Variable Magnetic Field Hall Measurements Research Articles

Separating the Contribution of Mobility among Different Quantum Well Subbands

Variable magnetic field Hall measurements were carried out to investigate carrier transport properties in a modulation-doped In0.53Ga0.47As/In0.52Al0.48As heterostructure over a broad temperature range from 10 to 300 K. Quantitative mobility-spectrum analysis (QMSA) and multicarrier fitting (MCF) analysis were then performed to separately extract information pertaining to the concentration and mobility associated with the first two quantum-well subbands. We thus present an analysis in which the scattering processes are relatively dominated by alloy disorder (optical phonon) for the first (second) subband to best fit the measured roll-over mobility characteristics in the high temperature region (>100 K).

Behavior of rapid thermal annealed ZnO:P films grown by pulsed laser deposition

The transport properties of as-deposited and rapid thermal annealed phosphorus-doped ZnO films grown by pulsed laser deposition are reported. As-grown ZnO:P samples showed n-type characteristics, presumably due to the formation of antisite PZn defects. Rapid thermal annealing yielded a carrier-type conversion from n- to p-type for the ZnO:P films grown at ∼700 °C; samples grown at substantially lower or higher temperatures tended to remain n-type even after the thermal annealing process. The properties and behavior of the n-to-p conversion are most consistent with the formation of PZn-2VZn as the active acceptor state. Variable magnetic field Hall measurements confirmed the p-type behavior. Phosphorus doping concentrations in the range of 0.5−1.0 at. % were considered, with evidence for P segregation in the higher phosphorus concentrations.

Quantitative Mobility Spectrum Analysis of AlGaN/GaN Heterostructures Using Variable-Field Hall Measurements

Carrier transport properties of AlGaN/GaN heterostructures have been analyzed with the quantitative mobility spectrum analysis (QMSA) technique. The nominally-undoped Al0.15Ga0.85N/GaN sample was grown by metal-organic vapor phase epitaxy. Variable-magneticfield Hall measurements were carried out in the temperature range of 4-160 K and magnetic field range of 0-6.6 T. QMSA was applied to the experimental variable-field data to extract the concentrations and mobilities associated with the high-mobility 2DEG and the relatively lowmobility bulk electrons for the temperature range investigated. For temperatures below 100 K the calculated mobility and carrier density values were close to the experimental results. No bulk conduction was observed in this temperature range. At 160 K, QMSA results show that parallel conduction in 3 mm thick GaN layer started to affect the average electron mobility.

Demonstration of nearly non‐degenerate electron conduction in InN grown by molecular beam epitaxy

Electrical characterization of undoped single crystal InN has always exhibited degenerate n-type conductivity. InN layers were grown by molecular beam epitaxy (MBE), and their resistivity and Hall coefficient were measured as a function of magnetic field. The variable magnetic field Hall measurements coupled with multiple-layer modeling allowed the separation of surface, film, and near surface film electrical conduction, and thus was used to remove degenerate conduction associated with surface and interfacial layers. This approach resulted in the measurement of a temperature–dependent mobility and carrier concentration, and constitutes the first detailed measurement of conduction in InN which is only partially degenerate. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Electron localization and resonant tunneling in uniform nanocrystalline silicon quantum dot systems

In this paper, we review our recent investigation of the electronic transport in hydrogenated nanocrystalline silicon thin film grown on crystalline silicon substrate. The variable magnetic-field Hall measurements have been applied to extract the separated carrier information about the nc-Si:H, c-Si and their interface, where the formation of two-dimensional electron gas is clearly observed. With a decrease in the temperature, the nc-Si:H thin film shows a transition from the extended state to the band-tail state, together with a positive magneto-conductivity at extremely low temperatures. These results reveal the good uniformity of the quantum dots in the nc-Si:H thin film and the electron localization. Furthermore, we have successfully observed clear step-like and spike-like structures for the electrons resonant tunneling through the quasi-2D and 0D states in the I– V curves of the nc-Si:H/ c-Si diode under strong electric field at low temperatures.

