Temperature-dependent Hall Effect Measurements Research Articles

Hall effect analysis of boron and nitrogen background concentration in undoped CVD diamond

Pure single crystal diamond is a superior material for electronic, quantum, and detection applications. The state-of-the-art level of background concentrations of boron and nitrogen in such diamonds is about 1 ppb, which is quite close to the detection limit of the best chemical analysis techniques. In this work, we show that the boron concentration of ∼0.1 ppb causes conductivity of ∼5 kΩ cm of the single crystal diamond if the nitrogen concentration is lower. In such a case, the temperature dependent Hall effect measurement provides ∼100 times better detection limit for the concentration of the impurities in diamond compared to the conventional optical techniques. As a result, we have found the background concentrations of boron and nitrogen at the level of 0.07 and 0.02 ppb, respectively. This fact leads to a conclusion that growth of the insulating diamond is possible only when the nitrogen concentration is higher than the boron concentration.

Temperature-driven spin reorientation transition in van der Waals Cr1.7Te2 ferromagnet

The phenomenon of spin reorientation transition in magnetic materials is truly captivating, as it involves a fascinating change in the direction of magnetic moments. However, the research on spin reorientation transition in two-dimensional (2D) magnetic materials has received limited attention, thus hindering its immense potential for significant advancements in various device applications. In this study, we present a discovery of a spin reorientation transition from an in-plane to an out-of-plane direction in the van der Waals ferromagnet Cr1.7Te2 (Tc = 300 K). This transition occurs at 70 K when the temperature ranges from 3 to 300 K, which is evidenced by the temperature-dependent Hall effect and magnetic anisotropy energy measurements. Notably, the anisotropic evolution observed reveals that the shape anisotropy effect surpasses the magnetocrystalline anisotropy in van der Waals ferromagnet at low temperatures, which is distinct from reported ferromagnetic materials. Furthermore, temperature-dependent x-ray diffraction characterizations confirm that no structural phase transition occurs during this intriguing spin reorientation transition process. These findings establish a strong and solid foundation, offering a promising platform for the design and development of cutting-edge 2D spintronic devices.

Single crystal growth and transport properties of narrow-bandgap semiconductor RhP2

Abstract Here, we report the growth of high-quality single crystals of RhP2, and systematically study its structure and physical properties by transport, magnetism, and heat capacity measurements. Single-crystal X-ray diffraction revealed RhP2 adopts a monoclinic structure with the cell parameters a=5.7347(10) Å, b=5.7804(11) Å, and c=5.8222(11) Å, space group P21/c (No. 14). The electrical resistivity ρ(T) measurements indicate that RhP2 exhibits a narrow band gap behavior with the activation energies of 223.1 m eV and 27.4 m eV for two distinct regions, respectively. The temperature-dependent Hall effect measurements show electron domain transport behavior with a low charge carrier concentration. We found that RhP2 has a high mobility μe~210 cm2v-1s-1 with carrier concentrations ne~3.3×1018 cm-3 at 300 K with a narrow band gap feature. The high mobility μe reached a maximum of approximately 340 cm2v-1s-1 with carrier concentrations ne~2×1018 cm-3 at 100 K. No magnetic phase transitions were observed from the susceptibility χ(T) and specific heat Cp(T) measurements of RhP2. Our results not only offer effective potential as a material platform for studying exotic physical properties and electron band structures but also motivate further exploration of their potential photovoltaic and optoelectronic applications.

