties in SiO2/Al2O3 stacks

This paper presents an advanced measurement method for controlling the surface charge carrier density of passivated silicon wafers during photoconductance and photoluminescence measurements, by employing semitransparent poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) electrodes with an applied bias voltage. This is employed to study and analyze charge carrier dynamics in dielectric layers by measuring their direct influence on effective lifetime. With this method, the carrier population at the surface and the effective carrier lifetimes of n- and p-type samples can be investigated, from which the fixed charge carrier density Qf of the passivation can be extracted. Additionally, the defect density Dit can also be derived from the minimum lifetime values at flatband voltage. In SiO2/Al2O3 stacks with varying SiO2 interlayer thickness, it was shown that by changing the SiO2 thickness, the carrier density Qf can be tuned to a wide range of values, which corresponds to the results obtained in other studies. An increase in interlayer thickness resulted in a decrease in Qf. Varying the SiO2 thickness, the behavior of the respective effective lifetime under bias voltage also changes, exhibiting hysteresis-like effects, which are attributed to additional charges getting trapped at the surface during bias-voltage application. This effect is much more pronounced for samples with a thinner SiO2 layer as well as for the n-type samples. Additionally, the doping type also influences the magnitude of Qf, with p-type samples generally reaching lower absolute values. It was also shown that aging of the samples had a significant effect on the measured Qf, which was increased compared to the initial Qf of the passivation. This effect was more pronounced for the n-type samples. The measurements were realized by a cost-effective and easy-to-use microcontroller-based potentiostat, which can be used as a simple add-on to existing photoconductance or photoluminescence measurement setups.

Inverting electrodeposited nanostructured Cu2O thin films from n-type to p-type semiconductors and variation of their physical and photoelectrochemical properties for optoelectronic applications

Employing identical techniques to produce the semiconductor with n and p-type conductivity is one of the most important keys to fabricating higher performance optoelectronic devices. Therefore, here the electrodeposition technique was employed to grow nanostructured Cu2O thin films with different pH values ranging from 3.5 to 13 from the same precursors before starting the deposition process. The morphological, structural, optical, electrical, and photoelectrochemical properties of fabricated Cu2O thin films were investigated employing SEM, EDX, XRD, Raman, UV–Vis, PL, Photocurrent, Mott-Schottky, and electrochemical impedance spectroscopy (EIS) measurements. XRD results showed the formation of Cu, Cu2O, and CuO phases with low pH values, while only Cu2O phase is obtained with higher pH. Raman measurements proven phonon modes of nanostructured Cu2O thin films. The morphology varies with different shapes such as spherical, pyramids, and prisms according to pH values. The optical absorption edge has appeared between 475 nm and 575 nm which indicates the formation of Cu2O and the calculated band gap varies from 2 to 2.44 eV. PL measurements indicate two dominant peaks related to inter-band transitions and defects including copper interstitials. Photocurrent measurements denoted that samples with lower pH from 6 to 7.6 are n-type semiconductors, while higher ones from 8 to 13 are p-type semiconductors. Mott-Schottky measurements showed that the donor’s density declines from about 2 × 1017 cm− 3 to about 1.6 × 1016 cm− 3 as pH increases from 6 to 7.6 whereas the acceptor’s density rises from about 1.25 × 1017 cm− 3 to about 3 × 1018 cm− 3 as pH increases from 8 to 13. EIS results show that both p-type and n-type samples have higher separation and transfer of charge carriers. Our outcomes indicate that the electrodeposited nanostructured Cu2O thin films are appropriate materials for biosensors, solar cells, and supercapacitors applications.

