Field Dependent Hall Data Research Articles

Double subband occupation of the two-dimensional electron gas in In xAl 1 − xN/AlN/GaN/AlN heterostructures with a low indium content (0.064 ≤ x ≤ 0.140) barrier

We present a carrier transport study on low indium content (0.064 ≤ x ≤ 0.140) In x Al 1 − x N/AlN/GaN/AlN heterostructures. Experimental Hall data were carried out as a function of temperature (33–300 K) and a magnetic field (0–1.4 T). A two-dimensional electron gas (2DEG) with single or double subbands and a two-dimensional hole gas were extracted after implementing quantitative mobility spectrum analysis on the magnetic field dependent Hall data. The mobility of the lowest subband of 2DEG was found to be lower than the mobility of the second subband. This behavior is explained by way of interface related scattering mechanisms, and the results are supported with a one-dimensional self-consistent solution of non-linear Schrödinger–Poisson equations.

Well parameters of two‐dimensional electron gas in Al0.88In0.12N/AlN/GaN/AlN heterostructures grown by MOCVD

AbstractResistivity and Hall effect measurements were carried out as a function of magnetic field (0‐1.5 T) and temperature (30‐300 K) for Al0.88In0.12N/AlN/GaN/AlN heterostructures grown by Metal Organic Chemical Vapor Deposition (MOCVD). Magnetic field dependent Hall data were analyzed by using the quantitative mobility spectrum analysis (QMSA). A two‐dimensional electron gas (2DEG) channel located at the Al0.88In0.12N/GaN interface with an AlN interlayer and a two‐dimensional hole gas (2DHG) channel located at the GaN/AlN interface were determined for Al0.88In0.12N/AlN/GaN/AlN heterostructures. The interface parameters, such as quantum well width, the deformation potential constant and correlation length as well as the dominant scattering mechanisms for the Al0.88In0.12N/GaN interface with an AlN interlayer were determined from scattering analyses based on the exact 2DEG carrier density and mobility obtained with QMSA. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

DX-center energy calculation with quantitative mobility spectrum analysis in n-AlGaAs/GaAs structures with low Al content

Experimental Hall data that were carried out as a function of temperature (60–350 K) and magnetic field (0–1.4 T) were presented for Si-doped low Al content (x=0.14) n–Al x Ga 1− x As/GaAs heterostructures that were grown by molecular beam epitaxy (MBE). A 2-dimensional electron gas (2DEG) conduction channel and a bulk conduction channel were founded after implementing quantitative mobility spectrum analysis (QMSA) on the magnetic field dependent Hall data. An important decrease in 2DEG carrier density was observed with increasing temperature. The relationship between the bulk carriers and 2DEG carriers was investigated with 1D self consistent Schrödinger–Poisson simulations. The decrement in the 2DEG carrier density was related to the DX-center carrier trapping. With the simulation data that are not included in the effects of DX-centers, 17 meV of effective barrier height between AlGaAs/GaAs layers was found for high temperatures (T>300 K). With the QMSA extracted values that are influenced by DX-centers, 166 meV of the DX-center activation energy value were founded at the same temperatures.

Scattering analysis of 2DEG carrier extracted by QMSA in undoped Al0.25Ga0.75N/GaN heterostructures

Hall effect measurements on undoped Al0.25Ga0.75N/GaN heterostructures grown by a metalorganic chemical vapour deposition (MOCVD) technique have been carried out as a function of temperature (20–350 K) and magnetic field (0–1.5 T). Magnetic field dependent Hall data were analysed using the quantitative mobility spectrum analysis (QMSA) technique. The mobility and density within the two-dimensional electron gas (2DEG) at the Al0.25Ga0.75N/GaN interface and within the underlying GaN layer were successfully separated by QMSA. Mobility analysis has been carried out using both the measured Hall data at a single field and the extracted data from QMSA. Analysis of the temperature-dependent mobility of 2DEG extracted from QMSA indicates that the interface roughness and alloy disorder scattering mechanisms are the dominant scattering mechanisms at low temperatures while at high temperatures only polar optical phonon scattering is the dominant mechanism. Al0.25Ga0.75N/GaN interface related parameters such as well width, deformation potential constant and correlation length were also accurately obtained from the fits of the simple analytical expressions of scattering mechanisms to the 2DEG mobility.

