Temperature Dependent Hall Effect Research Articles

Doping properties of cadmium-rich arsenic-doped CdTe single crystals: Evidence of metastable AX behavior

Cd-rich composition and group-V element doping are of interest for simultaneously maximizing the hole concentration and minority carrier lifetime in CdTe, but the critical details concerning point defects are not yet fully established. Herein, we report on the properties of arsenic doped CdTe single crystals grown from Cd solvent by the travelling heater method. The photoluminescence spectra and activation energy of 74 ± 2 meV derived from the temperature-dependent Hall effect are consistent with AsTe as the dominant acceptor. Doping in the 1016 to 1017/cm3 range is achieved for measured As concentrations between 1016 and 1020/cm3 with the highest doping efficiency of 40% occurring near 1017 As/cm3. We observe persistent photoconductivity, a hallmark of light-induced metastable configuration changes consistent with AX behavior. Additionally, quenching experiments reveal at least two mechanisms of increased p-type doping in the dark, one decaying over 2–3 weeks and the other persisting for at least 2 months. These results provide essential insights for the application of As-doped CdTe in thin film solar cells.

Studies on the InAlN/InGaN/InAlN/InGaN double channel heterostructures with low sheet resistance

High quality InAlN/InGaN/InAlN/InGaN double channel heterostructures were proposed and grown by metal organic chemical vapor deposition. Benefiting from the adoption of the pulsed growth method and Two-Step AlN interlayer, the material quality and interface characteristics of the double channel heterostructures are satisfactory. The results of the temperature-dependent Hall effect measurement indicated that the transport properties of the double channel heterostructures were superior to those of the traditional single channel heterostructures in the whole test temperature range. Meanwhile, the sheet resistance of the double channel heterostructures reached 218.5 Ω/□ at 300 K, which is the record of InGaN-based heterostructures. The good transport properties of the InGaN double channel heterostructures are beneficial to improve the performance of the microwave power devices based on nitride semiconductors.

Incomplete Ionization of a 110\u2009meV Unintentional Donor in \u03b2-Ga2O3 and its Effect on Power Devices

Understanding the origin of unintentional doping in Ga2O3 is key to increasing breakdown voltages of Ga2O3 based power devices. Therefore, transport and capacitance spectroscopy studies have been performed to better understand the origin of unintentional doping in Ga2O3. Previously unobserved unintentional donors in commercially available (bar{2}01) Ga2O3 substrates have been electrically characterized via temperature dependent Hall effect measurements up to 1000 K and found to have a donor energy of 110 meV. The existence of the unintentional donor is confirmed by temperature dependent admittance spectroscopy, with an activation energy of 131 meV determined via that technique, in agreement with Hall effect measurements. With the concentration of this donor determined to be in the mid to high 1016 cm−3 range, elimination of this donor from the drift layer of Ga2O3 power electronics devices will be key to pushing the limits of device performance. Indeed, analytical assessment of the specific on-resistance (Ronsp) and breakdown voltage of Schottky diodes containing the 110 meV donor indicates that incomplete ionization increases Ronsp and decreases breakdown voltage as compared to Ga2O3 Schottky diodes containing only the shallow donor. The reduced performance due to incomplete ionization occurs in addition to the usual tradeoff between Ronsp and breakdown voltage.

Anomalous Hall effect in ion-beam sputtered Co2FeAl full Heusler alloy thin films

Investigations of temperature dependent anomalous Hall effect and longitudinal resistivity in Co2FeAl (CFA) thin films grown on Si(100) at different substrate temperature Ts are reported. The scaling of the anomalous Hall conductivity (AHC) and the associated phenomenological mechanisms (intrinsic and extrinsic) are analyzed vis-à-vis influence of Ts. The intrinsic contribution to AHC is found to be dominating over the extrinsic one. The appearance of a resistivity minimum at low temperature necessitates the inclusion of quantum corrections on account of weak localization and electron-electron scattering effects whose strength reduces with increase in Ts. The study establishes that the optimization of Ts plays an important role in the improvement of atomic ordering which indicates the higher strength of spin-orbit coupling and leads to the dominant intrinsic contribution to AHC in these CFA full Heusler alloy thin films.