Investigation of photosensitive and photodetector characteristics of n-TPA-IFA/p-Si heterojunction structure

n-TPA-IFA organic material was synthesized and deposited on p-Si by spin coating method to produce n-TPA-IFA/p-Si heterojunction diode. We determined that the dielectric constant and energy band gap of TPA-IFA organic material were 3.91 and 3.37 eV by DFT/B3LYP/6-311G(d,p) method using on Gaussian 09 W, respectively, and the carrier type of TPA-IFA organic semiconductor material was also n-type at room temperature from temperature-dependent hall effect measurements. Using forward and reverse bias I–V measurements in the dark and under various light intensities, we examined the key electrical characteristics of the n-TPA-IFA/p-Si heterojunction diode, including Φb\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\Phi }_{b}$$\\end{document} and n\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$n$$\\end{document}. It was determined that the rectification ratio (RR) was approximately 104. The reverse current's observed increasing behavior with increasing light indicates that the produced heterojunction diode can be utilized as a photodiode, detector, or sensor. The values of n, Φb\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\Phi }_{b}$$\\end{document}, and Io were determined using I–V data in dark as 1.34, 0.91 eV, and 7.25 9 10–12 A, respectively. On the other hand, when the n-TPA-IFA/p-Si heterojunction diode is exposed to 100 mW/cm2 illumination, these parameters were obtained as 1.85, 0.80 eV, and 5.11 9 10–10 A, respectively. Photovoltaic parameters such as short circuit current (Isc) and open circuit voltage (Voc) were determined as 0.018 mV, 0.08 A and 0.050 mV, 0.29 A under 20 mW/cm2 light and 100 mW/cm2 light intensity, respectively. The photodetector properties of n-TPA-IFA/p-Si heterostructure were explored at different light intensities, and the photoresponsivity (R), photosensitivity (PS), specific detectivity (D∗\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${D}^{*}$$\\end{document}), and linear dynamic range (LDR) of the heterojunction changed with reverse voltage and light intensity. It was found that as light intensity increased, the linear dynamic range (LDR), a crucial characteristic for image sensors, increased as well (10.15 dB and 18.84 dB for 20 and 100 mW/cm2).

Formation of Grown-In Nitrogen Vacancies and Interstitials in Highly Mg-Doped Ammonothermal GaN.

The formation of intrinsic point defects in the N-sublattice of semi-insulating Mg-doped GaN crystals grown by the ammonothermal method (SI AT GaN:Mg) was investigated for the first time. The grown-in defects produced by the displacement of nitrogen atoms were experimentally observed as deep traps revealed by the Laplace transform photoinduced transient spectroscopy in the compensated p-type crystals with the Mg concentrations of 6 × 1018 and 2 × 1019 cm-3 and resistivities of ~1011 Ωcm and ~106 Ωcm, respectively. In both kinds of materials, three closely located traps with activation energies of 430, 450, and 460 meV were revealed. The traps, whose concentrations in the stronger-doped material were found to be significantly higher, are assigned to the (3+/+) and (2+/+) transition levels of nitrogen vacancies as well as to the (2+/+) level of nitrogen split interstitials, respectively. In the material with the lower Mg concentration, a middle-gap trap with the activation energy of 1870 meV was found to be predominant. The results are confirmed and quantitatively described by temperature-dependent Hall effect measurements. The mechanism of nitrogen atom displacement due to the local strain field arising in SI AT GaN:Mg is proposed and the effect of the Mg concentration on the charge compensation is discussed.

Record high electron mobilities in high-purity GaN by eliminating C-induced mobility collapse

Impact of carbon impurities on the electrical properties of lightly doped n-type GaN [electron concentration ∼(1–2)×1015 cm−3 at room temperature] was investigated using temperature-dependent Hall effect measurements. GaN crystals with a threading dislocation density of (1–3)×106 cm−2 were grown by our originally developed quartz-free hydride vapor phase epitaxy method, which enabled the background Si, O, and C concentrations to be suppressed to below the mid-1014 cm−3 range. We prepared three samples with different C concentrations ([C]) by intentional C doping. The C incorporation induced severe mobility collapse at temperatures greater than 60 K, where the measured mobility decreased and deviated from the theoretical value as [C] increased. The mobility collapse was eliminated for the purest GaN crystal with [C] ∼1.4×1014 cm−3, exhibiting a record high room-temperature mobility of 1480 cm2/(V·s), as well as a record high maximum mobility of 14 300 cm2/(V·s) at 62 K. The latter was almost double the previous record. We found that the overall mobility behavior can be well reproduced by adding an empirical [C]-dependent mobility component expressed as μUNK=K/TnUNK with 1≤nUNK≤2 and K∝C−1 to the conventional mobility theory (phonon and impurity scattering). Although the mechanism of the component remains uncertain, our findings provide insight into the unsolved issue of mobility collapse.

