Hall Mobility Measurements Research Articles

SiC-based high electron mobility transistor

This paper describes the fabrication of a SiC-based high electron mobility transistor (HEMT). A single-crystal 3C–SiC layer was grown on a C-face 4H–SiC substrate, and 2D electron gas was induced at the 3C–SiC/4H–SiC heterointerface due to the unique polarization physics. The measured Hall mobility of the 2DEG was 586 cm2/V s at room temperature. Source, gate, and drain electrodes were fabricated on the 3C–SiC surface. The drain current for the fabricated SiC-HEMT was measured to be 47.5 mA/mm, and the transconductance was estimated to be 13.5 mS/mm.

Investigation of the Electronic Properties of Silicon Carbide Films with Varied Si/C Ratios Annealed at Different Temperatures

Hydrogenated amorphous SiC (a-SiC:H) films with various Si/C ratios were prepared using the plasma-enhanced chemical vapor deposition (PECVD) technique. These films were then subjected to thermal annealing at different temperatures to induce crystallization. The electronic properties of the annealed SiC films were investigated through temperature-dependent Hall mobility measurements. It was found that the room-temperature Hall mobilities in the SiC films increased with both the annealing temperature and the Si/C ratio. This increase was attributed to the improved crystallization in the SiC films. Importantly, SiC films with different Si/C ratios annealed at different temperatures exhibited varying temperature dependence behaviors in their Hall mobilities. To understand this behavior, a detailed investigation of the transport processes in SiC films was carried out, with a particular emphasis on the grain boundary scattering mechanisms.

N-type diamond synthesized with tert-butylphosphine for long spin coherence times of perfectly aligned NV centers

The longest spin coherence times for nitrogen-vacancy (NV) centers at room temperature have been achieved in phosphorus-doped n-type diamond. However, difficulty controlling impurity incorporation and the utilization of highly toxic phosphine gas in the chemical vapor deposition (CVD) technique pose problems for the growth of n-type diamond. In the present study, n-type diamond samples were synthesized by CVD using tert-butylphosphine, which is much less toxic than phosphine. The unintentional incorporation of nitrogen was found to be suppressed by incrementally increasing the gas flow rates of H2 and CH4. It was found that the spin coherence time (T2) increased with decreasing the nitrogen concentration, which suggests that the nitrogen concentration limits the length of T2. In the sample with the lowest nitrogen concentration, T2 increased to 1.62 ± 0.10 ms. Optically detected magnetic resonance spectra indicated that all of the measured NV centers were aligned along the [111] direction. Hall measurements confirmed n-type conduction in three measured samples prepared under different growth conditions. The highest measured Hall mobility at room temperature was 422 cm2/(V s). This study provides appropriate CVD conditions for growing phosphorus-doped n-type diamond with perfectly aligned NV centers exhibiting long spin coherence times, which is important for the production of quantum diamond devices.

Boosting the External Quantum Efficiency of AlGaN-Based Metal–Semiconductor–Metal Ultraviolet Photodiodes by Electrode Geometry Variation

Fast aluminum-gallium-nitride–based metal–semiconductor–metal ultraviolet photodiodes were successfully designed, fabricated, and characterized using conventional photolithography techniques. Various electrode geometries were fabricated to investigate the influence of metal contact shapes on the device performance indices with emphasis on the response speed and bias-voltage–independent efficiency. Based on the independently measured Hall mobility and electric field, we evaluated the carrier transit time of the devices as 1.31 ps with bias-voltage–independent external quantum efficiency of 1198% in photoconductive mode at 19.5 V and 70% at 60 V for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula> -doped and intrinsic devices, respectively.

