August 2015 Vol. 13 No. 8

Feature Articles: Frontier Research on Low-dimensional Semiconductor Physics

• Ultimate Control of Electronic Properties in Low-dimensional Semiconductors

  

  Abstract
  Recent progress in semiconductor technology has enabled the development of structures that are scaled down to the nanometer level with high precision by using highly sophisticated nanofabrication and crystal growth techniques. Confining electrons to such low-dimensional nanostructures makes it possible to achieve precise control of electrons as particles as well as waves. The Feature Articles in this issue review our recent research activities involving low-dimensional semiconductor devices that will be applied to achieve innovative electronics in future science and information and communication technologies.

• High-speed Single-electron Transfer toward High-accuracy Current Standards

  

  Abstract
  Single-electron transfer is a technique for manipulating single electrons to generate an accurate electric current, which is expected to be used as a new current standard. Realization of the current standard is important for performing quantum metrology triangle experiments, with which we can confirm the accuracy of fundamental physical constants, and it could be a contributing factor in redefining the ampere. NTT Basic Research Laboratories has been studying single-electron transfer using silicon transistors. In this article, we discuss high-speed single-electron transfer via a small island electrically formed using silicon transistors and via a trap level in silicon.

• Noise in Nanometer-scale Electronic Devices

  

  Abstract
  Downsizing electronic devices in integrated circuits increases the noise-related degradation of circuit performance, and thus, it is becoming more important to analyze noise with single-electron resolution. We discuss here the use of a nanometer-scale transistor and capacitor in analyzing thermal noise, one of the most fundamental types of noise in electronic devices, with single-electron resolution. When the capacitor size is substantially reduced, the well-known model of thermal noise is no longer valid, and voltage noise is squeezed.

• Gate Tuning of Direct/Indirect Optical Transitions in Silicon

  

  Abstract
  Silicon is one of the most important semiconductor materials in microelectronics and is known as a typical indirect bandgap semiconductor. In these semiconductors, the minimal energy state in the conduction band and the maximal energy state in the valence band appear at different momenta. This makes it difficult to obtain efficient light emission. In this article, we present a means of electrically tuning the direct/indirect optical transitions using a specially prepared Si/SiO₂ interface, where anomalously large valley splitting appears. This tunability is achieved by utilizing the close relationship between valley splitting and a direct optical transition in silicon and its proportional relationship with respect to a gate electric field.

• Microscopic Probing of Crystalline Electrons Using Magnetic Resonance

  

  Abstract
  Electrons in semiconductors are often referred to as free electrons, meaning that they can move freely. They are also spatially extended like a wave. On the other hand, electrons are negatively charged particles and thus repel each other. Theory predicts that at low temperatures and in high magnetic fields, electrons―in an effort to maintain a distance from one another―organize themselves. They form a regular array like the atoms in a crystal, a state known as the Wigner crystal. This article describes experiments that exploit nuclear magnetic resonance (NMR) to probe the microscopic structure of a Wigner crystal. These experiments demonstrate the capability of NMR to resolve the spatial variation of electron waves on the nanometer scale.

• Semiconductor Quantum Structures with Single-atom Precision

  

  Abstract
  Atom manipulation is a technology to assemble microstructures atom-by-atom by controlling the number of component atoms and their configuration. Combining this technology with the epitaxial growth of high quality semiconductor crystals makes it possible to uniformly manufacture and integrate quantum structures with single-atom precision. This technological innovation is expected to enable the next generation of electronics to overcome the limits of conventional silicon technology. In this article, atom manipulation of quantum structures at a compound semiconductor surface is reviewed, and a typical example is described―the fabrication of an ultimately precise quantum dot and quantum dot molecules.

• Creating a Topological Insulator Using Semiconductor Heterostructures

  

  Abstract
  Topological insulators are new states of matter that cannot be classified into any existing categories of materials. They have attracted much attention for their potential use in electronic and quantum computing devices because of their specific electron transport properties. In this article, we describe how we created an artificial topological insulator using a heterostructure comprising common semiconductor materials.