Gold-Hyperdoped Black Silicon With High IR Absorption by Femtosecond Laser Irradiation

Gold (Au)-doped-textured silicon (Si) material with a thermostable absorption below bandgap (>50%) is obtained by femtosecond laser irradiation. Although the concentration of Au impurity (1019 cm−3 ) in textured Si is at least four orders of magnitude greater than the solid solubility of Au in crystalline Si, the sheet carrier density (approximately 1010 cm−2) in Au-doped Si is very low due to a self-compensation effect of Au impurity in Si material. The infrared absorption of Au-doped Si is related to laser-induced-structural defects and sub-band absorption of deep energy levels of Au in Si, which is determined by temperature-dependent Hall Effect measurement. Besides supersaturated doping of Au, a gold silicide phase is formed at textured Si surface.

Rubrene Single-Crystal Transistors with Perfluoropolyether Liquid Dielectric: Exploiting Free Dipoles to Induce Charge Carriers at Organic Surfaces

We report the use of perfluoropolyether (PFPE) as a liquid dielectric for use in rubrene single-crystal transistors. In particular, we explore the effect of the free, permanent dipoles in PFPE on the charge carrier accumulation and transport at the rubrene/PFPE interface. This provides a complementary approach to ionic liquid dielectrics where charge accumulation is achieved via mobile ions. Large hysteresis (i.e., a memory effect) in transistor transfer curves and peaks in the gate displacement current curves are observed and interpreted in terms of the dipolar response of PFPE to the gate electric field. The orientation of free dipoles in PFPE is found to have a significant influence on the formation and annihilation of the rubrene conducting channel. Hole densities on the order of 1011 cm–2 are achieved at the surface of rubrene, and a transition from band-like to hopping transport near the freezing point of PFPE is evidenced by temperature-dependent Hall effect and resistance measurements. Overall, th...

High Temperature Electronic and Thermal Transport Properties of EuGa2−x In x Sb2

The Zintl phase EuGa_2Sb_2 was synthesized via ball milling followed by hot pressing. The crystal structure of EuGa_2Sb_2 is comprised of a 3-D network of polyanionic [Ga_2Sb_2]^(2−) tunnels filled with Eu cations that provide charge balance (Eu^(2+)[Ga_2Sb_2]^(2−)). Here we report the temperature-dependent resistivity, Hall Effect, Seebeck coefficient and thermal conductivity for EuGa_(2−x)In_xSb_2 (x = 0, 0.05, 0.1) from 300 K to 775 K. Experimental results demonstrate that the material is a p-type semiconductor. However, a small band gap (∼0.1 eV) prevents EuGa_2Sb_2 from having high zT at higher temperatures. Isoelectronic substitution of In on the Ga site leads to point defect scattering of holes and phonons, thus reducing thermal conductivity and resulting in a slight improvement in zT.

Electrical properties of bilayer graphene synthesized using surface wave microwave plasma techniques at low temperature

Bilayer graphene was synthesized at low temperature using surface wave microwave plasma techniques where poly(methyl metacrylate) (PMMA) and methane (CH4) were used as carbon sources. Temperature-dependent Hall effect measurements were carried out in a helium atmosphere. Sheet resistance, sheet carrier density and mobility showed weak temperature dependence for graphene from PMMA, and the highest carrier mobility is 740 cm2 V−1 s−1. For graphene from CH4, tunneling of the domain boundary limited carrier transport. The difference in average domain size was determined by Raman signal maps. In addition, residuals of PMMA were detected on graphene from PMMA. The low sheet resistances of graphene synthesized at a temperature of 280 °C using plasma techniques were explained by the PMMA related residuals rather than the domain sizes.

Optical and electrical properties of high-quality Ti2O3 epitaxial film grown on sapphire substrate

Epitaxial film of Ti2O3 with high crystalline quality was grown on Al2O3 substrate by pulsed laser deposition process using a powder-pressed TiO2 target in active O2 flow. X-ray diffraction clearly reveals the (0006) crystalline Ti2O3 orientation and its $$ (10\overline{1} 0)_{{{\text{Ti}}_{ 2} {\text{O}}_{ 3} }} ||(10\overline{1} 0)_{\text{sapphire}} $$ in-plane epitaxial relationship with the substrate. Scanning electron microscopy images show that the film grew uniformly on the substrate with a Volmer–Weber mode. High-resolution transmission electron microscopy and selected area electron diffraction further confirm the high crystalline quality of the film. Transmittance spectrum shows that the Ti2O3 film is highly transparent in 400–800 nm with the optical band gap estimated to be 3.53 eV by Tauc plot. The temperature-dependent Hall effect measurement indicates that the Ti2O3 film appears to be n-type semiconductor with carrier concentration, mobility, and resistivity showing typical temperature-dependent behavior. The donor ionization energy was estimated to be 83.6 meV by linear relationship of conductivity versus temperature.