Magnetic field dependent Hall data analysis of electron transport in modulation-doped AlGaN/GaN heterostructures

Experimental magnetic field dependent Hall and resistivity data is presented for two modulation-doped AlGaN/GaN heterostructures in the temperature range from 6 to 300 K and for a magnetic field up to 12 T. The mobility and concentration of electrons within the two-dimensional electron gas (2DEG) at the AlGaN/GaN interface and within the underlying GaN layer are readily separated and characterized using quantitative mobility spectrum analysis. The observed transport parameters of the 2DEG are explained using the classical band theory for a degenerate electron gas. Analysis of the temperature dependencies of mobility and electron concentration in the GaN layer and 2DEG indicates that electron transport in the GaN layer is dominated by carriers in the conduction band for the case of low-doping (<1017 cm−3), and by conduction via an impurity band for highly doped material (>1018 cm−3). The simultaneous analysis of the multilayer AlGaN/GaN structure applied in this work renders the results applicable directly to modulation-doped field-effect transistors based on similar structures.

Evaluation of III–V multilayer transport parameters using quantitative mobility spectrum analysis

In this paper we illustrate the power and utility of quantitative mobility spectrum analysis (QMSA) of magnetic field dependent Hall data in order to evaluate the transport parameters of multilayer III–V materials and device structures such as high electron mobility transistors (HEMTs) and heterojunction bipolar transistors (HBTs). As a first example, we present the QMSA of a n +GaAs/GaAs/n +AlGaAs/p +GaAs/n GaAs/n +GaAs HBT structure, in which QMSA resolves two carrier species: holes with mobility of 700 cm 2 V −1 s −1 and density 1.6 × 10 18 cm −3, and electrons with mobility of 1530 cm 2 V −1 s −1 and density 3.0 × 10 18 cm −3. A direct comparison with the results of C-V electrochemical profiling indicates that all n +-type layers (sub-collector, emitter and cap) are characterised by an electron mobility which appears in the mobility spectrum as a single peak with an average density corresponding to the sum of all three n + layers. The peak in the hole spectrum may be clearly identified with the single p-type base layer. The second example is an n −1GaAs/n +AlGaAs/AlGaAs/GaAs HEMT structure in which the 2D electron gas population with a mobility of 7750 cm 2 V −1 s −1 and sheet density of 2.6 × 10 11 cm −2 is readily identified and separated from the mobility spectrum peak corresponding to the two highly-doped n-type capping layers. Due to the similar carrier mobility in both capping layers, their contribution to the spectrum appears as a single electron peak at 1100 cm 2 V −1 s −1 with a density of 2.1 × 10 16 cm −3.

Analysis of magnetic field dependent Hall data in narrow bandgap Hg1−xCdxTe grown by molecular beam epitaxy

The analysis of magnetic field dependent Hall data is presented for three representative Hg1−xCdxTe layers grown by Molecular Beam Epitaxy with x in the range 0.193 to 0.244. These samples exhibit ‘‘anomalous’’ Hall characteristics which are analyzed using a hybrid approach consisting of mobility spectrum (MS) analysis followed by a multi-carrier fitting (MCF) procedure. This hybrid approach is able to readily separate contributions to the total conductivity arising from extrinsic carriers, thermally activated intrinsic electrons, and two-dimensional electron layers. The extracted transport parameters for thermally activated intrinsic electrons are shown to be in excellent agreement with established physical models for narrow bandgap HgCdTe. The two-dimensional electron layers are found to be only weekly temperature dependent with an electron mobility in the range of 2 to 4×104 cm2/V s and a sheet density in the range of 1011 to 1012 cm−2. Of particular interest, is the fact that the ‘‘anomalous’’ Hall characteristics exhibited by all three samples are shown not to be indicative of poor-quality material. This anomalous behavior is found to be due to comparable contributions to the total conductivity from either bulk majority carrier holes and intrinsic minority electrons, or bulk majority carriers and a two-dimensional electron population. The practical aspects of implementing the MS+MCF procedure are discussed, with particular emphasis on the range of magnetic fields required for unambiguous and accurate parameter extraction.