Investigation of multiple carrier effects in InN epilayers using variable magnetic field Hall measurements

Variable magnetic field Hall effect measurements were performed on InN samples grown by molecular beam epitaxy. Since mixed conduction effects due to both the presence of multiple conducting layers and sample inhomogeneity were present, standard measurements yielded only averaged results. The variable field approach allowed direct measurement of interfacial/surface conduction while also allowing determination of the bulk electrical properties. Analysis always indicated electrons with more than one value of mobility, often with a significant spread in the mobility. This suggests multiple conduction layers in the sample as well as sample inhomogeneity. Variable magnetic field analysis of a 7.5 μm thick InN sample suggests maximum mobilities greater than 4000 cm 2/Vs in “bulk” InN. The quantitative mobility spectrum analysis technique, reported here for the first time on InN, indicated a continuous and significant spread in mobility for the bulk electron, likely with sample thickness.

Laser-beam-induced current mapping of spatial nonuniformities in molecular beam epitaxy As-grown HgCdTe

The formation of dislocations and corresponding built-in electric fields in molecular beam epitaxy (MBE)-grown HgCdTe can have a major impact on the performance and yield of photodetectors fabricated from this material. This paper investigates the presence of such built-in electric fields arising from dislocation segregation in MBE as-grown HgCdTe, and their subsequent removal via a low-temperature Hg-saturated anneal. The electrical properties and surface morphology of an HgCdTe layer grown on a thin CdTe buffer layer are compared with those of an HgCdTe layer grown directly on the CdZnTe substrate. Laser-beam-induced current (LBIC) imaging is a nondestructive technique capable of mapping built-in electric fields present in a semiconductor material, which, in the present case, has been used to reveal dislocation distributions present in as-grown, unintentionally doped, MBE-grown Hg0.71Cd0.29Te. Two-dimensional scanning LBIC measurements at 160 K allow spatial mapping of electric fields across the HgCdTe wafer. Subsequent isothermal annealing of the wafer in an Hg atmosphere has been found to decrease the magnitude of the built-in electric fields to below the LBIC detection limit. However, of particular note, is that before and after annealing, crosshatch patterns can be seen using Nomarski microscopy, with the crosshatching being predominantly in the [01\(\bar 1\)] direction and, to a lesser extent, in the [\(\bar 2\)31] and [\(\bar 2\)13] directions. Defect-decoration etching of the annealed wafer reveals dislocation banding parallel to the [01\(\bar 1\)] direction, which closely resembles the contrast observed in the LBIC image of the wafer before annealing. These Nomarski and LBIC images are compared with those of a second wafer, which incorporates a 40-nm CdTe buffer layer. The second wafer does not show significant Nomarski or LBIC contrast, indicating a flat, electrically uniform as-grown layer. Variable magnetic-field Hall measurements at 77 K and quantitative mobility-spectrum analysis (QMSA) indicate predominately p-type conduction with a doping density of 2×1015 cm−3 in the as-grown layer. After Hg annealing at 240°C, no LBIC signals are observed at 160 K, and Hall measurements at 77 K indicate the presence of two n-type carriers, with a combined doping density of 2×1015 cm−3. Double-crystal x-ray diffraction measurements show no evidence of twinned crystal volumes in the layers before or after annealing, or any change in the full-width at half-maximum (FWHM) (41 arcsec) of the (422) reflection. The similarity between the dislocation density distribution, as revealed by defect decoration, and the LBIC image suggests that Hg out-diffusion during growth is expedited in regions of high dislocation concentration, thus creating a nonuniform Hg vacancy-acceptor concentration. The as-grown acceptor concentration, in turn, modulates the hole concentration, creating p+/p− junctions and built-in electric fields in the material. Low-temperature annealing in a saturated-Hg atmosphere does not remove the crosshatch patterns or dislocation banding, but it fills the Hg vacancies, revealing the uniformly distributed n-type background, thus reducing the magnitude of any built-in electric fields. The LBIC mapping of MBE as-grown HgCdTe samples is, thus, capable of revealing defect distributions that would otherwise require a destructive technique, such as defect-decoration etching, to determine.

