Electron Mobility In GaAs Research Articles

Subnanosecond switching of GaAs diode due to impact ionization in collapsing bipolar Gunn domains

Subnanosecond switching of GaAs diode due to impact ionization in collapsing bipolar Gunn domains

Investigating the effects of impurity on electron mobility in quasi-one-dimensional wires

In this research, the electron mobility in GaAs quasi-one-dimensional wires with the presence of ionized impurity at zero temperatures was investigated and the results were compared with the mobility of a two-dimensional electron gas system. GaAs is a non-magnetic semiconductor with a direct band gap. Here for the calculations, the Boltzmann transport equation is used in the relaxation time approximation, taking into account the ionized impurity potential. Focusing on ionized Coulomb scattering and the short-range disorder is our goal. Electron mobility was investigated based on related parameters (Fermi energy and width of nanowires), and its diagram was drawn. In the end, the results of this research were compared with electron mobility in completely two-dimensional electronic systems. As expected, the numerical results showed that the electron mobility in extensive wires converges to the electron gas mobility of a fully two-dimensional plane.

A quantitative analysis of electronic transport in n- and p-type modulation-doped GaAsBi/AlGaAs quantum well structures

Electronic transport properties of as-grown and thermally annealed n- and p-type modulation-doped GaAsBi/AlGaAs quantum well (QW) structures were investigated. Hall mobility of as-grown, n- and p-type modulation doped QW structures are found from raw experimental data as ∼1414 and 95 cm2 Vs−1 at room temperature. A comparison between reported two-dimensional (2D) electron density determined from the analyses of Shubnikov de Haas oscillations and the 2D Hall electron density indicates a presence of parallel conduction in barrier layer (AlGaAs) and QW layer (GaAsBi) in n-type samples, therefore a parallel channel conduction theory is used to separate the electron mobility in the QW and the barrier layers in n-type modulation doped GaAsBi/AlGaAs QW structure. The extracted electron mobility of the as-grown n-type GaAsBi/AlGaAs QW sample is determined as ∼5975 cm2 Vs−1 at 4.2 K, which is closer to the electron mobility in GaAs. It is found that thermal annealing at lower temperature than growth temperature increases electron mobility of 2D electron gas, while annealing at higher temperature than growth temperature decreases electron mobility. The temperature dependence of the extracted electron mobility using parallel conduction approximation is analytically calculated by considering possible scattering mechanisms. Analysis of temperature-dependent electron mobility shows that the dominant scattering mechanisms are interface roughness (IFR), acoustic, and alloy-potential scatterings at low and intermediate temperature range, and IFR and optical phonon scattering at the high-temperature range in n-type modulation doped GaAsBi/AlGaAs QW structures.

Ab initio electron-two-phonon scattering in GaAs from next-to-leading order perturbation theory

Electron-phonon (e–ph) interactions are usually treated in the lowest order of perturbation theory. Here we derive next-to-leading order e–ph interactions, and compute from first principles the associated electron-two-phonon (2ph) scattering rates. The derivations involve Matsubara sums of two-loop Feynman diagrams, and the numerical calculations are challenging as they involve Brillouin zone integrals over two crystal momenta and depend critically on the intermediate state lifetimes. Using Monte Carlo integration together with a self-consistent update of the intermediate state lifetimes, we compute and converge the 2ph scattering rates, and analyze their energy and temperature dependence. We apply our method to GaAs, a weakly polar semiconductor with dominant optical-mode long-range e–ph interactions. We find that the 2ph scattering rates are as large as nearly half the value of the one-phonon rates, and that including the 2ph processes is necessary to accurately predict the electron mobility in GaAs from first principles.