Grain boundary passivation in cuprous oxide thin films via nitrogen annealing

In this work, polycrystalline cuprous oxide (Cu2O) films deposited by magnetron sputtering were annealed in situ in N2 atmospheres. Room-temperature and temperature-dependent Hall-effect measurements were performed on as-deposited and N2-annealed Cu2O films to probe the electrical transport mechanisms. The results show that the hole mobility of 0.8 Pa N2-annealed Cu2O film is enhanced compared with its as-deposited counterpart. It is shown that at low temperatures, the hole mobilities of Cu2O films appear to be limited by grain boundary scattering, while acoustic-phonon scattering comes into play at elevated temperatures. Moreover, the grain boundary potential barrier height which inhibits the hole transport is found to be reduced by N2-annealing at 0.8 Pa, thereby leading to the observed improvement in the hole mobility. It is thought that N2 is mainly concentrated at the grain boundaries in polycrystalline Cu2O films, thus passivating the grain boundary defect trap states. The results reported in this work suggest that N2-annealing induced grain boundary passivation could be an effective method to improve the photoelectric properties of polycrystalline Cu2O films.

Evaluation of electrical properties in anodized n-GaN grown on sapphire substrates at different anodization voltages

n-GaN grown on sapphire substrates was anodized in an electrolyte solution at different voltages (2 and 4 V) for 3600 s, and the electrical properties of the anodized n-GaN were evaluated. The resistivity of the sample anodized at 2 V increased by a factor of 2.4 at RT, and that of the sample anodized at 4 V increased by a factor of 76 at RT The analysis of temperature dependent Hall effect measurements revealed that anodization changes original donor levels and/or generates energy levels depending on anodization voltages. Anodization has a possibility to transform GaN into GaON-like materials.

Creating zinc-hyperdoped silicon with modulated conduction type by femtosecond laser irradiation

Silicon, as the earth-abundant semiconductor, has low cost and good compatibility with mature complementary metal-oxide-semiconductor technology. Therefore, instead of choosing the proper semiconductor with a specific bandgap energy, hyperdoping technique, which can introduce deep-level dopants and intermediate band into silicon, enable silicon to operate in infrared wavebands. Particularly, the hyperdoped silicon with transition metals, having low ionized impurity scatting, makes silicon a promising infrared detection material. In present work, zinc-hyperdoped silicon is fabricated by femtosecond pulsed laser irradiation. The doping concentration of zinc has exceeded 1019 cm−3, and even reached 1022 cm−3, which is about five orders of magnitude greater than the solid solubility of zinc in crystalline Si. The zinc-hyperdoped silicon shows sub-bandgap absorptance of 87.86 % at 1310 nm. Temperature-dependent Hall effect measurements prove that zinc doping results in acceptor energy level located at 0.520 eV above the valence band maximum. It is worth nothing that, zinc-oxygen related defect state results in donor energy level located at 0.252 eV below the conduction band minimum when lower laser fluence is used, which means the energy level of impurity is altered by the presence of undesignedly doped oxygen atoms, suggesting compound formation between the zinc atoms and oxygen atoms.

Preparation of degenerate n-type AlxGa1−xN (0 < x ≤ 0.81) with record low resistivity by pulsed sputtering deposition

