Quantitative Mobility Spectrum Analysis Research Articles

Al 0.3 Ga 0.7 N/GaN HEMT Yapısı için QMSA Metodu Uygulanması

In this study, Al 0.3 Ga 0.7 N/GaN high electron mobility transistor (HEMT) structure is grown on a sapphire (Al2O3) substrate by using metal-organic vapor phase epitaxy (MOVPE), and its electron transport and magnetic transport properties are investigated. Resistivity is measured in the 20-350 K temperature range. Hall mobility and Hall carrier concentration are measured in the 0-1.5 T magnetic field range and the same temperature range. Magnetic transport properties are analyzed using quantitative mobility spectrum analysis (QMSA). 2DEG and 3DEG transport mechanisms are separated by using QMSA results.

Mixed conductivity analysis of single crystals of α‴-(Cd1−x Znx)3As2 (x = 0.45)

We study the conductivity and magnetoresistance of the α‴ phase solid solution of (Cd1−xZnx)3As2 (x = 0.45). Single crystals of (Cd1−xZnx)3As2 are obtained by the modified Bridgman method. The space group and tetragonal lattice parameters of single crystals are found to be I41/amd and a = b = 8.56(5) Å, c = 24.16(6) Å. The temperature dependence of the conductivity and magnetoresistance is studied in the temperature range of 1.6–320 K and in the presence of a transverse magnetic field from 0 to 10 T. Mixed conductivity is analyzed using Hall resistivity data and standard quantitative mobility spectrum analysis. The concentration and mobility of holes are determined at different temperatures. The presence of two types of holes with different mobilities is demonstrated in the temperature range of 1.6–19 K, while with increasing temperature, just one type of charge carrier is observed in the mobility spectrum.

Locally‐Strain‐Induced Heavy‐Hole‐Band Splitting Observed in Mobility Spectrum of p‐Type InAs Grown on GaAs

High‐quality Be‐doped InAs layer grown by molecular beam epitaxy on GaAs substrate has been examined via magnetotransport measurements and high‐resolution quantitative mobility spectrum analysis (HR‐QMSA) in the range of 5–300 K and up to 15 T magnetic field. The results show four‐channel conductivity and essential splitting of the most populated hole‐like channel below 55 K. It is concluded that origin of such effect results from the locally strain‐induced interlayer, which direct observation is difficult or impossible via alternative techniques. Based on the magnetotransport data analysis, the multilayer model is proposed, which is implemented into nextnano simulation, giving the proof of the argumentation correctness. These results indicate potential usefulness of HR‐QMSA technique even in the degeneration statistic regime.

Temperature dynamics of the electronic structure in dilute Bi-Sn alloys

We study the changes of Bi electronic structure near $T$ and $L$ points of the Brillouin zone caused by doping with Sn (concentrations $\ensuremath{\le}0.08$ at.%). Hall coefficient and magnetoresistance measurements (under magnetic field up to 8 T) enabled calculation of magnetoconductivity tensor components. The usage of quantitative mobility spectrum analysis together with the isotropic approximation for band structure allowed the estimation of Fermi level position at temperatures $10\text{--}300$ K. The results have shown that Sn doping shifts the Fermi level down on the energy scale at the $L$ point (in all temperature range) and at the $T$ point under (primarily at low temperatures), leading to the decrease of band overlap.

Surface conductivity of InAs/GaSb superlattice infrared detectors treated with thiolated self assembled monolayers

The surface conductivity of InAs/GaSb based type II superlattice (T2SL) long wavelength infrared material following the deposition of thiolated self-assembled monolayers (SAMs) of cysteamine, octadecanethiol, dodecanethiol, and hexanethiol are reported. Quantitative mobility spectrum analysis (QMSA) was employed to study the mobility and to isolate and identify surface carriers following SAM treatments on planar samples. QMSA data collected following the deposition of the SAMs on InAs/GaSb material correlates well with dark current measurements, demonstrating the usefulness of QMSA as a tool for evaluating surface conductivity and predicting device performance. All samples displayed a reduction in surface conductivity and dark current density following thiol treatment. Dark current densities were reduced to 1.1 × 10−5, 1.3 × 10−5, 1.6 × 10−5, and 5 × 10−6 A/cm2 for hexanethiol, dodecanethiol, octadecanethiol, and cysteamine, respectively, from 5.7 × 10−4 A cm2 for unpassivated devices.