Vacancy-induced enhancement of electron–phonon coupling in cubic silicon carbide and its relationship to the two-temperature model

The electron–phonon coupling factor was calculated for both pristine and vacancy-rich 3C-SiC. Ab initio calculations were performed within the framework of the density functional perturbation theory. Wannier functions were used to interpolate eigenvalues into denser grids through the electron–phonon using Wannier code. The coupling factor was determined through calculations of the electron self-energy, electron–phonon relaxation time, and electronic specific heat. These parameters were extrapolated to high temperatures using a hybrid model which mixes band calculations for electrons below an energy cutoff with the free electron gas model for electrons above the energy cutoff. The electron relaxation times, specific heats, electron drift mobilities, and electron–phonon coupling factors were calculated as a function of electron temperature. Si and C vacancies were found to have a profound effect on electron–phonon coupling for all temperatures, while electronic specific heat capacity was found to be most affected at cryogenic temperatures. The electron drift mobility was calculated at different temperatures using the scattering time. Calculated mobilities were validated with Hall mobility measurements reported in the literature. The importance of structural defects on the electron–phonon coupling is discussed in the context of the two-temperature model, a model that has been widely used to understand aspects of the interaction of solids with pulsed laser irradiation and swift heavy ion irradiation.

Development of Polycrystalline Diamond Compatible with the Latest N-Polar GaN mm-Wave Technology

Integration of diamond on GaN can ease the challenges associated with thermal management of GaN-based power amplifiers which need to base on highly scaled transistors to push toward higher frequencies at high powers for 5G networks. The integration of diamond was achieved by growing polycrystalline (PC) diamond on nitrogen-polar GaN. A standard 5 nm Si3N4 layer which forms the gate dielectric was used as an interlayer between diamond and the GaN channel for etching protection. Since diamond growth conditions involve high temperature and H2 plasma, it can easily decompose the underlying dielectric as well as the GaN channel and degrade the channel conductivity and hence the device performance. Due to the incompatibility of conventional growth recipes with thin dielectrics (<5 nm), a novel two-stage-three-step growth recipe was designed for PC diamond integration on top of nitrogen-polar GaN high-electron-mobility transistors in a H2/CH4-plasma environment. Using only H2 and CH4 in the chamber guarantees a higher-phase-purity diamond than chambers with added argon or nitrogen for lower substrate etching. This recipe maintains the performance of the two-dimensional-electron gas and provides a less columnar diamond structure with a larger grain size. Our observations were supported by scanning transmission electron microscopy and Hall mobility measurements using the van der Pauw technique before and after diamond growth. A mobility of ∼1250 cm2/V s, a sheet carrier concentration of ∼1.30 × 1013 cm–2, and a sheet resistivity of ∼380 Ω/□ were maintained after the growth of diamond. The anisotropy ratio has been decreased from 3.75 to 1.12 with this growth recipe. Using long channel devices, we measured the difference in the channel temperature, which decreased by more than 100 °C in the range of 10–24 W/mm power after the integration of the diamond on top of the device.

Mobility of near surface MOVPE grown InGaAs/InP quantum wells

In this work, we study the electron mobility of near surface metal organic vapor phase epitaxy-grown InGaAs quantum wells. We utilize Hall mobility measurements in conjunction with simulations to quantify the surface charge defect density. Buried quantum wells are limited by polar optical phonon scattering at room temperature. In contrast, the quantum wells directly at the surface are limited by remote charge impurity scattering from defects situated at the III–V/oxide interface or inside the oxide, showing a mobility of 1500 cm2/V s. Passivating the InGaAs surface by depositing an oxide reduces the amount of defects at the interface, increasing the mobility to 2600 cm2/V s.

Gated Hall and field-effect transport characterization of e-mode ZnO TFTs

Two methods of measuring the electronic transport properties of a material are transistor DC-voltage and the Hall effect. Hall mobility measurements of normally off semiconductors can be done by electrostatic doping to lower resistance in the channel. We show that by measuring both, we can compare any value (raw measured as well as calculated data) directly to any other value along an index of FET gate and drain voltage across the entire safe operating area of the device. Our gated Hall technique intrinsic calculations of Hall mobility, typically possible only for bulk or doped materials, for thin-film transistor materials stack up with thickness scaled to practical values.

Inkjet-printed graphene Hall mobility measurements and low-frequency noise characterization

We report room temperature Hall mobility measurements, low temperature magnetoresistance analysis and low-frequency noise characterization of inkjet-printed graphene films on fused quartz and SiO2/Si substrates. We found that thermal annealing in vacuum at 450 °C is a necessary step in order to stabilize the Hall voltage across the devices, allowing their electrical characterization. The printed films present a minimum sheet resistance of 23.3 Ω sq-1 after annealing, and are n-type doped, with carrier concentrations in the low 1020 cm-3 range. The charge carrier mobility is found to increase with increasing film thickness, reaching a maximum value of 33 cm2 V-1 s-1 for a 480 nm-thick film printed on SiO2/Si. Low-frequency noise characterization shows a 1/f noise behavior and a Hooge parameter in the range of 0.1-1. These results represent the first in-depth electrical and noise characterization of transport in inkjet-printed graphene films, able to provide physical insights on the mechanisms at play.

