A general approach for the performance assessment of nanoscale silicon FETs

Various nonplanar, multigate field-effect transistors (FET) structures have been reported that offer better gate control than planar MOSFETs. In the nanometer regime, however, multigate (nanowire) structures also suffer strong quantum confinement, which causes deleterious effects such as large threshold voltage variation. In this paper, we propose a general approach to compare planar versus nonplanar FETs with the consideration of both electrostatic integrity (gate control) and quantum confinement (the so-called "EQ approach"). With this EQ approach, we show that the cylindrical wire FET and the planar double-gate MOSFET have approximately equal scaling capability for a [001]-oriented wafer, while the nonplanar wire structures are significantly better for other wafer orientations [e.g., (011)] where the effective mass in the confinement direction of the planar MOSFET is relatively small.     

Microwave-signal generation in a planar Gunn diode with radiation exposure taken into account

Microwave-signal generation in planar Gunn diodes with a two-dimensional electron gas, in which we previously studied steady-state electron transport, is theoretically studied. The applicability of a control electrode similar to a field-effect transistor gate to control the parameters of the output diode microwave signal is considered. The results of physical-topological modeling of semiconductor structures with different diode active-region structures, i.e., without a quantum well, with one and two quantum wells separated by a potential barrier, are compared. The calculated results are compared with our previous experimental data on recording Gunn generation in a Schottky-gate field-effect transistor. It is theoretically and experimentally shown that the power of the signal generated by the planar Gunn diode with a quantum well and a control electrode is sufficient to implement monolithic integrated circuits of different functionalities. It is theoretically and experimentally shown that the use of a control electrode on account of the introduction of corrective feedback allows a significant increase in the radiation resistance of a microwave generator with Schottky-gate field-effect transistors.     

Novel single quantum well optoelectronic devices based on exciton bleaching

Novel planar high-speed optoelectronic devices offering advantages for optoelectronic integration are proposed. Exciton-resonant light propagates along a single-mode rib waveguide containing a single quantum well (SQW), the only absorbing medium in the waveguide. The two-dimensional (2D) excitonic optical absorption is controlled by the bleaching effect induced by free carriers, whose electrical conduction simultaneously makes possible optical detection and high-speed transistor action. Three such optical modulating devices are: 1) a gate-controlled single quantum well field-effect transistor (FET) optical modulator (FETOM), 2) an optically-readable memory element, and 3) an optically-switched charge storage device. The FETOM, in which the free-carrier density in the SQW is controlled by the gate voltage, offers high speed (22 ps), small size (125 μm), and unique potential for optoelectronic integration.     

Lateral resonant tunneling transistors employing field-inducedquantum wells and barriers

The authors describe some preliminary experimental results of quantum-effect modulation-doped field-effect transistors (MODFETs) with a variety of nanometer gate geometries. The gate geometries were such that various quantum wells and barriers were formed in the channel of the MODFETs through the field effect imposed by the novel gate structures, and the transport of the electrons was affected by resonant tunneling. The devices were fabricated using a combination of molecular beam epitaxy and electron beam lithography. Electrical measurements of the devices at 4.2 K showed resonant tunneling effects and, in particular, showed that resonant tunneling is more pronounced for a system of quantum wells confined in three dimensions than in two. For these quantum effects to be appreciable at practical temperatures, about 77 K, the feature size of the gate geometries should be smaller than 50 nm     

Resonant tunneling transistors with controllable negative differential resistances

Three-terminal devices based on resonant tunneling through two quantum barriers separated by a quantum well are presented and analyzed theoretically. Each proposed device consists of a resonant tunneling double barrier heterostructure integrated with a Schottky barrier field-effect transistor configuration. The essential feature of these devices is the presence, in their output current-voltage (I_{D} - V_{D}) curves, of negative differential resistances controlled by a gate voltage. Because of the high-speed characteristics associated with tunnel structures, these devices could find applications in tunable millimeter-wave oscillators, negative resistance amplifiers, and high-speed digital circuits.     

Limitations on the performance of field-effect devices for logic applications

The switching time and power dissipation of field-effect devices in integrated logic circuits are obtained using a simple equivalent circuit. It is seen that performance is determined by four basic parameters: channel length, operating voltage, parasitic capacitance, and saturation drift velocity. The effects limiting the optimization of these parameters are examined. It is found that channel length cannot be reduced below about 0.2 µm in the metal-oxide-semiconductor field-effect transistor (MOSFET) or below about 500 Å in the metal-semiconductor field-effect transistor (MESFET). Operating voltages cannot be reduced below about 750 mV due to subthreshold leakage. In the limit of extremely small sizes, the most promising high-speed devices appear to be MESFET structures in GaAs or InP.     

