Vertical-cavity electrically driven lasers with three GaInAs
quantum wells and diameters of several μm exhibit room-temperature pulsed current thresholds as low as 1.3mA with 958 nm output wavelength.

Low-Threshold Electrically Pumps Vertical-Cavity Surface-Emitting Microlasers

With the rapid development of technologies for the fabrication of, as well as applications of low-dimensional structures, the demands on characterization techniques increase. Spatial resolution is especially crucial, where techniques for probing the properties of very small volumes, in the extreme case quantum structures, are essential. In this article we review the state-of-the-art in local probe techniques for studying the properties of nanostructures, concentrating on methods involving monitoring the properties related to photon emission. These techniques are sensitive enough to reveal the electronic structure of low-dimensional semiconductor structures and are, therefore, able to give detailed information about the geometrical structure, including fabrication-related inhomogeneities within an ensemble of structures. The local luminescence probe techniques discussed in this review article can be divided into four categories according to the excitation source: (i) spatially localized microphotoluminescence spectroscopy using either strong focusing or masking; (ii) near-field optical microscopy to reach below the diffraction limitation of far-field optics, by either exciting, detecting, or both exciting and detecting in the near field; (iii) cathodoluminescence using focused energetic electrons in an electron microscope; and (iv) scanning tunneling luminescence, using low-energy electrons injected or extracted from the tip of a scanning tunneling microscope.

Local probe techniques for luminescence studies of low-dimensional semiconductor structures

The analysis of photons emitted from the tip–surface region of an STM has produced new information on local dissipative processes in tunneling. A key objective to extend our work to a general spectroscopic and microscopic method is to collect and detect photons as efficiently as possible and here we describe our experimental arrangements, one of which incorporates an ellipsoidal mirror and the other a lens system to collect the photons. The systems operate in UHV and have in situ sample and tip transfer facilities. Examples of a variety of photon spectroscopy modes including photon spectra, isochromat spectra, angular distributions, and photon mapping are presented.

Photon emission scanning tunneling microscope

We consider several fundamental optical phenomena involving single molecules in biased metal-molecule-metal junctions. The molecule is represented by its highest occupied and lowest unoccupied molecular orbitals, and the analysis involves the simultaneous consideration of three coupled fluxes: the electronic current through the molecule, energy flow between the molecule and electron-hole excitations in the leads, and the incident and/or emitted photon flux. Using a unified theoretical approach based on the nonequilibrium Green’s function method we derive expressions for the absorption line shape (not an observable but a useful reference for considering yields of other optical processes) and for the current induced molecular emission in such junctions. We also consider conditions under which resonance radiation can induce electronic current in an unbiased junction. We find that current driven molecular emission and resonant light induced electronic currents in single molecule junctions can be of observable...

/pdf/optical-properties-of-current-carrying-molecular-wires-5hbw1xiodl.pdf

Optical properties of current carrying molecular wires

We have measured the STM (scanning tunneling microscope) light emission spectra of $\mathrm{Au}(110)\ensuremath{-}(2\ifmmode\times\else\texttimes\fi{}1)$ at 80 K with atomic spatial resolution. The individual Au atoms along the $(2\ifmmode\times\else\texttimes\fi{}1)$ rows could be resolved in the STM image. Distinctly different emission spectra are observed depending on whether the tip is located over the atomic row or over the valley between the rows. The spectrum obtained over the row atoms can be ascribed to the emission by localized surface plasmons. The spectrum found over the valley contains emission from excitations atomically localized in the valley.

Scanning Tunneling Microscope Light Emission Spectra of Au ( 110 ) − ( 2 × 1 ) with Atomic Spatial Resolution

In a scanning tunneling microscope experiment, the luminescence induced by the recombination of holes with electrons tunneling into cleaved (110) GaAs/AlGaAs heterostructures is used to image the interface region with nanometer resolution.

Nanometer resolution in luminescence microscopy of III-V heterostructures

Using electroluminescence associated with scanning tunneling microscope in AlxGa1−xAs heterostructures, we show that: (a) luminescence due to recombination can be induced within single quantum wells of dimensions down to a few nm and can also be used to image them, (b) the energy of bulk bands can be determined, and (c) transport parameters can be measured, e.g., the thermalization length and the diffusion length of minority electrons. This technique opens up new possibilities for the study and characterization of semiconductors and devices—including the possibility of studying surface states and single trapping centers associated with lattice defects, impurities, chemisorbed species, etc.

Luminescence in scanning tunneling microscopy on III–V nanostructures

The tip of a scanning tunneling microscope is used as a source of ultralow-energy electrons to excite luminescence in model AlGaAs/GaAs(001) heterostructures. This beam injection technique has the advantage of providing a nanometer-sized charge generation volume. We demonstrate the application of this technique to determine minority charge carrier transport parameters such as the thermalization length of hot electrons and the diffusion length of minority electrons.

/pdf/high-resolution-electron-beam-injection-in-semiconductors-qn6wbigwg8.pdf

High-resolution electron-beam injection in semiconductors using a scanning tunneling microscope

STM and luminescence

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Nanometer resolution in luminescence microscopy of III-V heterostructures

Luminescence in scanning tunneling microscopy on III–V nanostructures

High-resolution electron-beam injection in semiconductors using a scanning tunneling microscope

STM and luminescence