Highly conductive AlGaN alloys hold a great technological potential, wherein the degenerate n-type doping is key in reducing parasitic resistances in electronic and opto-electronic devices. Nonetheless, AlxGa1−xN elaborated in conventional methods exhibits degraded electron concentration at high Al compositions. Here, we demonstrated the growth of degenerate n-type AlxGa1−xN (0 < x ≤ 0.81) with record high electron concentrations by using the pulsed sputtering deposition (PSD) method. The fabricated samples were investigated by cathodoluminescence and Hall-effect measurements in studying the related deep-level emission and electron mobility, respectively. Our findings showed that the PSD-grown heavily Si-doped AlxGa1−xN exhibits record low resistivity values: 2.5 × 10−3 Ω cm with an electron concentration of 1.2 × 1020 cm−3 for x = 0.60 and 1.7 × 10−2 Ω cm with an electron concentration of 3.2 × 1019 cm−3 for x = 0.81. Temperature-dependent Hall-effect measurements confirmed the degenerate nature of heavily Si-doped AlxGa1−xN up to x = 0.81. These results clearly show that the PSD n-type AlGaN is quite promising for reducing parasitic resistance in AlGaN based far UVC light-emitting devices and high breakdown voltage electron devices.

Growth of α-In2O3 films with different concentrations of In2O3 powder used as source precursor by mist chemical vapor deposition

The heteroepitaxial growth of In2O3 on a (0001) α-Al2O3 substrate was carried out using the mist chemical vapor deposition method. The concentrations of In2O3 powder in the source precursor solution varied between 0.025 and 0.250 mol l−1. An increase in the growth rate was observed with the increasing In2O3 powder concentration, and the highest growth rate of 4.2 μm h−1 was obtained at a powder concentration of 0.150 mol l−1. An improvement in the electrical properties was eventually observed, i.e. the lowest carrier concentration of 3.1 × 1017 cm−3 and the highest Hall mobility of 241 cm2 V−1 s−1 at room temperature were obtained at a powder concentration of 0.150 mol l−1. The temperature-dependent Hall effect measurement for the sample showed pronounced carrier freeze-out in a temperature range of 300–30 K, indicating that the α-In2O3 film had near-non-degenerate conductivity.

Silicon-doped β-Ga2O3 films grown at 1 µm/h by suboxide molecular-beam epitaxy

We report the use of suboxide molecular-beam epitaxy (S-MBE) to grow β-Ga2O3 at a growth rate of ∼1 µm/h with control of the silicon doping concentration from 5 × 1016 to 1019 cm−3. In S-MBE, pre-oxidized gallium in the form of a molecular beam that is 99.98% Ga2O, i.e., gallium suboxide, is supplied. Directly supplying Ga2O to the growth surface bypasses the rate-limiting first step of the two-step reaction mechanism involved in the growth of β-Ga2O3 by conventional MBE. As a result, a growth rate of ∼1 µm/h is readily achieved at a relatively low growth temperature (Tsub ≈ 525 °C), resulting in films with high structural perfection and smooth surfaces (rms roughness of <2 nm on ∼1 µm thick films). Silicon-containing oxide sources (SiO and SiO2) producing an SiO suboxide molecular beam are used to dope the β-Ga2O3 layers. Temperature-dependent Hall effect measurements on a 1 µm thick film with a mobile carrier concentration of 2.7 × 1017 cm−3 reveal a room-temperature mobility of 124 cm2 V−1 s−1 that increases to 627 cm2 V−1 s−1 at 76 K; the silicon dopants are found to exhibit an activation energy of 27 meV. We also demonstrate working metal–semiconductor field-effect transistors made from these silicon-doped β-Ga2O3 films grown by S-MBE at growth rates of ∼1 µm/h.

Doping of dilute nitride compounds grown by liquid phase epitaxy

The doping of dilute nitrides is an important point of the growth and processing technology for different optoelectronic devices based on these compounds. In this paper, both intentional and nonintentional doping of InGaAsN and GaAsSbN have been investigated by temperature-dependent Hall effect measurements. Dilute nitrides layers have been grown by low-temperature (Tcryst < 600 °C) liquid-phase epitaxy (LPE). The chemical elements Sn and Mg have been chosen as n-type and p-type dopants, respectively. All nominally undoped InGaAsN layers are n-type with free carrier concentration about one order of magnitude higher than layers not containing nitrogen and grown by LPE. This makes it difficult to obtain epitaxial layers with p-type conductivity with these compounds. However, high-quality n-type, p-type and nearly compensated GaAsSbN layers have been successfully grown covering a large range of carrier concentrations from 1015 to 6×1018 cm−3. The quality of the GaAsSbN layers has been evidenced by a good photoresponse with a low energy threshold extended down to 1.2 eV as obtained by surface photovoltage spectroscopy.