A power junction gate field-effect transistor structure with high blocking gain

A new gate structure is described for vertical-channel power junction gate field-effect transistors (FET's). This gate structure has vertically walled gate regions extending perpendicular to the wafer surface. The structure is fabricated by using orientation-dependent silicon etching and selective vapor-phase epitaxial refill techniques. In comparison to previous gate structures made by planar diffusion, the vertically walled gate structure exhibits one order of magnitude improvement in blocking gain. This improvement in blocking gain has allowed the fabrication of devices having breakdown voltages above 400 V and a current-handling capability of more than 0.5 A with an on-resistance of 12 Ω. The devices are designed to exhibit pentode-like characteristics at low gate voltages and triode-like characteristics at large reverse gate bias voltages in order to obtain the observed high-power handling capability.     

Short-channel GaAs FET fabricated like a MESFET but operating like a JFET

Normally-on GaAs field-effect transistors (FETs) having 1 ?m gate lengths and 4 ?m channel lengths were fabricated in structures grown by molecular beam epitaxy (MBE). The unique part of this device is the very thin p+/n+ structure used to replace the conventional Schottky barriers. The device fabrication procedure is identical to that of a Schottky barrier FET (MESFET), but the devices exhibit characteristics similar to that of a junction field-effect transistor (JFET). This new device, the `camel diode gate FET?, is expected to have applications in both logic and power devices.     

Quantum Dot Gate Three-State and Nonvolatile Memory Field-Effect Transistors Using a ZnS/ZnMgS/ZnS Heteroepitaxial Stack as a Tunnel Insulator on Silicon-on-Insulator Substrates

This paper describes the use of II–VI lattice-matched gate insulators in quantum dot gate three-state and flash nonvolatile memory structures. Using silicon-on-insulator wafers we have fabricated GeO _x -cladded Ge quantum dot (QD) floating gate nonvolatile memory field-effect transistor devices using ZnS-Zn_0.95Mg_0.05S-ZnS tunneling layers. The II–VI heteroepitaxial stack is nearly lattice-matched and is grown using metalorganic chemical vapor deposition on a silicon channel. This stack reduces the interface state density, improving threshold voltage variation, particularly in sub-22-nm devices. Simulations using self-consistent solutions of the Poisson and Schrödinger equations show the transfer of charge to the QD layers in three-state as well as nonvolatile memory cells.     

半导体量子点的器件应用

半导体量子点的生长和性质已成为当今研究的热点。以Ｓ－Ｋ生长模式已成功地生长了无缺陷的半导体量子点。由于其较强的量子效应,量子点结构的光电器件和电子器件有望比量子阱结构的器件具有更好的性能。介绍了量子点在光电器件中的一些应用,包括单电子晶体管、激光器和红外探测器等。     

Electrical and optical properties of self-assembled quantum dots

One of the main directions of contemporary semiconductor physics is the production and study of structures with a dimension less than two, i.e. quantum wires (QWi) and quantum dots (QDs), in order to realise novel devices that make use of low-dimensional confinement effects.One of the promising fabrication methods is to use self-organised three-dimensional (3D) structures, such as 3D coherent islands, which are often formed during the initial stage of heteroepitaxial growth in lattice-mismatched systems. Quantum dots, for example, are believed to provide a promising way for a new generation of optical light sources such as injection lasers. While quantum well structures are already widely used in optoelectronic devices, QWi and QDs appear to be much more difficult to fabricate for this purpose. Some of the electrical and optical properties of self-assembled QDs will be reported in this paper.     

Modulation of absorption in field-effect quantum well structures

Experimental and theoretical investigations of the absorption in a single-modulation-doped quantum well (QW) used as conducting channel of a field-effect transistor are presented. By applying a voltage to the gate, the electron concentration can be varied between 0 and ~10¹² cm^-2. The continuous transition can be optically followed from an undoped to a highly doped QW. Effects of band filling are observed, along with renormalized effects at the first subband edge and electrostatic effects at the higher ones. It is shown that optical techniques can give in situ information on the electron density and temperature as well as on the electrostatic fields inside field-effect structures     

Strained layer heterostructures, and their applications to MODFETs,HBTs, and lasers

Recent developments in strained layer epitaxial systems are reviewed. Their interest stems primarily from the additional degree of freedom that strained layers provide in the design of heterostructures and devices, which has led to device structures that can be tailored to a particular application with, in many cases, performances that are and out of reach with lattice-matched systems alone. With the advent of SiGe alloys, the concept of strained layers was extended to include the elemental semiconductors as well. Si/SiGe heterojunctions have provided a way to study quantum phenomena and explore heterojunction bipolar transistors (HBTs) and field-effect transistors (FETs). In optoelectronics, quantum well lasers with strained InGaAs active layers provide considerable reduced threshold current density. With coherently strained active layers based on GaAs, lasers with longevities superior to those with lattice-matched channels have been obtained     

High-performance 1.5 μm wavelength InGaAs-InGaAsP strainedquantum well lasers and amplifiers