Composite Zn1−xCdxGeAs2 semiconductors: structural and electrical properties

We present the studies of structural, transport and magnetotransport properties of CdxGeAs2 crystals with the chemical content changing from 0 to 1. The structural studies indicate that this alloy exists as a composite two-phase material in almost the entire range of average chemical compositions. The two phase nature of our samples does have a significant influence on the carrier transport and magnetotransport of the composite alloy. The change of the conductivity type is observed at room temperature, from p-type for to n-type for x > 0.18, respectively. The Hall carrier mobility measured at room temperature decreases as a function of x from about 35 cm2 (V · s)−1 for the sample with x = 0 down to 3 cm2 (V · s)−1 for the sample with x = 0.233. For x > 0.233 the Hall carrier mobility shows an increase with x, up to the highest value around 875 cm2 (V · s)−1 observed for the sample with x = 1. Temperature dependent resistivity measurements indicate the presence of thermal activation of carriers with activation energy, Ea, with values from 20 to 30 meV for all the studied samples. The temperature dependent Hall effect data show that the grain boundary limited transport is strong in all our samples. For the samples with the negative MR is observed at temperatures lower than 100 K and at low magnetic field values, T. This effect is interpreted as a weak localization phenomenon with low values of phase coherence length, nm.

Effect of Strontium Incorporation on the p-Type Conductivity of Cu2O Thin Films Deposited by Metal–Organic Chemical Vapor Deposition

Temperature-dependent Hall effect and resistivity measurements are performed on polycrystalline Cu2O:Sr thin films deposited on glass substrate by metal organic-chemical vapor deposition. Their electrical properties are studied as a function of the strontium content, as determined by wavelength dispersive X-ray spectrometry. These electrical transport measurements highlight a copper vacancy doping mechanism induced by strontium incorporation, leading to a large decrease of the resistivity as low as 1.2 Ω·cm and corresponding free carrier mobilities about 15 cm2·V–1·s–1 at room temperature. Moreover, in addition to the main copper vacancy acceptor level, found at EA1 = 278 ± 21 meV above the top of the valence band, a coexisting shallower acceptor level with an ionization energy of EA2 = 133 ± 15 meV occurs for a strontium content above 5% and is tentatively assigned to a large size impurity–vacancy complex.

Structural and Magnetic Properties of Sputter-Deposited Mn–Fe–Ga Thin Films

We investigated structural, magnetic and electrical properties of sputter deposited Mn-Fe-Ga compounds. The crystallinity of the Mn-Fe-Ga thin films was confirmed using x-ray diffraction. X-ray reflection and atomic force microscopy measurements were utilized to investigate the surface properties, roughness, thickness and density of the deposited Mn-Fe-Ga. Depending on the stoichiometry, as well as the used substrates (SrTiO3 (001) and MgO (001)) or buffer layer (TiN) the Mn-Fe-Ga crystallizes in the cubic or the tetragonally distorted phase. Anomalous Hall effect and alternating gradient magnetometry measurements confirmed strong perpendicular magnetocrystalline anisotropy. Low saturation magnetization and hard magnetic behavior was reached by tuning the composition. Temperature dependent anomalous Hall effect measurements in a closed cycle He-cryostat showed a slight increase in coercivity with decreasing temperature (300K to 2K). TiN buffered Mn2.7Fe0.3Ga revealed sharper switching of the magnetization compared to the unbuffered layers.

Understanding and Control of Bipolar Self-Doping in Copper Nitride.