(Invited) Toward High Frequency and High Power Flexible Electronics

Radio frequency (RF) devices have been widely used for commercial wireless communication and military electronics. With the rapid development of wireless communication and radar technology, RF transistors for higher frequency and higher power applications are in demand. Meanwhile, the emerging market of wearable devices and internet of things (IoT) require electronic systems including RF parts to be in flexible or bendable form. Conventional semiconductors for flexible electronics like oxide semiconductors, and amorphous/poly Si and organic semiconductors cannot meet the requirement of wireless communication at the GHz range due to their low electron mobility (0.1 ~ 10 m2/V∙s). To fabricate high frequency flexible transistors, single crystal semiconductor nanomembranes have attracted great attention due to their high electron mobility (>100 m2/V∙s). Our group has reported GHz thin film Si MOSFET with an fT of 1.9 GHz and a maximum oscillation frequency (fmax ) of 3.1 GHz by transferring Si nanomembrane from a silicon-on-insulator wafer to a flexible plastic substrate. To further improve the performance of flexible RF Si MOSFETs, different device structures have been investigated. A strained Si nanomembrane channel has been demonstrated to enhance electron mobility. Flexible Si MOSFET with strained channel has shown an fT of 5.1 GHz and fmax of 15.1 GHz. Gate trench Si MOSFETs using nanoimprint technology has been successfully fabricated. By reducing the gate trench to 100 nm, the transistor shows an fT of 5 GHz and fmax of 38 GHz. Besides Si, we have also fabricated GaAs-based thin film heterojunction bipolar transistors (HBTs) for flexible RF electronics due to the high electron mobility of GaAs. We have successfully demonstrated thin film GaAs HBTs on biodegradable cellulose nanofibril (CNF) substrates by the transfer printing technique. HBTs on CNF substrate show an fT of 37.5 GHz and fmax of 6.9 GHz, facilitating use in GHz range applications. The reported flexible RF transistors based on Si and GaAs thin film have shown the capability of working at the GHz range. However, due to a small bandgap and low breakdown field, they are not suitable for high power applications at high frequency. GaN has been rapidly developed for high-frequency and high-power applications due to its large bandgap, high breakdown field, high electron mobility, and high electron saturation velocity of two dimensional electron gas (2DEG). Several flexible AlGaN/GaN HEMTs have been fabricated by the transfer printing AlGaN/GaN thin film to flexible substrate. Our group have reported flexible RF AlGaN/GaN HEMT on PET substrate with an fT of 60 GHz and fmax of 115 GHz. A layer of 3.5 µm intrinsic single crystalline GaN thin film was used as the heat spreading layer for the HEMT due to large thermal conductivity of single crystalline GaN. The HEMT can successfully work under 0.5 W, which indicates the potential use of AlGaN/GaN HEMTs in high-frequency and high-power flexible electronics. We further combined flexible RF AlGaN/GaN HEMTs with environmental friendly green flexible substrates to fabricate flexible green RF electronics for high-power applications. We successfully fabricated a 500 µm × 500 µm AlGaN/GaN HEMT on biodegradable CNF substrate using the transfer printing technique. The HEMT can achieve an fT and fmax of 40 GHz and 79 GHz, respectively, and work under 0.3 W on CNF substrate. To further exploit the application of flexible green RF AlGaN/GaN HEMTs, we fabricated a flexible RF power amplifier based on the HEMT. The RF power amplifier was fabricated by combining the flexible HEMT and impedance matching network consisting of a spiral inductor and metal-insulator-metal (MIM) capacitor on a temporary Si substrate with a PMMA sacrificial layer. After dissolving the PMMA sacrificial layer, the entire RF power amplifier (~10 µm thick) was transfer printed on a CNF substrate. The RF power amplifier on CNF substrate shows a small signal gain of ~6 dB from 5 GHz to 6 GHz. The RF power performance measurement shows it can deliver an RF power of ~10 mW with peak power added efficiency (PAE) of 4% at 5.5 GHz. The recent progress of flexible RF AlGaN/GaN HEMTs and RF power amplifiers will significantly advance the development of flexible electronics for high-frequency and high-power applications.

Femtosecond-timescale buildup of electron mobility in GaAs observed via ultrabroadband transient terahertz spectroscopy

The buildup of photoconductivity in an archetypal polar semiconductor GaAs was monitored on the timescale of carrier-carrier and carrier-lattice correlations, with sub-50 fs temporal resolution provided by ultra-broadband transient terahertz spectroscopy. Two relevant timescales are identified: the transition in photoconductivity from a regime of extremely weak screening to a screened Drude plasma was observed on the ∼280 fs timescale, followed by the gradual increase and saturation of electron mobility on a timescale of ∼160 fs. The Drude photoconductivity picture following carrier photoinjection was found to stabilize only on the timescale corresponding to several lattice and plasma oscillations.