Growth and characterization of IR nonlinear optical PbIn6Te10 crystal

The crack-free PbIn6Te10 single crystal with ϕ28 mm × 90 mm was grown by the modified Vertical Bridgman method. Experimental results show that the main body of the boule is a PbIn6Te10 single crystal, while the tail has a certain amount of PbTe and Te. The measurements of UV and IR transmission demonstrate that the transmittance of PbIn6Te10 in 3.5–5.0 µm and 8–12 µm is more than 57 % and the corresponding absorption coefficient is in the range of 0.1–0.3 cm−1. The electrical properties of PbIn6Te10 crystal were studied within 50–300 K by temperature-dependent Hall-effect measurement. It is found that the as-grown crystal is an N-type semiconductor, and the carrier concentration varies nearly exponentially duo to the donor impurity ionization in the measured temperature range. Furthermore, the donor impurity ionization energy ∇ED was evaluated to be 0.04779 eV, and the fitted carrier mobility μH ∝ T−3/2 reveals the primary scattering mechanism within 170–300 K is the lattice vibration scattering.

Activation of implanted Si, Ge, and Sn donors in high-resistivity halide vapor phase epitaxial β-Ga2O3:N with high mobility

Activation of implanted donors into a highly-resistive, nitrogen-doped homoepitaxial β-Ga2O3 has been investigated. Nitrogen acceptors with the concentration of ∼1017 cm−3 were incorporated during epitaxial growth yielding low-doped (net donor concentration &amp;lt;1014 cm−3) films subsequently implanted with Si, Ge, and Sn. Upon Ohmic contact formation to the implanted regions, sheet resistance values of 314, 926, and 1676 Ω/sq were measured at room temperature for the Si-, Ge-, and Sn-implanted samples, respectively. Room temperature Hall measurements resulted in sheet carrier concentrations and Hall mobilities of 2.13 × 1014 /93, 8.58 × 1013/78, and 5.87 × 1013/63 cm2/(V s), respectively, for these three donor species. Secondary ion mass spectroscopy showed a volumetric dopant concentration of approximately 2 × 1019 cm−3 for the three species, resulting in carrier activation efficiencies of 64.7%, 40.3%, and 28.2% for Si, Ge, and Sn, respectively. Temperature-dependent Hall effect measurements ranging from 15 to 300 K showed a nearly constant carrier concentration in the Si-implanted sample, suggesting the formation of an impurity band indicative of degenerate doping. With a bulk carrier concentration of 1.3 × 1019 cm−3 for the Si implanted sample, a room temperature mobility of 93 cm2/(V s) is among the highest reported in Ga2O3 with a similar carrier concentration. The unimplanted Ga2O3:N regions remained highly resistive after the surrounding areas received implant and activation anneal. These results open the pathway for fabricating Ga2O3 devices through the selective n-type doping in highly resistive epitaxial Ga2O3.

Confinement of Electrons at the LaInO3/BaSnO3 Heterointerface

AbstractThe properties of the conductance at the LaInO3/BaSnO3 heterointerface are reported. The heterointerface is formed by covering the semi‐insulating BaSnO3:La thin films with 10 nm LaInO3 films, which are all epitaxially grown on NdScO3 substrates. Structural properties of BaSnO3 thin films are investigated by means of X‐ray diffraction and transmission electron microscopy and exhibit a threading dislocation density of 6 × 1010 cm−2. Via capacitance–voltage (C–V) measurements, clear evidence is present for the accumulation of electrons at the interface within 2.5 nm in the BaSnO3 layer, confirming the formation of a 2D electron gas (2DEG). Additionally, temperature dependent Hall effect measurements reveal a semiconducting behavior of the electron density of the 2DEGs. The room temperature mobility of 22 cm2 V−1 s−1 at an electron density of 4 × 1013 cm−2 is found to increase as the temperature decreases to 25 K.

