Low-density spin susceptibility and effective mass of mobile electrons in Si inversion layers

We studied the Shubnikov-de Haas (SdH) oscillations in high-mobility Si-MOS samples over a wide range of carrier densities n approximately (1-50)x10(11) cm(-2), which includes the vicinity of the apparent metal-insulator transition in two dimensions (2D MIT). Using a novel technique of measuring the SdH oscillations in superimposed and independently controlled parallel and perpendicular magnetic fields, we determined the spin susceptibility chi(*), the effective mass m(*), and the g(*) factor for mobile electrons. These quantities increase gradually with decreasing density; near the 2D MIT, we observed enhancement of chi(*) by a factor of approximately 4.7.     

Search for excited and exotic electrons in the egamma decay channel in pp collisions at sqrt[s] = 1.96 TeV

We present a search for excited and exotic electrons (e(*)) decaying to an electron and a photon, both with high transverse momentum. We use 202 pb(-1) of data collected in pp collisions at sqrt[s] = 1.96 TeV with the Collider Detector at Fermilab II detector. No signal above standard model expectation is seen for associated ee(*) production. We discuss the e(*) sensitivity in the parameter space of the excited electron mass M(e(*)) and the compositeness energy scale Lambda. In the contact interaction model, we exclude 132 GeV/c(2)相似文献   

Demonstration of a 1/4-cycle phase shift in the radiation-induced oscillatory magnetoresistance in GaAs/AlGaAs devices

We examine the phase and the period of the radiation-induced oscillatory magnetoresistance in GaAs/AlGaAs devices utilizing in situ magnetic field calibration by electron spin resonance of diphenyl-picryl-hydrazal. The results confirm a f-independent 1/4-cycle phase shift with respect to the hf=j variant Planck's over 2pi omega(c) condition for j>/=1, and they also suggest a small ( approximately 2%) reduction in the effective mass ratio, m(*)/m, with respect to the standard value for GaAs/AlGaAs devices.     

Connecting the reentrant insulating phase and the zero-field metal-insulator transition in a 2D hole system

We present the transport and capacitance measurements of 10 nm wide GaAs quantum wells with hole densities around the critical point of the 2D metal-insulator transition (critical density p(c) down to 0.8 × 10(10)/cm2, r(s) ～ 36). For metallic hole density p(c) < p < p(c) + 0.15 × 10(10)/cm2, a reentrant insulating phase (RIP) is observed between the ν = 1 quantum Hall state and the zero-field metallic state and it is attributed to the formation of pinned Wigner crystal. Through studying the evolution of the RIP versus 2D hole density, we show that the RIP is incompressible and continuously connected to the zero-field insulator, suggesting a similar origin for these two phases.     

Resistance noise scaling in a dilute two-dimensional hole system in GaAs

We have measured the resistance noise of a two-dimensional (2D) hole system in a high mobility GaAs quantum well, around the 2D metal-insulator transition (MIT) at zero magnetic field. The normalized noise power S(R)/R(2) increases strongly when the hole density p(s) is decreased, increases slightly with temperature (T) at the largest densities, and decreases strongly with T at low p(s). The noise scales with the resistance, S(R)/R(2) approximately R2.4, as for a second order phase transition such as a percolation transition. The p(s) dependence of the conductivity is consistent with a critical behavior for such a transition, near a density p(*) which is lower than the observed MIT critical density p(c).     

Relaxation length of a polymer chain in a quenched disordered medium

Using Monte Carlo simulations, we study the relaxation and short-time diffusion of polymer chains in two-dimensional periodic arrays of obstacles with random point defects. The displacement of the center of mass follows the anomalous scaling law r(c.m.)(t)(2)=4D(*)t(beta), with beta<1, for times t相似文献   

Spin polarization dependence of carrier effective mass in semiconductor structures: spintronic effective mass

We introduce the concept of a spintronic effective mass for spin-polarized carriers in semiconductor structures, which arises from the strong spin-polarization dependence of the renormalized effective mass in an interacting spin-polarized electron system. The majority-spin many-body effective mass renormalization differs by more than a factor of 2 at r(s) = 5 between the unpolarized and the fully polarized two-dimensional system, whereas the polarization dependence (approximately 15%) is more modest in three dimensions around metallic densities (r(s) approximately 5). The spin-polarization dependence of the carrier effective mass is of significance in various spintronic applications.     

Small-signal modulation characteristics for 1.5 μm lattice-matched InGaNAs/GaAs and InGaAs/InP quantum well lasers

The small-signal modulation characteristics of 1.5 m lattice-matched InGaNAs/GaAs and InGaAs/InP quantum well lasers and their temperature dependence have been calculated. It is found that the maximum bandwidth of the InGaNAs/GaAs quantum well lasers is about 2.3 times larger than that of the InGaAs/InP quantum well lasers due to the high differential gain which results from the large electron effective mass in the dilute nitride system. The slope efficiency for the 3 dB bandwidth as a function of optical density is twice as large for InGaNAs/GaAs as for InGaAs/InP quantum well lasers.     