(Invited) Monolithic Integration of n-In0.53Ga0.47As and p-Ge FinFETs on Si

With continuous increase in transistor count and clock frequency, the power density of current Si integrated circuits has reached a level that calls for a revolutionary change in transistor technology. High hole mobility Ge and high electron mobility InGaAs have been considered to be the most promising channel materials for p-channel and n-channel MOSFETs, respectively. Selective-area growth (SAG) on nano-trenches has been quite popular in integrating III-V materials with Si substrates. Since there exists a high lattice mismatch between III-V materials and Si, obtaining defect-free epilayer is still a great challenge. In this work, we demonstrate selective area growth of InGaAs on Ge trenches aiming at integrating n-channel InGaAs FinFETs and p-channel Ge FinFETs side by side on a Si substrate for CMOS applications. The Ge templates, which were grown on Si by chemical vapor deposition, were prepared by etching through an oxide mask using a dilute H2O2 solution to create Ge linear trench structures with embedded {111} facets at the bottom of the trenches for facilitating the regrowth of III-V materials. The III-V materials were selectively grown on the patterned Ge templates by metal-organic vapor phase epitaxy. An InGaP buffer layer, which has a wide bandgap and is beneficial for electrical isolation between the channel and substrate, was grown onto the Ge trenches. Undoped InGaAs was grown on InGaP as the n-channel material. High resolution transmission microscopy investigations show that very few dislocations are present near the Ge/InGaP interface in the trenches. It is found that In content of InGaP increases from 50 % to about 70 % with growth as evidenced by energy-dispersive x-ray spectroscopy (EDX). Interestingly, composition grading is also observed on the subsequently grown InGaAs. It begins from an In0.21Ga0.79As layer, which has good lattice match to the In0.7Ga0.3P layer beneath, then changes to the nominal In0.71Ga0.29As layer near the top of the fin. The strain in InGaAs is partially released through the generation of dislocations near the InGaAs/InGaP interface, leading to a nearly defect-free region at the top of the fin. A growth mechanism is proposed to account for the correlation between strain accommodation, composition grading, and defects generation.

Ge technology beyond Si CMOS

To save energy, low voltage operation is the most important criterion for CMOS ICs. To reach this goal, high mobility new channel materials are required for CMOS ICs at ≤ 14 nm technology nodes. The high electron mobility InGaAs nMOSFET and high hole mobility Ge pMOSFET were proposed for CMOS at 0.5 V operation, since the poor hole mobility of InGaAs makes it unsuitable for all InGaAs CMOS. However, the epitaxial InGaAs nMOSFET on Si faces fundamental material challenges with large defects and high leakage current. Although dislocation-defects-free Ge-on-Insulator (GeOI), ultra-thin-body (UTB) InGaAs IIIV-on-Insulator (IIIVOI), and selective GeOI on Si were pioneered by us, it is still difficult to reach InGaAs-nMOS/Ge-pMOS CMOS targeting to ≤ 14 nm CMOS. In contrast, Ge is the ideal candidate for all Ge CMOS logic due to both higher electron and hole mobility than Si. Significantly higher (2.6X) hole mobility of GeOI pMOSFET than universal SiO2/Si value was reached at a medium 0.5 MV/cm effective electric field (Eejf) and 1.4 nm equivalent-oxide-thickness (EOT). Nevertheless, the Ge nMOSFET suffers from large EOT and fast mobility degradation with increasing Eeff, due to the surface Fermi-level pinning to valance band, poor high-κ/Ge interface and low dopant activation. Using novel laser annealing and proper gate stack, small EOT of 0.95 nm, small sub-threshold swing of 106 mV/dec, and 40% better high-field mobility than universal SiO2/Si data were achieved in Ge nMOSFET. Such all-Ge CMOS has irreplaceable merits of much simpler process, lower cost, and potentially higher yield than the InGaAs-nMOS/Ge-pMOS CMOS platform.

Growth and properties of the dilute bismide semiconductor GaAs<SUB align=right>1−xBi<SUB align=right>x a complementary alloy to the dilute nitrides

In this review we describe the growth and properties of the dilute bismide semiconductor alloy GaAs1−xBix and show how its properties are in certain respects complementary to the dilute nitride alloy, GaNyAs1−y. Like the dilute nitrides the dilute bismides show a giant band gap bowing effect in which a small concentration of the alloying element has a disproportionate effect on the band gap, however in the case of the bismide the band gap reduction is associated with an increase in the energy of the valence band maximum (VBM) rather than a reduction in the energy of the conduction band minimum (CBM). Under standard GaAs growth conditions Bi acts as a surfactant with associated improvements in surface quality. In order to incorporate Bi, growth temperatures below 400°C are used with As2/Ga flux ratios close to unity. The electron mobility of GaAs is only weakly affected by Bi alloying, in contrast to the dilute nitrides where the electron mobility decreases rapidly with N alloying. Bi alloying also produces a giant bowing effect in the spin orbit splitting in the valence band. Strong room temperature photoluminescence is observed. Prospects for future device applications of this new compound semiconductor alloy are discussed.