Semiconductor materials that can be doped both n-type and p-type are desirable for diode-based applications and transistor technology. Copper nitride (Cu3N) is a metastable semiconductor with a solar-relevant bandgap that has been reported to exhibit bipolar doping behavior. However, deeper understanding and better control of the mechanism behind this behavior in Cu3N is currently lacking in the literature. In this work, we use combinatorial growth with a temperature gradient to demonstrate both conduction types of phase-pure, sputter-deposited Cu3N thin films. Room temperature Hall effect and Seebeck effect measurements show n-type Cu3N with an electron density of 1017 cm-3 for low growth temperature (≈ 35 °C) and p-type with a hole density between 1015 cm-3 and 1016 cm-3 for elevated growth temperatures (50 °C to 120 °C). Mobility for both types of Cu3N was ≈ 0.1 cm2/Vs to 1 cm2/V. Additionally, temperature-dependent Hall effect measurements indicate that ionized defects are an important scattering mechanism in p-type films. By combining X-ray absorption spectroscopy and first-principles defect theory, we determined that VCu defects form preferentially in p-type Cu3N while Cui defects form preferentially in n-type Cu3N; suggesting that Cu3N is a compensated semiconductor with conductivity type resulting from a balance between donor and acceptor defects. Based on these theoretical and experimental results, we propose a kinetic defect formation mechanism for bipolar doping in Cu3N, that is also supported by positron annihilation experiments. Overall, the results of this work highlight the importance of kinetic processes in the defect physics of metastable materials, and provide a framework that can be applied when considering the properties of such materials in general.

Influence of dopant species and concentration on grain boundary scattering in degenerately doped In2O3 thin films

The influence of dopant species and concentration on the grain boundary scattering of differently doped In2O3 thin films is studied by means of room temperature and temperature dependent Hall effect measurements. Barrier heights at grain boundaries EB are evaluated from temperature dependent carrier mobility taking the theoretically calculated temperature dependence of intragrain mobility into account. It is thereby shown that also samples with a negative temperature coefficient of mobility exhibit significant grain boundary barrier heights and that EB is usually underestimated when evaluated based on Seto's model. It is also shown that the most commonly used Sn doping of In2O3 with a dopant concentration >2wt.% SnO2 leads to significantly enhanced grain boundary scattering compared to nominally undoped, Zr-doped and H-doped films. An effect of grain boundary scattering is even observed for carrier concentrations ~1021cm−3 if the films exhibit a pronounced (100) texture. The poor grain boundary properties of highly Sn-doped In2O3 are attributed to segregation of the Sn dopants, which is also indicated by measurements of surface Sn concentration.

Electrical properties of n-type GaSb substrates and p-type GaSb buffer layers for InAs/InGaSb superlattice infrared detectors

Lightly doped n-type GaSb substrates with p-type GaSb buffer layers are the preferred templates for growth of InAs/InGaSb superlattices used in infrared detector applications because of relatively high infrared transmission and a close lattice match to the superlattices. We report here temperature dependent resistivity and Hall effect measurements of bare substrates and substrate-p-type buffer layer structures grown by molecular beam epitaxy. Multicarrier analysis of the resistivity and Hall coefficient data demonstrate that high temperature transport in the substrates is due to conduction in both the high mobility zone center Γ band and the low mobility off-center L band. High overall mobility values indicate the absence of close compensation and that improved infrared and transport properties were achieved by a reduction in intrinsic acceptor concentration. Standard transport measurements of the undoped buffer layers show p-type conduction up to 300 K indicating electrical isolation of the buffer layer from the lightly n-type GaSb substrate. However, the highest temperature data indicate the early stages of the expected p to n type conversion which leads to apparent anomalously high carrier concentrations and lower than expected mobilities. Data at 77 K indicate very high quality buffer layers.

Temperature-dependent Hall effect measurements on Cz-grown silicon pulled from compensated and recycled feedstock materials

In this work, temperature-dependent Hall effect measurements in the temperature range 88–350K were carried out to investigate the electrical properties of three solar grade p-type Czochralski (Cz) silicon ingots, pulled from recycled p-type multi-crystalline silicon top cuts and compensated solar grade (SoG) feedstock. Material bulk properties including Hall mobility, carrier density and resistivity as functions of temperature were studied to evaluate the influence of compensation and impurities.Recycled top cut replacing poly-silicon as feedstock leads to a more uniform resistivity. In addition, higher concentrations of O and C, give rise to oxygen related defects, which act as neutral scattering centers displaying only a slight influence on the electrical properties at low temperature compared to the dominant compensation effect.The electrical performances of all samples are shown to be strongly dependent on compensation level, especially at the lowest temperature (~88K). A significant presence of incompletely ionized phosphorus was deduced through the measured carrier density. The temperature-dependent Hall effect measurements fit Klaassen׳s mobility model very well at low temperatures (<150K), showing consistency with the explanation of a reduced screening effect on ionized dopants for lightly doped silicon, while the deviation at the high temperature probably may be accounted for by the presence of as-grown defects, such as oxygen related defects and phosphorus clusters, which are usually neglected in most mobility models.