Characterization of multiple carriers in GaN using variable magnetic-field hall measurements

Variable magnetic-field Hall-effect measurements were performed on two thick GaN samples grown by hydride vapor-phase epitaxy (HVPE), one freestanding and one attached to the sapphire substrate. Results are compared to those obtained using the more standard, single magnetic-field Hall measurements. In both samples, a second low-mobility electron was indicated that significantly influenced interpretation of single-field Hall measurements, particularly at low temperatures. Extraction of the bulk carrier using fits to the variable-field Hall data allowed a more accurate determination of the temperature dependence of the bulk electrical properties and, hence, basic physical parameters. In addition, the quantitative mobility-spectrum analysis (QMSA) technique, reported here for the first time on GaN, indicated a continuous and significant spread in mobility for the bulk electron, likely with sample thickness. Thus, even the “improved” results, based on modeling the multiple-carrier fitting (MCF) analysis, obtained in this study should be viewed with some suspicion, as they clearly represent an average over an electrically inhomogeneous sample.

Study on the carrier concentration in n-GaAs homojunction multilayer structures by reflection spectroscopy

The temperature-dependent near-band-gap reflection spectroscopy measurements have been used to investigate the carrier information in n-GaAs multilayer structures with different doping concentrations, in addition to the exciton polariton effects in undoped layers. By employing the Fresnel matrix method, we have calculated the experimental reflection spectra and derived the temperature-dependent carrier concentrations of different doping levels. The results are found to coincide with those of variable magnetic field Hall measurements, demonstrating that reflection spectroscopy is another choice to reveal the carrier concentration in multilayer structures with different doping levels.

Evaluation of densities and mobilities for heavy and light holes in p-type Hg1−xCdxTe molecular beam epitaxy films from magnetic-field-dependent Hall data

The densities and mobilities of heavy and light holes have been simultaneously determined at various temperatures (1.2–300 K) in two molecular beam epitaxy-grown p-type Hg1−xCdxTe (x=0.224) samples from variable magnetic-field Hall measurements. The separation of the contribution from the light hole and heavy hole was achieved by a hybrid approach consisting of mobility spectrum analysis followed by a multicarrier fitting procedure. An acceptor energy level at ∼13 meV above the valence band, as well as various mass ratios of light to heavy holes for different temperature were obtained. In addition, the minority carrier (electron) and the surface two-dimensional electron concentrations and mobilities have also been derived as a function of temperature. The explicit experimental values obtained in this work should be useful to physics and modeling of HgCdTe infrared detectors.

HgCdTe extended defects electrical activity characterization by variable magnetic field hall measurements

It has been demonstrated that variable magnetic field Hall measurements for n-Hg 1 − x Cd x Te samples in intrinsic and extrinsic conductivity regions enable the semiquantitative identification and characterization of extended defects of two topological arrangements with either connected or isolated conducting inclusions.

Electrical characterization of very-narrow-gap bulk HgCdTe single crystals by variable magnetic field hall measurements

Variable-magnetic-field Hall measurements (0 to 1.5 T) are performed on very-narrow-gap bulk-grown Hg1−xCdxTe single crystals (0.165 ≤ x ≤ 0.2) at various temperatures (10 to 300K). The electron densities and mobilities are obtained within the one-carrier (electrons) approximation of the reduced-con-ductivity-tensor scheme. The present data together with the selected data set reported by other workers exhibit a pronounced peak when the electron mobility is plotted against the alloy composition x-value which has been predicted to be due to the effective-mass minimum at the bandgap-crossing (Eg ≈ 0). The observed position (x ≈ 0.165), height (≈4 x 102 m2Vs), and width (≈0.01 in x) of the mobility-peak can be explained by a simple simulation involving only ionized-impurity scattering. A lower bound of the effective mass is introduced as a fitting parameter to be consistent with the finiteness of the observed electron mobility and is found to be of the order of 10−4 of the mass of a free electron.