Ballistic InSb Nanowires and Networks via Metal-Sown Selective Area Growth.

Selective area growth is a promising technique to realize semiconductor-superconductor hybrid nanowire networks, potentially hosting topologically protected Majorana-based qubits. In some cases, however, such as the molecular beam epitaxy of InSb on InP or GaAs substrates, nucleation and selective growth conditions do not necessarily overlap. To overcome this challenge, we propose a metal-sown selective area growth (MS SAG) technique, which allows decoupling selective deposition and nucleation growth conditions by temporarily isolating these stages. It consists of three steps: (i) selective deposition of In droplets only inside the mask openings at relatively high temperatures favoring selectivity, (ii) nucleation of InSb under Sb flux from In droplets, which act as a reservoir of group III adatoms, done at relatively low temperatures, favoring nucleation of InSb, and (iii) homoepitaxy of InSb on top of the formed nucleation layer under a simultaneous supply of In and Sb fluxes at conditions favoring selectivity and high crystal quality. We demonstrate that complex InSb nanowire networks of high crystal and electrical quality can be achieved this way. We extract mobility values of 10 000-25 000 cm2 V-1 s-1 consistently from field-effect and Hall mobility measurements across single nanowire segments as well as wires with junctions. Moreover, we demonstrate ballistic transport in a 440 nm long channel in a single nanowire under a magnetic field below 1 T. We also extract a phase-coherent length of ∼8 μm at 50 mK in mesoscopic rings.

Improvement of Low‐Temperature zT in a Mg3Sb2–Mg3Bi2 Solid Solution via Mg‐Vapor Annealing

Materials with high zT over a wide temperature range are essential for thermoelectric applications. n-Type Mg3 Sb2 -based compounds have been shown to achieve high zT at 700 K, but their performance at low temperatures (<500 K) is compromised due to their highly resistive grain boundaries. Syntheses and optimization processes to mitigate this grain-boundary effect has been limited due to loss of Mg, which hinders a sample's n-type dopability. A Mg-vapor anneal processing step that grows a sample's grain size and preserves its n-type carrier concentration during annealing is demonstrated. The electrical conductivity and mobility of the samples with large grain size follows a phonon-scattering-dominated T-3/2 trend over a large temperature range, further supporting the conclusion that the temperature-activated mobility in Mg3 Sb2 -based materials is caused by resistive grain boundaries. The measured Hall mobility of electrons reaches 170 cm2 V-1 s-1 in annealed 800 °C sintered Mg3 + δ Sb1.49 Bi0.5 Te0.01 , the highest ever reported for Mg3 Sb2 -based thermoelectric materials. In particular, a sample with grain size >30 mm has a zT 0.8 at 300 K, which is comparable to commercial thermoelectric materials used at room temperature (n-type Bi2 Te3 ) while reaching zT 1.4 at 700 K, allowing applications over a wider temperature scale.

Investigation of DC and RF Performance of Novel MOSHEMT on Silicon Substrate for Future Submillimetre Wave Applications

In this work, the DC and RF performance of a 20 nm gate length novel metal oxide semiconductor high electron mobility transistor (MOSHEMT) on Silicon substrate is studied using Sentaurus TCAD tool. The proposed MOSHEMT device features a novel T-gate structure, heavily doped In0.52Ga0.48As source/drain regions, delta doped planes on both sides of the In0.75Ga0.25As/InAs/In0.75Ga0.25As composite channel, a multi layer cap and a very thin layer of HfO2 as gate dielectric. The TCAD simulation results obtained at room temperature using hydrodynamic carrier transport model indicates that the 20 nm gate length proposed MOSHEMT device is capable of providing a peak drain current of 2450 mA/mm at VDS = 0.6 V and the peak transconductance obtained for the proposed device is 2900 mS/mm. The fT and fmax obtained for the Lg = 20 nm proposed MOSHEMT on Silicon substrate are 372 and 480 GHz respectively. At 300 K, the measured Hall mobility of the electrons in the quantum well channel is 9600 cm2/(V s). The on state resistance (RON) obtained for the Lg = 20 nm proposed device is 116 Ohm μm. These devices are undoubtedly, the most suitable candidates for future sub millimetre wave applications.