Excellent surface passivation of p-type TOPCon enabled by ozone-gas oxidation with a single-sided saturation current density of ∼ 4.5 fA/cm2

High-quality p-type tunnel oxide passivated contact (p-type TOPCon) is a feasible technical solution to further improve the efficiency of TOPCon silicon solar cells. Plasma-enhanced chemical vapor deposition (PECVD) technology route could deposit boron-doped amorphous silicon film in-situ and thus becomes one of the most promising industry routes to prepare the TOPCon structure. However, the passivation quality of p-type TOPCon by PECVD is not satisfactory till now. In this work, we develop the high-performance p-type TOPCon technology by integrating the ozone-gas oxidation to prepare the ultra-thin SiOx film, which shows excellent passivation and contact properties. The experimental results suggest that the double-sided p-type TOPCon passivated samples with p-type Si substrates receive a maximal implied open-circuit voltage (iVoc) of ∼ 734 mV together with a minimum single-sided saturation current density (J0,s) of ∼ 4.5 fA/cm2. Correspondingly, the contact resistivity is less than 5 mΩ·cm2, yielding a high selectivity S10 of 15.6, which is one of the best values for p-type TOPCon technology. As a result, the precursor cell manifests an excellent iVoc of 717 mV, and the p-type silicon solar cell with rear-sided p-type TOPCon passivating contact receives a high efficiency of 22.23%. Generally, this work provides a promising technology for preparing the high-quality p-type TOPCon passivating contact for industrial application.

Passive Gate-Tunable Kinetic Photovoltage along Semiconductor-Water Interfaces.

Moving boundaries of electrical double layer at solid-liquid interface enables unprecedented persistent energy conversion and provokes a kinetic photovoltaic effect by moving an illumination region along the semiconductor-water interface. Here, we report a transistor-inspired gate modulation of kinetic photovoltage by applying a bias at the semiconductor-water interface. The kinetic photovoltage of both p-type and n-type silicon samples can be facilely switched on/off, stemming from the electrical-field-modulated surface band bending. In contrast to the function of solid-state transistors relying on external sources, passive gate modulation of the kinetic photovoltage is achieved simply by introducing a counter electrode with materials of desired electrochemical potential. This architecture provides the ability to modulate the kinetic photovoltage over three orders of magnitude and opens up a new way for self-powered optoelectronic logic devices.

Characterization of light induced degradation in PECVD silicon nitride passivated Cz silicon wafers using spectroscopic techniques

In this work we investigate the chemical species involved in the light induced degradation of plasma enhanced chemical vapor deposited (PECVD) hydrogenated silicon nitride (SiNx:H) passivated p-type and n-type samples under normal outdoor ambient conditions. The electrical characterization measurements along with Fourier Transform Infrared (FTIR) and photoluminescence (PL) spectroscopic techniques were utilized in this study. Significant reduction in effective minority carrier lifetime values and band to band PL intensities were noticed for both p-type and n-type samples after outdoor light soaking. The apparent defect density increased from 3.39 × 10−3 µs−1 to 1.68 × 10−2 µs−1 and 3.42 × 10−4 µs−1 to 3.46 × 10−3 µs−1, respectively for p-type and n-type samples after light soaking of 111 h corresponding to cumulative solar insolation of 95.7 kWh/m2. The changes in FTIR absorbance intensities of chemical species such as SiNyHa, SiNzHb, SiHm, SiO2i and SiOn after light soaking confirmed the role of oxygen in addition to hydrogen in both p-type and n-type samples. Spectroscopic PL analysis further validated the decrease in concentration of silicon-oxygen species and reduction in effective lifetime for n-type samples. We demonstrate that the chemical species contributing to light induced bulk and surface degradation can be identified by FTIR and PL spectroscopic techniques. This work would be beneficial for understanding, modeling and mitigating the degradation mechanisms in Cz silicon wafers passivated using PECVD dielectric films.

Large-Scale Colloidal Synthesis of Chalcogenides for Thermoelectric Applications

A simple and effective preparation of solution-processed chalcogenide thermoelectric materials is described. First, PbTe, PbSe, and SnSe were prepared by gram-scale colloidal synthesis relying on the reaction between metal acetates and diphenyl dichalcogenides in hexadecylamine solvent. The resultant phase-pure chalcogenides consist of highly crystalline and defect-free particles with distinct cubic-, tetrapod-, and rod-like morphologies. The powdered PbTe, PbSe, and SnSe products were subjected to densification by spark plasma sintering (SPS), affording dense pellets of the respective chalcogenides. Scanning electron microscopy shows that the SPS-derived pellets exhibit fine nano-/micro-structures dictated by the original morphology of the key constituting particles, while the powder X-ray diffraction and electron microscopy analyses confirm that the SPS-derived pellets are phase-pure materials, preserving the structure of the colloidal synthesis products. The resultant solution-processed PbTe, PbSe, and SnSe exhibit low thermal conductivity, which might be due to the enhanced phonon scattering developed over fine microstructures. For undoped n-type PbTe and p-type SnSe samples, an expected moderate thermoelectric performance is achieved. In contrast, an outstanding figure-of-merit of 0.73 at 673 K was achieved for undoped n-type PbSe outperforming, the majority of the optimized PbSe-based thermoelectric materials. Overall, our findings facilitate the design of efficient solution-processed chalcogenide thermoelectrics.

