Atomic Force Microscopy (AFM) measurements have been performed for Fe doped SrTiO 3 thin films with an Fe concentration of 2 and 5 at%. Thin films with a thickness of about 20 nm were grown by pulsed laser deposition on single crystalline SrTi 0.99 Nb 0.01 O 3 substrates. Low-energy electron diffraction examination showed that the films are single crystalline. The regions treated with the AFM tip (applied dc voltage up to 6V) showed inhomogeneity of the electrical conductivity.
Using magnetotransport measurements we have investigated the electrical properties of 3 nm wide lattice-matched InGaAs/InP quantum wells grown by metalorganic vapour phase epitaxy. We observe a significant persistent photoconductivity (PPC) effect even at room temperature. The energetic parameters of the deep level which we believe to be connected with the PPC have been determined from the variation with photon energy and from the temperature-dependent relaxation. The PPC permits the study of transport parameters as a function of the electron density. In this way, the density dependences of the in-plane effective mass and of the ratio of quantum to classical scattering times have been derived from Shubnikov - de Haas oscillations. The low-field Hall effect measurements yield peculiar anomalies in the mobility versus density curves at 77 K when evaluated on the basis of a one-band model. We show that these anomalies are caused by a second channel which can be filled with a limited number of carriers.
For the application of InGaAs/InP devices for high-speed electronics and optoelectronics in the near infrared, the quality of the InGaAs/InP interfaces is of crucial importance. However, during growth a number of different intermixing effects may occur due to the switching of the group-III as well as the group-V elements at each interface. Raman spectroscopy is applied on InGaAs/InP multi quantum wells (MQWs) for the identification of possible ternary and quaternary interface layers from their characteristic lattice vibration frequencies. E.g. at the InGaAs-to-InP interfaces quaternary InGaAsP layers are detected. A variation of the gas switching sequence at the interfaces strongly affects the interface-layer signals. Thus, our analysis allows the optimization of the growth process. The optimization results in the occurrence of confined optical phonons from the InGaAs quantum well layers in the Raman spectrum for sufficiently abrupt interfaces. Besides, very narrow acoustic phonon peaks are observed. This indicates that the thickness of the InGaAs and InP slabs is highly regular over the whole stack. Für die Anwendung von InGaAs/InP Bauelementen in der Hochfrequenzelektronik und Opto-elektronik im nahen Infrarot ist die Qualität der InGaAs/InP Grenzflächen von wesentlicher Bedeutung. Hier können jedoch beim Wachstum verschiedene Durchmischungen auftreten, weil an jeder Grenzfläche sowohl die Gruppe-III als auch die Gruppe-V Elemente gewechselt werden. An InGaAs/InP Vielfachquantentöpfen wird Ramanspektroskopie eingesetzt, um eventuelle ternäre und quaternäre Grenzschichten anhand ihrer charakteristischen Gitterschwingungen nachzuweisen. Zum Beispiel zeigen sich an den InGaAs-zu-InP Grenzflächen quaternäre InGaAsP Schichten. Durch eine systematische Variation der Gaswechselparameter lassen sich die Grenzschichtdicken stark beeinflussen. So kann man mit Hilfe dieser Analyse den Wachstumsprozeß optimieren. Dies führt zum Erscheinen von confined optischen Phononen der InGaAs-Schichten im Ramanspektrum für hinreichend scharfe Grenzflächen. Ebenfalls zeigen sich sehr schmale Peaks von gefalteten akustischen Phononen. Dies bedeutet, daß die Dicken der einzelnen InGaAs und InP Schichten über die gesamte Abfolge sehr regelmäßig sind.
The p+ -cap layer was used to fabricate a metal-semiconductor-metal (MSM) interdigitated photodetector on Ga0.47In0.53As. The measured barrier height was, ΦBn = 0.52 V, the ideality factor n = 1.1 and average dark current density 2mA/cm2. A rise time of 45 ps at λ = 1.3μm under 2 V bias was measured for an MSM photodiode with 3μm finger width and finger gaps and an active area of 100 × 100μm2.
The transport properties of three p-type modulation-doped InxGa1−xAs/InP (0.73≤x≤0.82) single-quantum-well structures grown by metalorganic chemical-vapor deposition are reported. High carrier mobilities of μH=7800 cm2/V s coupled with total carrier concentrations of pS=2.1×1012 cm−2 were reached, for example, for x=0.73 at 5 K. Shubnikov–de Haas and quantum Hall-effect measurements at 50 mK showed the population of two spin-split V3/2 subbands. Using p-modulation-doped field-effect transistors with a gate length of LG=1 μm, fabricated on the same samples, the carrier transport at moderate and high fields was investigated at 77 K. Thereby, the population of the heavy-hole subband and, above a critical field, also the occupation of the light-hole subband were verified. With the help of dc transconductance (gmext-VGS) and magnetotransconductance measurements a decoupling between both subbands at cryogenic conditions and moderate fields was observed, resulting in two clearly defined conducting channels. Further analysis of the measured mobility-voltage (μ-VGS) and velocity-field (vavg-Eavg) profiles revealed that carrier transport in compressively strained two-dimensional hole gas (2DHG) systems is strongly affected by intersubband scattering and shows a nonlinear behavior at low fields, caused by the zone-center degeneracy of their E-k∥ distribution.
In-plane effective masses m*∥ and quantum scattering times are derived from temperature-dependent Shubnikov–de Haas oscillations measured on a series of modulation-doped InxGa1−xAs/InP quantum wells with x=0.53 and 0.75, and for well widths ranging from 3 to 7 nm. The values for m*∥ are consistently higher by 30%–70% than the respective bulk data. This result is in good agreement with recent theoretical calculations which predict an increase of m*∥ with decreasing well width. The scatter of the mass values for nominally identical quantum wells is assumed to reflect corresponding variations of the well widths. The ratio of quantum to classical scattering times and the carrier density dependence of the electron mobilities indicate that Coulomb scattering is important even in extremely narrow quantum wells.
InP/InGaAs is a powerful material system for a variety of devices including HFETs. The quality of the heterointerface is very sensitive to growth parameters, especially to the switching sequence of the reactive gases. Improvement of the interface with respect to electron transport was achieved by growth interruptions without group-V stabilization of the surface before growth of the subsequent layer is started.< >
This chapter contains five sections related to advances in technology and characterization. The first section investigates influence of Ti top electrodes on the oxidation state of epi-taxially grown STO thin films and the corresponding resistive switching devices. The second section shows comparison of work diode- and CO2-laser heater versions. The third section reviews the influence of ALD processing and different top electrodes on the structural, morphological and electrical properties of ZrO2. The fourth section views the resistance switching characteristic of Nb2O5 thin films integrated into Pt/Nb2O5/Ti/Pt micro cross bar structures on Si/SiO2 substrates. The fifth section considers the investigations of CDW in Dy5Ir4Si10 at different temperatures using transmission electron microscopy (TEM) techniques including electron diffraction and dark-field imaging. Controlled Vocabulary Terms electron diffraction; switching; thin films; transmission electron microscopy