Improved performance of 1.5-μm wavelength lasers and laser amplifiers using strained In_xGa_1-xAs-InGaAsP quantum well devices is reported. The device structures fabricated to study the effects of strained quantum wells on their performance are described. These devices showed TM mode gain, demonstrating the strain-induced heavy-hole-light hole reversal in the valence band. Lasers using these tensile strained quantum wells show higher and narrower gain spectra and laser amplifiers have a higher differential gain compared to compressively strained quantum well devices. Consequently, the tensile strained quantum well lasers show the smallest linewidth enhancement factor α=1.5 (compression α=2.5) and the lowest K-factor of 0.22 ns (compression K=0.58 ns), resulting in an estimated intrinsic 3 dB modulation bandwidth of 40 GHz (compression 15 GHz)     

Analysis of slow-wave transmission lines on multi-layeredsemiconductor structures including conductor loss

Metal lines on semiconductor devices and circuits sometimes show slow-wave phenomena. To determine signal transmission characteristics along the lines, the typical assumption that metal is perfectly conducting is not always valid. A simple and accurate means is used here to include metallic loss in spectral domain analysis of planar transmission lines built on multilayer semiconducting media. Experimental results with a modulation-doped field-effect transistor (MODFET) structure and comparison with the calculations are presented     

Backgating studies inIn0.53Ga0.47As/In0.52Al0.48As modulation-doped field-effect transistors

A study is presented of the backgating effects in normal and inverted modulation-doped field-effect transistors (MODFETs) grown by molecular-beam epitaxy and their dependence on material properties and device geometry. The experiments were performed on devices with 2-μm gate lengths. The effects of both positive and negative (with respect to the source of the experimental devices) voltages applied to both ohmic and Schottky side contacts were investigated. The inverted MODFET structures, which have a very-high-resistance InAlAs buffer layer, showed negligible backgating characteristics up to side-contact voltages as high as 50 V. The normal structures, on the other hand, were very sensitive to the side-contact voltages with essentially a zero threshold voltage     

Optical and electrical properties of nanostructured metal-silicon-metal photodetectors

We report an experimental evaluation of the performance of silicon (Si) photodetectors incorporating one-dimensional (1-D) arrays of rectangular and triangular-shaped nanoscale structures within their active regions. A significant (/spl sim/2/spl times/) enhancement in photoresponse is achieved in these devices across the 400- to 900-nm spectral region due to the modification of optical absorption properties that results from structuring the Si surface on physical optics scales smaller than the wavelength, which both reduces the reflectivity and concentrates the optical field closer to the surface. Both patterned (triangular and rectangular lineshape) and planar Ni-Si back-to-back Schottky barrier metal-semiconductor-metal photodetectors on n-type (/spl sim/5/spl times/10/sup 14/ cm/sup -3/) bulk Si were studied. 1-D /spl sim/50-250-nm linewidth, /spl sim/1000-nm depth, grating structures were fabricated by a combination of interferometric lithography and dry etching. The nanoscale grating structures significantly modify the absorption, reflectance, and transmission characteristics of the semiconductor: air interface. These changes result in improved electrical response leading to increased external quantum efficiency (from /spl sim/44% for planar to /spl sim/81% for structured devices at /spl lambda/=700 nm). In addition, a faster time constant (/spl sim/1700 ps for planar to /spl sim/600 ps for structured at /spl lambda/=900 nm) is achieved by increasing the absorption near the surface where the carriers can be rapidly collected. Experimental quantum efficiency and photocurrents results are compared with a theoretical photocurrent model based on rigorous coupled-wave analysis of nanostructured gratings.     

Field-Effect Chiral Anomaly Devices with Dirac Semimetal

Charge-based field-effect transistors (FETs) greatly suffer from unavoidable carrier scattering and heat dissipation. Analogous to valley degree of freedom in semiconductors, chiral anomaly current in Weyl/Dirac semimetals is theoretically predicted to be nearly nondissipative over long distances, but still lacks experimental ways to efficiently control its transport. Here, field-effect chirality devices are demonstrated with Dirac semimetal PtSe₂, in which its Fermi level is close to the Dirac point in the conduction band owing to intrinsic defects. The chiral anomaly is further corroborated by the planar Hall effect and nonlocal valley transport measurement, which can also be effectively modulated by external fields, showing robust nonlocal valley transport with micrometer diffusion length. Similar to charge-based FETs, the chiral conductivity in PtSe₂ devices can be modulated by electrostatic gating with an ON/OFF ratio of more than 10³. Basic logic functions in the devices are also demonstrated with electric and magnetic fields as input signals.     

MOCVD生长的平面型InGaAs／InP PIN光电探测器件

讨论了采用MOCVD技术生长的平面型InGaAs/InPPIN器件的光学特性及制备工艺。通过引入InP窗口层并制备合适的抗反射膜,大大提高了器件的量子效率,达到～96%,采用平面型结构有可能改善器件的稳定性和可靠性。     

Radiation effects in nanoelectronic elements

Radiation defects induced in planar nanosized structures by steady and pulsed ionizing radiation have been analyzed. Characteristics of test samples with a planar nanosized structure fabricated by deposition of an ultrathin titanium film onto a semi-insulating GaAs substrate and of field-effect transistor structures based on bundles of carbon nanotubes have been studied. Physical mechanisms responsible for the radiation-induced changes in characteristics of the nanoelectronic elements under consideration have been established.