Characterization and Simulation of Semiconductor Thin Films Using Quantitative Mobility Spectrum Analysis (QMSA)

A quantitative mobility spectrum analysis (QMSA) technique of characterizing mobility and concentration of individual carrier species for modern semiconductor hetero-structures by experimentally generated Hall and resistivity data as a function of magnetic field is presented. QMSA enables the conductivity contribution of bulk majority carriers to be separated from that of carriers present at the surface or at the spacer/barrier layer of GaAs-AlGaAs (2) based HEMTs for characterizing carriers developed in '2' DEG region. Beck and Anderson mobility spectrum analysis (MSA) technique was considered as the first trial function. A variation on the iterative procedure of Dziuba and Gorska is used to obtain the mobility spectrum which shows the quantitatively accurate mobility distribution. QMSA is advantageous because in comparison to its previous counter parts such as MCF, MSA and Dziuba & Gorska; it does not take any prior assumption about the number of electron and hole species as well as their approximate mobilities. A ghost hole along with surface and bulk electron was found in the '2' DEG region developed in HEMTs. In this article, we apply QMSA to both analytical data of Hg1-xCdxTe and real experimental data of AlGaAs obtained from the Hall measurement system. General Terms: QMSA algorithm, Spline Interpolation, Pinning Point, Jacobi's Iteration, Gauss Seidel Iteration Procedure.

Variable-Field Hall Measurement and Transport in LW Single-Layer n-Type MBE Hg1−x Cd x Te

Molecular beam epitaxy n-type long-wavelength infrared (LWIR) Hg1−xCdxTe (MCT) has been investigated using variable-field Hall measurement in the temperature range from 50 K to 293 K. A quantitative mobility spectrum analysis technique has been used to determine the role of multicarrier transport properties with respect to epilayer growth on lattice-matched cadmium zinc telluride, as well as lattice-mismatched silicon (Si) and gallium arsenide (GaAs) buffered substrates. Overall, after postgrowth annealing, all layers were found to possess three distinct electron species, which were postulated to originate from the bulk, transitional (or higher-x-value) regions, and an interfacial/surface layer carrier. Further, the mobility and concentration with respect to temperature were analyzed for all carriers, showing the expected mobility temperature dependence and intrinsic behavior of the bulk electron. Electrons from transitional regions were seen to match expected values based on the carrier concentration of the resolved peak. At high temperature, the lowest-mobility carrier was consistent with the properties of a surface carrier, while below 125 K it was postulated that interfacial-region electrons may influence peak values. After corrections for x-value and doping density at 77 K, bulk electron mobility in excess of 105 cm2 V−1 s−1 was observed in all epilayers, in line with expected values for lightly doped n-type LWIR material. Results indicate that fundamental conduction properties of electrons in MCT layers are unchanged by choice of substrate.

Evaluation of AlGaN/GaN heterostructures properties by QMSA and AFM techniques

Atomic force microscopy and Quantitative Mobility Spectrum Analysis (QMSA) were applied for characterization and evaluation of the quality of AlGaN/GaN heterostructures. The structural uniformity, growth mode and electrical properties of the heterostructures were determined. The obtained results indicated that the time of growth of the low temperature GaN nucleation layer influenced the morphology and electrical properties of the AlGaN/GaN heterostructure.

Electrical transport in InAs/GaSb superlattice: role of surface states and interface roughness

We have modeled electrical properties of InAs/GaSb superlattice (SL) using band structure calculations based on an atomistic empirical pseudopotential method and mobility estimates. The model quantitatively explains the experimental results obtained on a SL sample using the technique of ‘quantitative mobility spectrum analysis (QMSA)’. We show that the factors that influence in-plane electrical transport in this system are different under low- and high-temperature regimes. This difference primarily arises from the location of conducting regions. At lower temperatures the electron density, emanating from the defects in a cap GaSb layer, is essentially confined to a few wells near the surface of the SL. At higher temperatures, conduction is dominated by thermally excited carriers which are more uniformly spread over the entire SL. We identify dominant scattering mechanisms that limit the electron mobility under both regimes and show that interface roughness plays a significant role in the high-temperature regime.

MBE growth and characterization of Mn-doped InN

The majority of InN doping studies have primarily focused on Mg, as it has previously been used to successfully realize p-type GaN. Here, we consider an alternative dopant—Mn—as a possible acceptor candidate in InN. Magnetotransport, x ray photoelectron spectroscopy, and photoluminescence were used to investigate electrical and optical properties of a series of Mn-doped InN thin films grown using molecular beam epitaxy. Evidence of acceptor behavior was observed only for moderate (1017 cm−3) doping levels. At a doping level around 1017 cm−3, light hole features appear in the quantitative mobility spectrum analysis, the surface Fermi level shifts downwards towards the valence band, and low energy features appear in the low temperature photoluminescence spectra.

Band Structure Dependence of Electron Mobility in Modulation-Doped Lattice-Matched InAlAs/InGaAs/InAlAs Heterostructures

Variable-magnetic-field Hall measurements were performed on modulation-doped In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As double heterostructures to investigate the influence of channel layer thickness on the two dimensional electron gas mobility. Quantitative mobility spectrum analysis revealed that the first and second subband mobilities increased with the channel thickness. This enhancement is attributed to the decreased subband effective mass, subband carrier density, and alloy disorder scattering potential.

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.