Regular Articles

• Two-mode Squeezing in an Electromechanical Resonator

  

  Abstract
  A mechanical resonator integrated with piezoelectric transducers enables mechanical nonlinearities to be dynamically engineered to emulate non-degenerate parametric down-conversion. In this configuration, millions of phonons are simultaneously generated in pairs in two macroscopic vibration modes, which results in the amplification of their motion by more than 20 dB. Mechanical two-mode squeezed states are also created in parallel, which exhibit fluctuations 5 dB below the thermal level of their constituent modes and they harbor correlations between the modes that become perfect as their amplification is increased. This remarkable observation of correlations between two massive phonon ensembles establishes the means to create an entangled macroscopic mechanical system at the single phonon level.

• Improving User Capacity and Disaster Recovery Time in IP Telephone Service Systems

  

  Abstract
  The NTT Group is working on improving Internet protocol (IP) telephone networks and solving certain problems associated with them. Specifically, efforts are underway to improve the accommodation rate, reduce network operating costs when the number of network users increases, and reduce service recovery time when a network is damaged because of a natural disaster. To resolve these problems, we developed a system architecture that simplifies the operation of IP telephone networks and uses network equipment much more efficiently. This is possible with a subscriber data management server. We describe here our new network architecture, the mechanism to solve these problems, and the effect it has on IP telephone networks.

• Development of High-capacity Protocol for M2M Services and Its Application to a Pallet Management System

  

  Abstract
  NTT Network Innovation Laboratories has developed a high-capacity protocol for the 920-MHz band in order to enhance the effectiveness and accelerate the adoption of machine-to-machine (M2M) services. This protocol can detect the movement of hundreds of terminals and manage more than 10,000 terminals. The protocol is applied to physical distribution systems in which very large inventories need to be controlled. It offers efficient management of loading/unloading activities. The protocol was commercialized as a pallet management system in fiscal year 2015. In this article, we describe the protocol and explain how we verified its performance in tests conducted in an actual goods distribution center.

Global Standardization Activities

• Reports of 4th ITU-T Review Committee and 1st FG-DFS (Digital Financial Services) Meetings

  

  Abstract
  Agreement was reached in the ITU-T (International Telecommunication Union, Telecommunication Standardization Sector) to establish a Review Committee (RevCom) to discuss a new standardization structure for the next study period starting in 2017. This agreement occurred at the WTSA (World Telecommunication Standardization Assembly) held in 2012. Additionally, it was agreed to establish a new Focus Group on Digital Financial Services (FG-DFS) at the TSAG (Telecommunication Standardization Advisory Group) meeting held in June 2014. This article reports on the key topics discussed at two meetings of these committees, the fourth meeting of RevCom, held in Tunis, Tunisia, in January 2015, and the first meeting of FG-DFS, held in Geneva, Switzerland, in December 2014.

Practical Field Information about Telecommunication Technologies

• Case Studies of Faults and Countermeasures in Access Telephone Office

  

  Abstract
  This article reports on recent faults in optical access communication facilities that occurred in a telephone office. We review (1) a communication facilities problem caused by removal of a LAN (local area network) cable, (2) an accidental cable breakage that occurred while fixing cables on a distribution frame, and (3) a service interruption that occurred due to deterioration of an optical branch module used for testing optical lines. Cases (1) and (2) involved breakdowns that occurred during construction, whereas case (3) was an unforeseen breakdown related to long-term deterioration. We also present the appropriate countermeasures to these faults that were applied in order to maintain continuous operation of the communication facilities. This article is the thirtieth in a bimonthly series on practical field information on telecommunication technologies. This month’s contribution is from the Access Engineering Group, Technical Assistance and Support Center, Maintenance and Service Operations Department, Network Business Headquarters, NTT EAST.

External Awards/Papers Published in Technical Journals and Conference Proceedings

• External Awards/Papers Published in Technical Journals and Conference Proceedings