Microwave-Induced Magneto-Intersubband Scattering in a Square Lattice of Antidots

JETP Letters - The effect of microwave radiation on low-temperature electron magnetotransport in a square antidot lattice with a period of d ≈ 0.8 µm based on a GaAs quantum well with...     

GaAs(111)A/B surface orientation effects on electron density in normal and inverted pseudomorphic HEMTs

We present calculations of the two-dimensional electron density in a Si -doped AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor (P-HEMT), at low temperature, for three different growth directions (001) and (111)A/B. The calculations are made using a self-consistent resolution of Schrödinger and Poisson equations. The presence of a strong built-in piezoelectric field in (111)A/B growth directions causes changes of the confining potential shape and the carrier distribution in the InGaAs channel. We discuss the influence of GaAs substrate orientation on the conduction-band structure and thereafter on the two-dimensional electron gas (2DEG) concentration in the channel. Our results show that the calculated 2DEG concentration in the normal P-HEMT structure grown on a (111)A GaAs substrate is significantly higher than those grown on (001) and (111)B GaAs substrates. We also note an increase of the average separation between the ionized donors and the carriers. On the other hand, the GaAs (111)B substrate orientation appears as inadequate for the type of structure (normal P-HEMT) on account of the charge-transfer reduction in the channel compared with the (001) orientation. In contrast, we demonstrate that the calculated 2DEG Si -doped GaAs/InGaAs/AlGaAs pseudomorphic inverted high electron mobility transistor (PI-HEMT) grown on aGaAs (111)B substrate is appreciably higher than that grown on (001) and afterwards an enhancement of the spatial separation between confined electrons in the channel and ionized dopants occurs. These effects might result in considerably improved devices of great interest regarding high electron mobility. PACS 73.20.Dx; 73.20.At; 73.90.+f; 73.63.Hs; 72.20.Dp     

Two groups of misfit dislocations in GaAs on Si

High-resolution cross-sectional and conventional plan-view transmission electron microscope observations have been carried out for molecular beam epitaxially grown GaAs films on vicinal Si (001) before and after annealing as a function of film thicknesses and observation directions between two orthogonal 110 directions. Two groups of misfit dislocations are characterized at the interface regions between GaAs and Si by analyzing whether their extra half planes exist in the film or the substrate side. Group I misfit dislocations due to stress caused by a lattice misfit between GaAs and Si consist of partial dislocations and 60° and 90° complete dislocations in an as-grown state. With an increase in the film thickness, partial dislocations decrease and complete dislocations increase. After annealing, partial dislocations almost completely disappear and 90° perfect dislocations are predominantly observed. Group II misfit dislocations due to thermal-expansion misfit-induced stress are all 60°-type complete dislocations regardless of film thicknesses and annealing treatment.On leave from Central Research Laboratory, Hitachi, Ltd., Tokyo 185, Japan     

Electron mass in dilute nitrides and its anomalous dependence on hydrostatic pressure

The dependence of the electron mass on hydrostatic pressure P in N-diluted GaAs1-xNx (x=0.10% and 0.21%) is investigated by magnetophotoluminescence. Exceedingly large fluctuations (up to 60%/kbar) in the electron mass with increasing P are found. These originate from a pressure-driven tuning of the hybridization degree between the conduction band minimum and specific nitrogen-related states. Present results suggest a hierarchy between different nitrogen complexes as regards the extent of the perturbation these complexes exert on the electronic properties of the GaAs host.     

Surfactant-mediated molecular beam epitaxy of high-quality (111)B-GaAs

We present a novel approach to the molecular beam epitaxy of [111]-oriented GaAs. Surface-segregating In employed as an isoelectronic surfactant allows us to achieve mirror-like (111) GaAs surfaces within a wide range of growth conditions. Scanning electron and atomic force microscopy confirm the excellent morphology of the resulting samples. High-resolution X-ray diffraction shows the incorporation of In into the films to be negligible. Finally, we demonstrate a 10 Å-In_0.2Ga_0.8As/300 Å-GaAs superlattice based on surfactant-grown GaAs with a photoluminescence linewidth as narrow as 4.2 meV.     

In0.2Ga0.8As/GaAs interface revealed by an AlAs marker layer

A detailed analysis of the microstructure of layered semiconductor heterostructures is only possible if the interface between the various layers can be accurately located. Microstructural features whose characterisation is dependent on the location of the interface include the planarity and width of the layers, the composition profile and the geometry of misfit dislocations (in the particular case of lattice mismatched heterostructures). We report on an investigation to image, at high resolution in the transmission electron microscope, the interface in an In_0.2Ga_0.8As/GaAs structure grown by molecular beam epitaxy. The difficulty in locating the interface, due to similarity in electron optical behaviour of GaAs and In_0.2Ga_0.8As when imaged in a 110 direction, was overcome by incorporating into the structure a marker layer of AlAs two unit cells thick (11.4 Å in total) between the GaAs and the In_0.2Ga_0.8As layers. Lattice fringe images of an In_0.2Ga_0.8As/AlAs/GaAs structure are presented which show, at near atomic resolution, the location of the misfit dislocations relative to the In_0.2Ga_0.8As/GaAs interface.     