Bias dependent two-channel conduction in InAlN/AlN/GaN structures

Due to growth temperature differences during deposition of GaN heterostructures utilizing InAlN barriers, an inadvertent parasitic GaN layer can form in the InAlN barrier layer. In structures utilizing AlN spacer layers, this parasitic layer acts as a second conduction channel with a carrier density dependent upon polarization charges and lattice strain as well as the surface potential. The effect of an additional GaN spacer layer in InAlN/AlN/GaN structures is assessed using simulations, electron-microscopy observations, magnetoconductivity measurements with gated Hall bar samples, and with quantitative mobility spectrum analysis. We propose a possible formation mechanism for the parasitic layer, and note that although the additional unintended layer may have beneficial aspects, we discuss a strategy to prevent its occurrence.

Detection of carrier information in heterojunctions of nanocrystalline/crystalline Si

Hall effect measurements on heterojunctions of nanocrystalline Si:H (nc-Si:H) film with crystalline Si wafer fabricated by plasma enhanced chemical vapor deposition technique were made as a function of temperature (20–300 K) and magnetic field (0–15 T). Magnetic field-dependent resistivity and Hall data were interpreted with the quantitative mobility spectrum analysis (QMSA) method, which successfully separated the two-dimensional electron gases (2DEGs) at the nc-Si:H/c-Si interface from 3D carriers appearing in the films and substrates. Mobilities and densities of 2DEGs for the specimens were measured. Detail analyses about influences of interface and epitaxial layer quality including doping, film thickness and mean size of nanocrystals on the mobilities and densities of 2DEGs at interfaces were carried out. The important role of the amorphous buffer layer within the junction was identified. Origin of high mobility observed in the prepared films was revealed. Forward and reverse current mechanisms as well as the dependence of breakdown voltages on temperature in the operated nc-Si:H/c-Si heterostructure were elucidated.

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)

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).

Multicarrier analysis of magnetotransport data at low and high electric fields

AbstractWe present some results on multicarrier analysis of magnetotransport data. Both synthetic as well as data from narrow gap Hg0.8Cd0.2Te samples are used to demonstrate applicability of various algorithms vs. nonlinear least square fitting, Quantitative Mobility Spectrum Analysis (QMSA) and Maximum Entropy Mobility Spectrum Analysis (MEMSA). Comments are made from our experience on these algorithms, and, on the inversion procedure from experimental R/σ‐B to S‐μ specifically with least square fitting as an example. Amongst the conclusions drawn are: (i) Experimentally measured resistivity (Rxx, Rxy) should also be used instead of just the inverted conductivity (σxx, σxy) to fit data to semiclassical expressions for better fits especially at higher B. (ii) High magnetic field is necessary to extract low mobility carrier parameters. (iii) Provided the error in data is not large, better estimates to carrier parameters of remaining carrier species can be obtained at any stage by subtracting highest mobility carrier contribution to σ from the experimental data and fitting with the remaining carriers. (iv)Even in presence of high electric field, an approximate multicarrier expression can be used to guess the carrier mobilities and their variations before solving the full Boltzmann equation. (© 2009 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.

Separation of bulk and surface electron transport in metamorphic InAs layers using quantitative mobility spectrum analysis

Electron transport in low dislocation density, strain-relaxed InAs layers grown on metamorphic InAsyP1−y∕InP substrates by molecular beam epitaxy was characterized using quantitative mobility spectrum analysis (QMSA) of Hall effect measurements. QMSA applied to systematically varied metamorphic InAs samples reveals high bulk electron mobilities of ∼20000cm2∕Vs at 300K at a Si doping concentration of 1×1017cm−3, simultaneously with a separate population of much slower electrons having an average mobility of ∼2400cm2∕Vs due to parallel conduction within the InAs surface electron accumulation layer. Measurements made on higher doped samples reveal only a single electron population participating in transport due to lowered surface band bending that reduces surface accumulation of electrons in conjunction with the high conductivity of the high mobility metamorphic InAs bulk that overwhelms any remaining surface conductivity in the Hall effect measurements.

Growth parameter investigation of Al0.25Ga0.75N/GaN/AlN heterostructures with Hall effect measurements

Hall effect measurements on unintentionally doped Al0.25Ga0.75N/GaN/AlN heterostructures grown by metal organic chemical vapor deposition (MOCVD) were carried out as a function of temperature (20–300 K) and magnetic field (0–1.4 T). Magnetic-field-dependent Hall data are analyzed using the quantitative mobility spectrum analysis (QMSA) technique. The QMSA technique successfully separated electrons in the 2D electron gas (2DEG) at the Al0.25Ga0.75N/GaN interface from other 2D and 3D conduction mechanisms of the samples. 2DEG mobilities, carrier densities and conductivities of the investigated samples are compared at room temperature and low temperature (20 K). For a detailed investigation of the 2DEG-related growth parameters, the scattering analyses of the extracted 2DEG were carried out for all of the samples. Using the results of the scattering analyses, the relation between the growth and scattering parameters was investigated. Increments in the interface roughness (IFR) are reported with the increased GaN buffer growth temperatures. In addition, a linear relation between the deformation potential and interface roughness (IFR) scattering is pointed out for the investigated samples, which may lead to a better understanding of the mechanism of IFR scattering.