Total Dielectric Function Approachto the Electron Boltzmann Equation for Scatteringfrom a Two‐Dimensional Coupled Mode System

The nonequilibrium total dielectric function lends itself to a simple and general method for calculating the inelastic collision term in the electron Boltzmann equation for scattering from a coupled mode system. Useful applications include scattering from plasmon‐polar phonon hybrid modes in modulation doped semiconductor structures. This paper presents numerical methods for including inelastic scattering at momentum‐dependent hybrid phonon frequencies in the low‐field Boltzmann equation for two‐dimensional electrons coupled to bulk phonons. Results for electron mobility in GaAs show that the influence of mode coupling and dynamical screening on electron scattering from polar optical phonons is stronger for two dimensional electrons than was previously found for the three dimensional case.

Electron mobility in GaAs due to piezoelectric scattering

Theoretical studies so far on piezoelectric scattering have resulted in a mobility behaviour of mu approximately T-1/2 in which mu continues to fall indefinitely with increasing temperature T. Such a behaviour cannot tell us where this scattering will become unimportant, as might be expected on physical grounds. The correct behaviour should be a falling curve first, followed by a gradually increasing one when the scattering ceases to be effective. In this work, by using the force-force correlation function technique within the linear response formalism, we obtained a mu versus T curve that shows just this behaviour.

Valence and conduction band molecular-orbital topologies and the optical and electrical properties of gallium arsenide and silicon

Abstract The local electronic valence and conduction band densities of states and corresponding chemical bonding characters of GaAs and silicon are compared on the basis of SCF-X α scattered-wave cluster molecular-orbital computations. The computed densities of states are in good agreement with available spectroscopic data. The calculations indicate that the tops of the valence bands of both materials correspond primarily to nearest-neighbor pσ- and ϱπ-bonding molecular orbitals. However, the molecular-orbital topologies at the bottoms of the conduction bonds of GaAs and silicon are quite different. For GaAs the conduction band edge corresponds to molecular orbitals which are of localized Ga(s, p)As(s, p) σ- and π-antibonding character between nearest neighbors and of delocalized Ga(s)Ga(s) σ-bonding character between second-nearest neighbors. The molecular-orbital topology at the silicon conduction band edge, on the other hand, is of localized Si(s)Si(p) σ-antibonding character between second-nearest neighbors and of localized Si(d)Si(s, p) σ- and π-bonding character between nearest neighbors. These results, in conjunction with Kubo's theory, explain why the electron mobility of GaAs is much larger than that of silicon and why the hole mobilities are similar. This also suggests a “real space” understanding of electron and hole mobility may be related to the localized nature of certain molecular orbitals.

Ionized-impurity scattering due to clusters of correlated impurities.

A theory describing the influence of correlation between impurity positions within impurity clusters on the electron mobility due to ionized-impurity scattering is presented. The theory is applied to calculate the electron mobility in GaAs at a temperature of 77 K in the presence of correlated impurity clusters.

GaAs-Si heterojunction bipolar transistor

A GaAs/Si heterojunction bipolar transistor (HBT) structure is proposed having application for high-frequency operation. The structure combines the high-frequency capability of the GaAs/AlGaAs system with the advanced processing technology of Si. The proposed device consists of an n-AlGaAs/p-GaAs emitter and base layers on an n-Si collector with improved junction characteristics at the GaAs/Si heterointerface afforded by thermal annealing. This novel device structure combines the advantages associated with a wide band-gap AlGaAs emitter, the high electron mobility of GaAs, and the substantial reduction in device parasitics accorded the self-aligned structure. Additionally, the proposed device offers the possibility of planar GaAs processing. With the use of a compact transistor model, calculations of the high-speed capability of this transistor are presented. For an emitter-base junction area of 1 μm×5 μm, optimized fmax=108 GHz and fmax=ft=89 GHz were computed for the GaAs/Si HBT, compared to 76 and 62 GHz, respectively, for equivalent GaAs/AlGaAs HBT’s.

Space-charge-like scattering in epitaxial GaAs from low temperature and high pressure Hall measurements

The Hall electron mobility in GaAs grown by vapor phase epitaxy (VPE), liquid phase epitaxy (LPE), molecular beam epitaxy (MBE), and metalorganic chemical vapor deposition (MOCVD) has been studied both as a function of temperature (77<T<300 K) and hydrostatic pressure (0–8 kbar). The analysis of the data shows that in LPE and VPE crystals, the mobilities are lowered due to space-charge scattering (μSC∝m*−1/2T−1/2) while in MOCVD and MBE samples, a space-charge-like limited mobility (μUN∝m*−nT−1/2) must be included. The value of the exponent n has been found to be 1 for MBE and 2 for MOCVD grown samples. It has been concluded that increasing impurity gradation in these layers is responsible for higher values of n. The pressure coefficient of electron mass in GaAs is determined to be 5.2×10m−4 m*/kbar . The model of central cell scattering due to carbon acceptors fails to account for the experimental data reported in this paper.