Comparative evaluation of InAs/GaSb superlattices for mid infrared detection: p–i–n versus residual doping

We report on the opto-electronic characterization of an InAs/GaSb superlattice (SL) midwave infrared p–i–n photodetector structure (pin-SL) in comparison with the same structure with no intentional doping (i-SL). Both structures were grown on an n-GaSb substrate using molecular beam epitaxy. The nominally undoped structure (i-SL) presented p–i–n like behavior and showed a photovoltaic mode photoresponse due to the residual doping and native defects in this material system. For ∼77 K operation, 0.76 and 0.11 A W–1 responsivity values were obtained at 4 μm from the pin-SL and i-SL structures, respectively. Activation energy analysis showed that the recombination current was dominant in both structures but different recombination centers were involved. The same i-SL structure was also grown on a semi-insulating (SI)-GaAs substrate to study the contribution of the substrate to the carrier density in the SL layers. Temperature dependent Hall effect measurements showed that the nominally undoped structure presented both n-type and p-type conductivities; however, the temperature at which the carrier type switched polarity was observed to be at higher values when the i-SL structure was grown on the SI-GaAs substrate. In addition, a higher carrier density was observed for i-SL on the GaSb substrate than on the GaAs substrate.

Limits of carrier mobility in Sb-doped SnO2conducting films deposited by reactive sputtering

Electron transport in Sb-doped SnO2 (ATO) films is studied to unveil the limited carrier mobility observed in sputtered films as compared to other deposition methods. Transparent and conductive ATO layers are deposited from metallic tin targets alloyed with antimony in oxygen atmosphere optimized for reactive sputtering. The carrier mobility decreases from 24 cm2 V−1 s−1 to 6 cm2 V−1 s−1 when increasing the doping level from 0 to 7 at. %, and the lowest resistivity of 1.8 × 10−3 Ω cm corresponding to the mobility of 12 cm2 V−1 s−1 which is obtained for the 3 at. % Sb-doped ATO. Temperature-dependent Hall effect measurements and near-infrared reflectance measurements reveal that the carrier mobility in sputtered ATO is limited by ingrain scattering. In contrast, the mobility of unintentionally doped SnO2 films is determined mostly by the grain boundary scattering. Both limitations should arise from the sputtering process itself, which suffers from the high-energy-ion bombardment and yields polycrystalline ...

Synthesis of Cu2O from CuO thin films: Optical and electrical properties

Hole conducting, optically transparent Cu2O thin films on glass substrates have been synthesized by vacuum annealing (5×10−6 mbar at 700 K for 1 hour) of magnetron sputtered (at 300 K) CuO thin films. The Cu2O thin films are p-type and show enhanced properties: grain size (54.7 nm), optical transmission 72% (at 600 nm) and Hall mobility 51 cm2/Vs. The bulk and surface Valence band spectra of Cu2O and CuO thin films are studied by temperature dependent Hall effect and Ultra violet photo electron Spectroscopy (UPS). CuO thin films show a significant band bending downwards (due to higher hole concentration) than Cu2O thin films.

Structural characterization and anomalous Hall effect of Rh2MnGe thin films

We present the preparation, structural investigations, and transport properties of L2 1 -ordered epitaxial Rh 2 MnGe Heusler thin films grown by pulsed laser deposition . The films grow (1 0 0) oriented on (1 0 0)MgO substrate with [ 0 1 1 ] Rh 2 MnGe ∥ [ 0 1 0 ] MgO . The rocking curve widths of (4 0 0) reflections are below 1° and decrease with increasing deposition temperature. The flat surface of the thin films allowed lithographic patterning enabling quantitative magnetotransport measurements. We measured resistivity and the Hall effect . We suggest skew scattering as the dominant effect in the temperature dependent anomalous Hall effect, consistent with the theoretically expected skew scattering in the superclean limit. Our findings are in agreement with previously reported small orbital moments in Rh 2 MnGe bulk material probed by magnetic x-ray absorption spectroscopy measurements. • Epitaxial Rh 2 MnGe films were grown by pulsed laser deposition. • The films were structurally investigated by XRD and RHEED. • The AHE of Rh 2 MnGe increases with temperatures from 5 to 290 K. • The spin–orbit coupling is similar to other Heusler thin films in spite of heavy Rh atoms.