Controlled Si doping of β -Ga2O3 by molecular beam epitaxy

We report controlled silicon doping of Ga2O3 grown in plasma-assisted molecular beam epitaxy. Adding an endplate to the Si effusion cell enables the control of the mobile carrier density, leading to over 5-orders of magnitude change in the electrical resistivity. Room temperature mobilities &amp;gt;100 cm2/V s are achieved, with a peak value &amp;gt;125 cm2/V s at a doping density of low-1017/cm3. Temperature-dependent Hall effect measurements exhibit carrier freeze out for samples doped below the Mott criterion. A mobility of 390 cm2/V s is observed at 97 K.

Low resistivity, p-type, N-Polar GaN achieved by chemical potential control

We report on low resistivity (1.1 Ω cm) in p-type bulk doping of N-polar GaN grown by metalorganic chemical vapor deposition. High nitrogen chemical potential growth, facilitated by high process supersaturation, was instrumental in reducing the incorporation of compensating oxygen as well as nitrogen-vacancy-related point defects. This was confirmed by photoluminescence studies and temperature-dependent Hall effect measurements. The suppressed compensation led to an order of magnitude improvement in p-type conductivity with the room-temperature hole concentration and mobility measuring 6 × 1017 cm−3 and 9 cm2 V−1 s−1, respectively. These results are paramount in the pathway towards N-polar GaN power and optoelectronic devices.

Tuning Phase Transition and Thermochromic Properties of Vanadium Dioxide Thin Films via Cobalt Doping.

Vanadium dioxide (VO2) featuring a distinct thermally triggered phase transition is regarded as the most attractive thermochromic material for smart window applications. However, the high transition temperature (∼67 °C) and moderate luminous transmittance (<50%) of the pristine VO2 circumvent room temperature applications. In this work, epitaxial cobalt-doped VO2 thin films were fabricated to tailor the electric and optical properties on a c-plane sapphire substrate. At the highest doping concentration of 10%, the transition temperature of VO2 is reduced to 44 °C, accompanied by a high luminous transmittance of 79% for single-element Co-doped VO2. The roles of cobalt doping and detailed band variation are fully explained experimentally and by modeling (DFT calculation), respectively. Furthermore, the dramatically increased carrier concentration in cobalt-doped VO2 underscores the promising future of cobalt-doped VO2 unveiled by temperature-dependent Hall effect measurement.

Plasmon-Phonon Coupling in Electrostatically Gated β-Ga2O3 Films with Mobility Exceeding 200 cm2 V-1 s-1.

Monoclinic β-Ga2O3, an ultra-wide bandgap semiconductor, has seen enormous activity in recent years. However, the fundamental study of the plasmon-phonon coupling that dictates electron transport properties has not been possible due to the difficulty in achieving higher carrier density (without introducing chemical disorder). Here, we report a highly reversible, electrostatic doping of β-Ga2O3 films with tunable carrier densities using ion-gel-gated electric double-layer transistor configuration. Combining temperature-dependent Hall effect measurements, transport modeling, and comprehensive mobility calculations using ab initio based electron-phonon scattering rates, we demonstrate an increase in the room-temperature mobility to 201 cm2 V-1 s-1 followed by a surprising decrease with an increasing carrier density due to the plasmon-phonon coupling. The modeling and experimental data further reveal an important "antiscreening" (of electron-phonon interaction) effect arising from dynamic screening from the hybrid plasmon-phonon modes. Our calculations show that a significantly higher room-temperature mobility of 300 cm2 V-1 s-1 is possible if high electron densities (>1020 cm-3) with plasmon energies surpassing the highest energy LO mode can be realized. As Ga2O3 and other polar semiconductors play an important role in several device applications, the fundamental understanding of the plasmon-phonon coupling can lead to the enhancement of mobility by harnessing the dynamic screening of the electron-phonon interactions.