Effect of free carrier screening on the electron mobility of GaAs: A study by field-effect measurements

By using a field effect technique, the electron mobility in GaAs at 300K has been studied in two systems where the free electron concentration may be varied over a wide range while the density of ionized impurities is kept constant. These are (a) a thin, almost fully depleted n-type layer on a semi-insulating substrate and (b) a GaAs/AlxGa1−xAs modulation doped heterojunction. In both cases the mobility falls by more than a factor of two as the free electron concentration is reduced, due to loss of screening.

The Effect of Dislocations on the Electron Mobility of GaAs

A relaxation time describing the scattering of electrons by dislocation cores is derived, and utilized in a numerical solution of the Boltzmann transport equation to determine the effect on the drift mobility. From these calculations it is clear that the dislocation scattering is most effective in lightly doped examples, and at low temperatures. At 300 K the drift mobility is practically unaffected for doping levels typical of the active layers of GaAs microwave devices. Es wird eine Relaxationszeit abgeleitet, die die Elektronenstreuung unter Einwirkung von Versetzungskernen beschreibt. Die Boltzmannsche Transportgleichung wird numerisch gelost, um die Auswirkung auf die Driftbeweglichkeit zu bestimmen. Diese Berechnungen zeigen deutlich, das die Versetzungsstreuung besonders stark in schwach dotierten Proben und bei niedrigen Temperaturen auftritt. Bei 300 K bleibt die Driftbeweglichkeit praktisch unbeeinflust, wenn es sich um Dotierungsgrade handelt wie sie bei den aktiven Schichten von GaAs-Mikrowellen-Bauelementen ublich sind.

Comment on ’’Reassessment of space-change and central-cell scattering contributions to GaAs electron mobility’’

Walukiewicz et al.1 have recently stated that previously reported contributions to the electron mobility of GaAs from space-charge and/or central-cell scattering are in fact insignificant, and that reports of a T−1/2 term in the mobility2,3 are artifacts due to the assumption of Mathiessen’s rule. This conclusion is an overstatement of their results and in fact demonstrably incorrect. First, an analysis of the data reported by Stringfellow2 and Stringfellow and Kuenzel3 as well as others has already been performed by Chattopadhyay et al.4 without assuming Mathiessen’s rule. Their conclusion is that central-cell scattering is indeed significant. Second, the particular data analyzed by Walukiewicz et al. are in fact acknowledged in Ref. 2 to have very little T−1/2 scattering. The magnitude of the scattering cross section for T−1/2 scattering, SCA, for other samples is more than an order of magnitude larger, too large to be ascribed to errors inherent in using Mathiessen’s rule. Experimental data convincingly demonstrate this. The mobility versus temperature curves are lower, especially at higher temperatures, for C as opposed to Zn- or Ge-doped samples where all have the same values of ND+NA (see Fig. 2 of Ref. 3). In addition, recently published data5 for MBE GaAs grown with different C doping levels show that for constant ND+NA, SCA is three times larger for the more highly C doped samples. This could not be due to errors inherent in the use of Mathiessen’s rule. For these samples C clearly introduces an increase in the T−1/2 scattering which is not observed for other acceptors. ufc15xr 1W. Walukiewicz, J. Lagowski, and H. C. Gatos, J. Appl. Phys. 52, 5853 (1981). 2G. B. Stringfellow, J. Appl. Phys. 50, 4178 (1979). 3G. B. Stringfellow and H. Kuenzel, J. Appl. Phys. 51, 3254 (1980). 4D. Chattopadhyay, H. J. Queisser, and G. B. Stringfellow, J. Phys. Soc. Jpn. 49, Suppl. A, 293 (1980). 5G. B. Stringfellow, R. Stall, and W. Koschel, Appl. Phys. Lett. 38, 156 (1981). UFTELTAL G. B. Stringfellow G. B. Stringfellow G. B. Stringfellow The T−1/2 term in electron mobility for GaAs and AlxGa1−xAs is shown not to be solely due to errors inherent in the use of Mathiessen’s rule.

Materials for electronic devices

Because of its physical properties silicon is, and probably always will be, the most important semiconducting material. The high-temperature performance and electron mobility of GaAs has obtained a definite position in the marketplace, and the optical and electrical properties of the III–V compounds such as GaInAs are likely to become increasingly important

Temperature dependence of the electron mobility in GaAs

Temperature dependence of the electron mobility in GaAs