Temperature Dependent Electrical Transport Properties of High Carrier Mobility Reduced Graphene Oxide Thin Film Devices

We report temperature dependent electrical transport properties of high mobility reduced graphene oxide (RGO) thin films fabricated by pulse laser deposition. The temperature dependent (5K–350K) four terminal electrical transport property measurements confirm variable range hopping and thermally activated transport mechanism of the charge carriers at low (5K–210K) and high temperature (210K–350K) regions, respectively. The calculated localization length, the density of states near the Fermi level ( $E_{F}$ ), hopping energy, and Arrhenius energy gap provide useful information to explain the excellent electrical properties of the RGO films. Hall mobility measurement confirms ${p}$ -type characteristics of the thin films. The charge carrier Hall mobility can be engineered by tuning the growth parameters, and the measured maximum mobility was 1596 cm2v−1s−1. The optimization of the improved electrical property is well supported by structural properties such as the defect density, average size of sp2 clusters and degree of reduction, which were investigated by Raman spectroscopy and X-ray diffraction analysis.

Electron mobility in β-Ga2O3: an ensemble Monte Carlo study

Numerical simulations are performed to evaluate electron mobility in β-Ga2O3. Following scattering mechanisms were found to be important: acoustic deformation potential, ionized impurity, and polar optical phonons. In β-Ga2O3, a large primitive unit cell (containing ten atoms) leads to multiple phonon modes, which complicate the mobility calculation. Here, by restructuring an in-house ensemble Monte Carlo simulator, we were able to include and examine the effects of all relevant longitudinal optical phonon modes. For low electrical fields at 300 K, we report an electron mobility of 110 cm2/V s. Also, in the range of 150‒500 K, our simulation results match very well with the reported Hall mobility measurement data.

Boosting Ge-Epi P-Well Mobility & Crystal Quality with Si or Sn Implantation and Melt Annealing

We investigated the effects of Sn, Si and C7 implantation into both P-well and N-well doped regions of Ge-epi on Si wafers after RTA and laser annealing, on crystal quality using XRD analysis and mobility using ALPro profiler of Active Layer Parametrics , which provides mobility and carrier concentration profiles at sub-nm resolution. SIMS analysis was also used for chemical depth analysis. XRD analysis shows improved Ge-epi crystallinity after >1.5J/cm2 laser melt annealing (liquid phase epitaxial regrowth). Since µ=1/ρqN where µ=mobility (cm2/volt-sec), ρ=resistivity (ohm-cm), q=charge of an electron and N=dopant concentration (cm3), if we assume qN=K a constant for these low dopant well regions then we can estimate change in mobility based on change in P-well or N-well resistance then compare to mobility measured by ALPro profiler. For the P-well cases doped with B=5keV at 1E13/cm2 dose for a retrograde P-well ~1E18/cm3 the Ge-epi Rs decreased to 1,600Ω/□ compared to Si at 3,400Ω/□ suggesting a hole mobility increase of 2.1x from 150cm2/V-s to 315cm2/V-s based on literature with actual measured Hall mobility of 465.2cm2/V-s, an increase of 3.1x. The 1.8J/cm2 laser melt anneal boosted P-well Hall mobility by 22% to 567cm2/V-s to a depth of 80nm and adding Sn implant improved mobility 91% to 889cm2/V-s and at a depth beyond 80nm mobility increases to 3,000cm2/V-sec. Si implant improved mobility by 43% to 667cm2/V-s to a depth of >100nm. For the N-well cases doped with P=40keV at 1E13/cm2 dose for a retrograde N-well ~1E18/cm3 the Ge-epi Rs increased to 2,000Ω/□ compared to Si at 1,600Ω/□ suggesting an electron mobility decrease of 0.8x to 216cm2/V-s rather than the expected increase of 3.3x from 270cm2/V-s for Si to 900cm2/V-s for Ge reported in the literature and expected N-well Rs of 485Ω/□. The actual Ge-epi N-well Hall mobility measured was 449cm2/V-s so only a 1.7x increase and nearly identical to the P-well mobility of 465cm2/V-s but the mobility drops off beyond a depth of 40nm. The 1.8J/cm2 laser melt anneal reduces N-well mobility to 191cm2/V-s but is uniform to a depth of 70nm. Adding Si implant had a slight decrease in mobility to 183cm2/V-s while Sn implant increases mobility to 280cm2/V-s uniformly to a depth >100nm. C7 (cluster-C) implant reduced N-well surface mobility to 50.3cm2/V-s to a depth of 30nm but then mobility increases 10x up to ~500cm2/V-s to a depth of 80nm and then drops to ~100cm2/V-s in the non-carbon N-well region as revealed by C-SIMS analysis to a depth of 110nm, therefore measuring mobility versus depth can be very critical in engineering surface and bulk mobility improvements based on chemical compositional changes in the Ge-epilayer. B-SIMS analysis shows retrograde P-well profile with 2E18/cm3 Rp at 50nm and Xj at 150nm also the Ge/Si epilayer interface. The laser melt flattens the B P-well profile to ~1E18/cm3 with a B pile-up at ~2E18/cm3 at the Ge/Si interface. C-SIMS analysis revealed only slight to no C diffusion even in the liquid Ge-melt phase while we observe 2-5% Si intermixing in the Ge-melt but no B nor P diffusion when C was present. Additional results for RTA anneals will be presented.