Terahertz time-domain magnetospectroscopy of a high-mobility two-dimensional electron gas

We have observed cyclotron resonance in a high-mobility GaAs/AlGaAs two-dimensional electron gas by using the techniques of terahertz time-domain spectroscopy combined with magnetic fields. From this, we calculate the real and imaginary parts of the diagonal elements of the magnetoconductivity tensor, which in turn allows us to extract the concentration, effective mass, and scattering time of the electrons in the sample. We demonstrate the utility of ultrafast terahertz spectroscopy, which can recover the true linewidth of cyclotron resonance in a high-mobility (>10(6) cm(2)V(-1)s(-1)) sample without being affected by the saturation effect.     

Microprobe photoluminescence measurement on heteroepitaxial GaAs on Si grown by metalorganic chemical vapor deposition

Microprobe photoluminescence (PL) measurements at 77 K were used to study the effect of the GaAs layer thickness on optical quality and variations in strain in GaAs/Si containing microcracks. PL peak intensities increase with the increase in thickness of GaAs layers and the peak intensity for the 5.5 m GaAs layer was a factor of 20 higher than those for the 1–2 m GaAs layers. Spatial nonuniformities in strain in the vicinity of two microcracks reveal that stress was almost released at the intersection of two microcracks and is maximum half way between two microcracks.On leave from Semiconductor Materials Lab., Korea Institute of Science and Technology (KIST)     

ZnS thin films grown by atomic layer deposition on GaAs and HgCdTe substrates at very low temperature

ZnS films grown on GaAs and HgCdTe substrates by atomic layer deposition (ALD) under very low temperature were investigated in this work. ZnS films were grown under several temperatures lower than 140 °C. The properties of the films were investigated with high-resolution X-ray diffraction (HRXRD), scanning electron microscope (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The results showed the ZnS films were polycrystalline. The growth rate monotonically decreased with temperature, as well as the root mean square (r.m.s) roughness measured by AFM. XPS measurement revealed the films were stoichiometric in Zn and S.     

Heterogeneous integration of GaAs pHEMT and Si CMOS on the same chip

In this work,we demonstrate the technology of wafer-scale transistor-level heterogeneous integration of Ga As pseudomorphic high electron mobility transistors(p HEMTs) and Si complementary metal–oxide semiconductor(CMOS) on the same Silicon substrate.Ga As p HEMTs are vertical stacked at the top of the Si CMOS wafer using a wafer bonding technique,and the best alignment accuracy of 5 μm is obtained.As a circuit example,a wide band Ga As digital controlled switch is fabricated,which features the technologies of a digital control circuit in Si CMOS and a switch circuit in Ga As p HEMT,15% smaller than the area of normal Ga As and Si CMOS circuits.     

Selective deposition of Au films on GaAs by projection-patterned excimer laser doping combined with electroless plating

Resistless microfabrication of Au thin films on n-type GaAs by projection-patterned laser doping using a KrF excimer laser and a 10% SiH₄-He gas is described. Gold thin films with a linewidth as narrow as 1.57 m are deposited selectively on the doped regions by electroless plating in a commercial Au-24s aqueous solution. The isotropic growth of the deposited films is discussed by comparing the linewidth of the deposited films with that of the doped regions. Furthermore, the dependence of the deposition characteristics of Au thin films on the laser irradiation conditions is investigated.Presented at LASERION '91, June 12–14, 1991, München (Germany)     

Silicon doping effects on optical properties of InAs ultrathin layer embedded in GaAs/AlGaAs:δSi high electron mobility transistors structures

Micro-Raman scattering measurements were used to study the silicon delta-doped layer density variation effect on InAs ultrathin layer embedded in silicon-delta-doped GaAs/AlGaAs high electron mobility transistors (HEMTs) structures properties. These structures were grown by molecular beam epitaxy on GaAs substrates with different silicon (Si) delta-doped layer densities. Two coupled plasmon–longitudinal optical (LO) phonon modes (L− and L+) were observed in the micro-Raman spectra of the Si-delta-doped samples, and both their wave numbers and intensities were dependent on the silicon delta-doped layer density. There is evidence to suggest that the increase of the Si doping level results in the increase of exciton–phonon scattering which is mainly due to the incorporation of Si and the increase of the two-dimensional electron gas (2DEG) in the InAs/GaAs interface. From fitting the temperature-dependence of full width at half maximum (FWHM) of quantum well’s photoluminescence peak (P₁) by the exciton–photon coupling model, it was found that the interaction between exciton and phonon in Si-delta-doped quantum wells was higher than that in the undoped sample. This result was confirmed as resulting from the increase of plasmon–phonon scattering which is attributed to the increase of free carriers donated from implanted Si dopant. The self-consistent Poisson–Schrödinger model calculation results are in good agreement with the experimental results, where the 2DEG densities increase linearly with increasing the Si-delta-doped layer density.