Cyclic Voltammetry and Impedance Measurements of Graphene Oxide Thin Films Dip-Coated on n-Type and p-Type Silicon

Despite the increasing interest in graphene, a less studied aspect is the enhancement of silicon (Si) performances due to the interaction with graphene-based materials. In this study, cyclic voltammetry and electric impedance measurements are performed on graphene oxide (GO) dip-coated on n-type and p-type Si samples. The electrical properties of GO on n-type Si samples are dramatically enhanced: The conductivity and the photocurrent meaningfully increase in comparison to bare n-type Si. Such findings could be used in a wide variety of optoelectronic applications, improving GO future applicability in the Si semiconductor industry.

Synergistic Approach Toward a Reproducible High zT in n-Type and p-Type Superionic Thermoelectric Ag2Te.

Recently, superionic thermoelectrics have attracted enormous attention due to their ultralow thermal conductivity and high figure-of-merit (zT). However, their high zT is generally obtained deep inside the superionic phase, e.g., near 1000 K in Cu2X (X: chalcogen atom) family despite a relatively low superionic transition temperature of ∼400 K. At such high temperatures, the liquid-like flow of the metal ions results in material's degradation. Here, we present thermoelectric properties of superionic Ag2Te synthesized by various methods. The sintered Ag2Te samples are shown to exhibit an unpredictable behavior with respect to the sign of thermopower (S) in the superionic phase and the magnitude of electrical conductivity (σ). We overcome this issue using an all-room-temperature fabrication technique leading to an excellent reproducibility from one sample to another. To improve the zT of Ag2Te beyond the phonon-liquid electron-crystal limit (∼0.64 at 575 K in the ingot samples), we adopted a heirarchical nanostructuring technique, which effectively suppressed the thermal conductivity, leading to a significant improvement in the zT values for both n-type and p-type samples. We obtained zT of 1.2 in the n-type and 0.64 in the p-type Ag2Te at 570 K. These values supersede the zT of any Ag2Te previously reported. At 570 K, for our ball-milled/cold-pressed samples, the critical current density for metal-ion migration exceeds 15 A cm-2, which further confirms that Ag2Te is a promising thermoelectric material. Our results are supported by first-principles density functional theory calculations of the electronic and thermal properties.

Enhanced thermoelectric performance of 3D-printed Bi2Te3-based materials via adding Te/Se

Bi2Te3-based materials were prepared by direct ink writing (DIW) 3D printing and their microstructure and thermoelectric properties were investigated with an emphasis on the effect of the content of DMF and Te/Se addition. As the mass ratio of DMF in the composition increased from 6.5% to 8.0% (in mass), the electrical conductivity deteriorated because of the corresponding increased porosity and organic remains in the samples. However, the volatilization of DMF would reduce the fluidity of the slurry. Thus, thermoelectric slurry with 7.0% DMF is the most suitable mass ratio for 3D printing. Additionally, adding Te in the p-type Bi0.4Sb1.6Te3 and adding Se in the n-type Bi2Te2.6Se0.4 have significantly improved their electrical conductivity due to the increased carrier concentration and mobility. Combining with the moderate Seebeck coefficient (∼200 μV/K), high power factors with ∼802 μW·m−1·K−2 and 1266 μW·m−1·K−2 were obtained for the n-type Bi2Te2.6Se0.4+10%Se and p-type Bi0.4Sb1.6Te3+7%Te, respectively, which result in the final relatively high zT values of 0.68 at 573 K and 0.56 at 330 K for n-type and p-type 3D-printed samples.