Boosting Ge-Epi P-Well Mobility & Crystal Quality with Si or Sn Implantation and Melt Annealing

We investigated the effects of Si, Sn and cluster-C implantation into both P-well and N-well doped regions of Ge-epi on Si wafers after laser annealing. XRD analysis shows improved Ge-epi crystallinity after >1.5J/cm2 laser melt annealing (liquid phase epitaxial regrowth) compared to sub-melt annealing (solid phase epitaxial regrowth). For the P-well case the Ge-epi Rs decreased to 1,600Ω/□ compared to Si at 3,400Ω/□ suggesting a hole mobility increase of 2.1x from 150cm2/V-s to 315cm2/V-s but actual measured Hall mobility was 650cm2/V-s to a depth of 60nm, an increase of 4.3x. The 1.8J/cm2 laser melt anneal with Si implant improved mobility uniformly to 700cm2/V-s to a depth of 100nm while Sn implant improved mobility to 900cm2/V-s from the Ge-epi surface to a depth of 70nm then increases to 3000cm2/V-s at a depth of 100nm. Measuring mobility depth profiles can be very critical in engineering surface and bulk mobility improvements which can be determined by chemical compositional changes in the Ge-epilayer especially for C where no liquid phase diffusion or movement could be detected.

Simultaneous Enhancement of Electrical Conductivity and Seebeck Coefficient of [6,6]-Phenyl-C71 Butyric Acid Methyl Ester (PC70BM) by Adding Co-Solvents

Chemical modification by co-solvents added to [6,6]-Phenyl-C71 butyric acid methyl ester, commonly known as an n-type semiconducting fullerene derivative PC70BM, is reported to change the electrical and thermoelectric properties of this system. Power factor of the casted PC70BM samples achieves values higher than that determined for a variety of organic compounds, including conducting polymers, such as PEDOT:PSS in the pristine form. After chemical functionalization by different solvents, namely N,N-Dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-Methyl-2-pyrrolidone (NMP), acetonitrile (AC), and 1,2-Dichloroethane (DCE), the four-probe in-plane electrical conductivity and Seebeck coefficient measurements indicate a simultaneous increase of the electrical conductivity and the Seebeck coefficient. The observed effect is more pronounced for solvents with a high boiling point, such as N,N-Dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and N-Methyl-2-pyrrolidone (NMP), than in acetonitrile (AC) and 1,2-Dichloroethane (DCE). We identified the origin of these changes using Hall mobility measurements, which demonstrate enhancement of the PC70BM charge carrier mobility upon addition of the corresponding solvents due to the improved packaging of the fullerene compound and chemical interaction with entrapped solvent molecules within the layers.