Study of subband electronic structure of Si δ-doped GaAs using magnetotransport measurements in tilted magnetic fields

Si δ-doped GaAs grown by metal organic vapor phase epitaxy (MOVPE) is characterized using magnetotransport measurements in tilted magnetic fields. Angular dependence of the longitudinal magnetoresistance (Rxx) vs the magnetic field (B) traces in tilted magnetic fields is used to examine the existence of a quasi-two-dimensional electron gas. The subband electron densities (ni) are obtained applying fast Fourier transform (FFT) analysis to the Rxx vs B trace and using mobility spectrum (MS) analysis of the magnetic field dependent Hall data. Our results show that (1) the subband electron densities remain roughly constant when the tilted magnetic field with an angle <30° measured from the Si δ-doped plane normal is ramped up to 13 T; (2) FFT analysis of the Rxx vs B trace and MS analysis of the magnetic field dependent Hall data both give the comparable results on subband electron densities of Si δ-doped GaAs with low δ-doping concentration, however, for Si δ-doped GaAs with very high δ-doping concentration, the occupation of the lowest subbands cannot be well resolved in the MS analysis; (3) the highest subband electron mobility reported to date of 45 282 cm2/s V is observed in Si δ-doped GaAs at 77 K in the dark; and (4) the subband electron densities of Si δ-doped GaAs grown by MOVPE at 700 °C are comparable to those grown by MBE at temperatures below 600 °C. A detailed study of magnetotransport properties of Si δ-doped GaAs in the parallel magnetic fields is then carried out to further confirm the subband electronic structures revealed by FFT and MS analysis. Our results are compared to theoretical calculation previously reported in literature. In addition, influence of different cap layer structures on subband electronic structures of Si δ-doped GaAs is observed and also discussed.

Hall effect characterization of LPE HgCdTe P/n heterojunctions

The field and temperature dependence of the Hall coefficient has been used to simultaneously extract information about the p and n layers in very long wave length infrared P/n HgCdTe heterojunctions. The field dependence allows the effects of high mobility electrons to be separated from those of low mobility holes. The higher the magnetic field, the higher the sensitivity to the parameters of the P layer. For a maximum magnetic field of 8000 gauss, the hole sheet concentration must be at least five times the electron sheet concentration to obtain accurate results for the P layer. This criterion is satisfied for typical liquid phase epitaxy (LPE) heterostructures. The analysis determines the hole sheet resistance (concentration times mobility), rather than the hole concentration or mobility separately. Independent knowledge of the P layer thickness and the relationship between hole concentration and resistivity are needed to convert the Hall measurement results to hole concentrations. Analysis of the field-dependent Hall data is complicated by the finding that at least three electrons of different mobilities are needed to fit the field dependence of the Hall coefficient in n-type LPE HgCdTe layers. These results are consistent with previous conclusions that electrons with different mobilities are needed to model bulk n-HgCdTe, and with a range of mobilities in the graded composition interface between the LPE layer and CdTe substrate. Consistent results are obtained for the concentrations and mobilities of the three types of electrons in the n-HgCdTe layer with and without the P layer present. N and P type carrier concentrations are also consistent with dopant concentrations measured by secondary ion mass spectroscopy.

Determination of electrical transport properties using a novel magnetic field-dependent Hall technique

A novel technique is presented for interpreting magnetic field-dependent Hall data at magnetic fields below the range at which Shubnikov–de Haas oscillations occur. The technique generates a ‘‘mobility spectrum’’ in which the maximum carrier density or maximum conductivity is determined as a continuous function of mobility. Examples of the use of the technique with synthetic data as well as data from HgCdTe and GaAs/AlGaAs samples are provided. Other uses of the procedure, including measurement of Fermi surface shapes and direct measurement of the distribution of relaxation times, are discussed.