Ian Appelbaum

Room-temperature electro-optic up-conversion via internal photoemission

We describe the fabrication and operation of a device which performs linear optical up-conversion at room temperature. The mechanism for up-conversion is based on internal photoemission from a Schottky contact. We then describe the voltage dependence of this device and interpret it in terms of total energy conservation. Although an AlGaAs/GaAs system is employed here, the functionality is not material-specific and therefore should be widely applicable to different materials systems, such as GaN/InGaN.

Near-field scanning optical microscopy as a simultaneous probe of fields and band structure of photonic crystals: A computational study

We demonstrate the feasibility of employing near-field scanning optical microscopy (NSOM) imaging to simultaneously obtain both the eigenfield distribution and the band-structure information of a photonic crystal. We introduce the NSOM measurement configuration required and simulate the imaging process, with both the tip and the sample included, using three-dimensional finite-difference time-domain calculations. Both the field-pattern and the frequency–wave-vector relations of photonic crystal eigenmodes are revealed by analyzing simulated images.

Room-temperature ballistic electron emission luminescence spectroscopy with a scanning tunneling microscope

We present a luminescence spectroscopy for semiconductor heterostructures based on local hot electron injection from a scanning tunneling microscope tip. In addition to a tip voltage bias exceeding the metal-semiconductor Schottky barrier height, this process requires a collector bias voltage to satisfy energy conservation. These results indicate that this method could be used to study local electron transport and simultaneous electroluminescence in buried luminescent layers at depths greater than the ballistic electron mean free path in the collector.

Ballistic electron emission luminescence

We describe the design, fabrication, and operation of a GaAs-based heterostructure device which emits band gap luminescence from solid-state tunnel-junction ballistic injection of electrons with sub-bandgap energy. We find that, due to energy conservation requirements, a collector bias exceeding a threshold determined by the Schottky barrier height and sample band gap energy must be applied for luminescence emission. The consequences of these results for a hybrid scanning-probe microscopy and spectroscopy combining both ballistic electron emission microscopy and scanning tunneling luminescence are emphasized.

Spin-valve photodiode

An optical spin-valve effect is observed using sub-bandgap internal photoemission to generate and collect hot electrons in magnetic multilayers grown on n-Si. Approximately 1.5%-2.5% magnetoresistance is observed in this two-terminal device at low temperature, and this effect is reduced only to 1.1% at room temperature. A simple model is presented to explain the results.

Luminescent spin-valve transistor

A magneto-optical sensor, the luminescent spin-valve transistor, is demonstrated, showing direct control of a light source using a magnetic field. By manipulating the relative magnetizations of thin-film ferromagnets in the transistors base, the luminescence intensity is modulated by approximately 200%.

Avalanche spin-valve transistor

A spin-valve transistor with a GaAs∕AlGaAs avalanche-multiplying collector is demonstrated with >1000% magnetocurrent variation and ≈35× amplification of the collector current. The intrinsic amplification of the magnetic-field sensitive collector current should allow fabrication of spin-valve transistors with high gain in a variety of materials.

Ballistic electron emission luminescence spectroscopy of an InAs quantum dot heterostructure

We present ballistic electron emission luminescence (BEEL) spectroscopy measurements of an InAs quantum dot (QD) heterostructure based on three-terminal hot electron injection using a scanning tunneling microscope (STM) and a planar tunnel-junction transistor. Due to higher injected current, the planar transistors allow us to perform wavelength spectroscopy of the emitted luminescence, which resolves both quantum-confined Stark-shifted QD luminescence near 1.34eV and bulk GaAs luminescence at 1.48eV. This facilitates interpretation of STM BEEL spectra as a function of collector voltage bias. By freezing out the collector leakage current at low temperatures, consistent collector-current spectra are acquired with both STM and planar transistors.

Vertically integrated optics for ballistic electron emission luminescence: Device and microscopy characterizations

By integrating a p-i-n photodiode photodetector directly into a ballistic electron emission luminescence (BEEL) heterostructure with GaAs quantum-well active region, we have obtained a photon detection efficiency of more than 10%. This is many orders of magnitude higher than conventional far-field detection scheme with the most sensitive single-photon counters, enabling BEEL microscopy in systems with no optical components. Detailed analysis shows found a parasitic bipolar injection in parallel with the desired optical coupling between the BEEL heterostructure and the integrated photodiode beyond a characteristic collector bias, which may be solved by improved device design or limiting the operating window of the collector bias. Preliminary BEEL microscopy images of a homogeneous GaAs quantum-well luminescent layer show lateral variations of photon emission correlated with the collector current injection level modulated by surface features or interface defects.

Can silicon dimers form logic gates

We have performed density functional theory calculations to show how a tungsten scanning probe can mediate the interactions between bistable Si(100) surface dimers. Interpreting the state of each dimer as a bit of information, we demonstrate the use of this mediated interaction to construct a NOR logic gate.