Chemical and semiconducting properties of NO2-activated H-terminated diamond

The H-terminated surface of diamond when activated with NO2 produces a surface conduction layer that has been used to make field effect transistors (FETs). Previous reports have suggested that during NO2 exposure (NO2-activation), NO2− forms on the diamond surface and generates positive carriers (holes) in the diamond, making the diamond surface conductive. We report here on X-ray-photoelectron-spectroscopy (XPS) surface characterization of single crystal diamonds and on infrared absorption of diamond powder. After activation, XPS showed the presence of N atoms on the diamond surface, but infrared absorption found no evidence of NO2−, but instead NO3− is present on the diamond surface.Two wet chemistry techniques determined the concentration of NO3− per milligram of diamond powder. With the powder's surface area measured by the BET technique, the surface NO3− concentration was measured to be between 6.2 × 1013 and 8.2 × 1013 cm−2. This is in the same range as the carrier densities, 3 × 1013 to 9 × 1013 cm−2, determined by Hall mobility and surface conductivity measurements of single crystal diamonds. Using similar techniques, the concentration of NO2− was determined to be <1012 cm−2.Both the surface conductance and the surface H atoms are stable in dry nitrogen, with or without NO2-activation, but the surface conductance, the concentrations of H atoms both with and without activation and NO3− decrease when exposed to laboratory air over a period of hours to days. Infrared absorption measurements showed the reduction of surface NO3− and H atoms during laboratory air exposure, but gave no indication of what reactions are responsible for their loss in laboratory air.

Low temperature sputter-deposited ZnO films with enhanced Hall mobility using excimer laser post-processing

We report the low temperature (T < 70 °C) fabrication of ZnO thin films (~140 nm) with Hall mobility of up to 17.3 cm2 V−1 s−1 making them suitable for thin film transistor (TFT) applications. The films were deposited by rf magnetron sputtering at T < 70 °C and subsequently laser processed in ambient temperature in order to modify the Hall mobility and carrier concentration. Medium-to-low energy laser radiation densities and a high number of pulses were used to avoid damaging the films. Laser annealing of the films after aging in the lab under 25%–35% relative humidity and at an average illuminance of 120 lux resulted in an overall higher mobility and relatively low carrier concentration in comparison to the non-aged films that were laser processed immediately after deposition. A maximum overall measured Hall mobility of 17.3 cm2 V−1 s−1 at a carrier density of 2.3 × 1018 cm−3 was measured from a 1 GΩ as deposited and aged film after the laser treatment. We suggest that the aging of non-processed films reduces structural defects mainly at grain boundaries by air species chemisorption, with concomitant increase in thermal conductivity so that laser processing can have an enhancing effect. Such a processing combination can act synergistically and produce suitable active layers for TFT applications with low temperature processing requirements.

Growth, structural, and electrical properties of germanium-on-silicon heterostructure by molecular beam epitaxy

The growth, morphological, and electrical properties of thin-film Ge grown by molecular beam epitaxy on Si using a two-step growth process were investigated. High-resolution x-ray diffraction analysis demonstrated ∼0.10% tensile-strained Ge epilayer, owing to the thermal expansion coefficient mismatch between Ge and Si, and negligible epilayer lattice tilt. Micro-Raman spectroscopic analysis corroborated the strain-state of the Ge thin-film. Cross-sectional transmission electron microscopy revealed the formation of 90 ° Lomer dislocation network at Ge/Si heterointerface, suggesting the rapid and complete relaxation of Ge epilayer during growth. Atomic force micrographs exhibited smooth surface morphology with surface roughness &amp;lt; 2 nm. Temperature dependent Hall mobility measurements and the modelling thereof indicated that ionized impurity scattering limited carrier mobility in Ge layer. Capacitance- and conductance-voltage measurements were performed to determine the effect of epilayer dislocation density on interfacial defect states (Dit) and their energy distribution. Finally, extracted Dit values were benchmarked against published Dit data for Ge MOS devices, as a function of threading dislocation density within the Ge layer. The results obtained were comparable with Ge MOS devices integrated on Si via alternative buffer schemes. This comprehensive study of directly-grown epitaxial Ge-on-Si provides a pathway for the development of Ge-based electronic devices on Si.