A. S. Karakashian

Angular scan spectrum of a surface plasma excitation on a Schottky diode

Abstract The reflectivity and quantum efficiency response functions of a Schottky-barrier diode are measured in an angular scan attenuated total reflection experiment. The excitation of the surface plasma resonance is observed in both of these response functions. Improvements in the quantum efficiency of the diodes over the normal incidence case by factors of from 1.5 to 11.5 are obtained when the surface plasma resonance is excited.

Phonon mediated lifetimes in intersubband terahertz lasers

We present a detailed study of the electron-LO phonon interaction in a triple quantum well structure, which acts as the active region in an intersubband terahertz emitter. The phonon modes of the heterostructure were calculated using a transfer matrix method within the framework of the dielectric continuum model. Unlike earlier calculations that approximate phonon emission rates using bulk-like phonon modes, we exploit the presence of specific interface and layer-confined phonon modes. The electronic levels are designed to be in resonance with one of the phonon modes for optimizing phonon-scattering rates and to enhance device performance. Our calculations indicate that it is beneficial to utilize the higher energy interface phonon modes rather than the confined phonon modes for faster depopulation in a three level lasing scheme. Scattering rates for two different designs were computed to establish the above result.

Radiation-induced carbon-related defects in p-type silicon

The production and removal of carbon‐related defects have been investigated in 1‐MeV electron‐irradiated boron‐doped silicon solar cells using deep level transient spectroscopy (DLTS). In Czochralski (CZ) material, the interstitial carbon defect (hole trap at Ev+0.27 eV), CI, decays by thermal and charge injection processes. We find that irradiation by MeV electrons creates CI while simultaneously removing it through the minority‐carrier injection process. Removal of CI correlates with significant growth in the density of a complex reportedly consisting of carbon and oxygen (hole trap at Ev+0.38 eV). Thermal annealing produces a different DLTS signal than does minority‐carrier injection indicating that the carbon and oxygen complex (C+O) is at least two species. The effective cross section for minority‐carrier‐induced annealing of CI is found to be 2×10−18 cm2 in these samples.

A model calculation for surface plasma-enhanced internal photoemission in Schottky-barrier photodiodes

Attenuated total reflection is commonly used to excite the surface plasma wave (SPW) on a metal film. The SPW traveling on the surface of the metal will enhance the emission of photoelectrons from the metal into the semiconducting region of a Schottky barrier photodiode. A model consisting of an aluminum film on n‐type gallium arsenide forming a Schottky barrier photodiode is used to predict the enhanced emission of photoelectrons over the barrier between the aluminum film and the gallium arsenide. The quantum efficiency for this model shows a strong dependence on parameters such as the electron escape depth, film thickness, and the spacer thickness between the prism coupler and the photodiode. The model proved to be effective when used to fit quantum efficiency and reflectivity data resulting from an angle scan experiment.

Observation of negative differential resistance in GaAlAs single-barrier heterostructure at room temperature

Observation of experimental negative differential resistance at room temperature due to electron tunneling in a multiple-step single-barrier GaAlAs heterostructure is reported. Theoretical investigations of a three-step single-barrier heterostructure were conducted using the transfer matrix method and the Tsu–Esaki approach to obtain the transmission coefficients and current–voltage characteristic, respectively. The system was designed based on these calculations, and grown with molecular beam epitaxy. The diode exhibited negative differential resistance at 300 K and had a peak-to-valley current ratio above unity, which was in agreement with the predicted values.

Theory of the response of schottky-barrier diodes to transverse magnetic surface waves

Abstract Both the reflectivity and quantum efficiency response functions of a Schottky-barrier diode are calculated for the case when the device is exposed to transverse magnetic surface electromagnetic waves. The surface plasma resonance is shown to occur in both responses Numerical results are presented for a Au/nSi diode.

Recombination-induced random walk diffusion of interstitial carbon in silicon

Recombination events at interstitial carbon atoms in silicon cause the carbon to step to adjacent interstitial positions. DLTS inp-type silicon is used to measure the random walk from interstitial carbon to interstitial carbon-oxygen centers. Electron capture at the interstitial carbon defect causes the carbon to step with a frequency of once per 16 capture events. Using 100 keV electron irradiations to produce electron-hole recombination events, we measure: the step frequency, electron capture cross section, and the mean time between electron captures at the interstitial carbon defect. Measurement of athermal diffusion in the dark indicates that the time between recombination events at interstitial carbon is 0.92 × 1011 seconds if the electron density is 1 m−3. Interstitial carbon moves rapidly at low temperature by this random walk in p-type silicon.

Surface-plasma-enhanced quantum efficiency of a Ag-Ti-n-GaAs grating photodiode.

An array of Ag-Ti-n-GaAs grating photodiodes was designed and fabricated, with each diode having an active area with a diameter of 400 microm. Both electrical and optical characterizations were performed. We have made two experimental observations concerning (1) the surface-plasma-enhanced detectivity as a function of wavelength for 30 degrees angle of incidence and (2) the offset in angle between the reflectivity minimum and the current maximum at the surface-plasma resonance.

Theory of a metal‐semiconductor photodiode with grating coupling of the incident light to surface plasma waves

A theoretical model has been developed to design a metal‐semiconductor (Schottky barrier) narrow‐band photodiode with grating coupling of the incident light to surface plasma waves. With optimal choice of grating parameters and the right combination of materials, the quantum efficiency can be increased over the flat surface geometry. The results of this model are in good agreement with the experimental results found in the literature.

Tuning of the Schottky barrier height using bi‐metallic layered structures

Bi‐metallic Schottky contacts of Cr‐Al on p‐type Si using a layered structure have been investigated. In these contacts, the thickness of the inner layer in contact with Si was varied, while that of the outer metal layer was kept constant. Our studies indicate that the barrier height changes with the thickness of the inner metal layer. Furthermore, the morphology of our samples was examined with a transmission electron microscope (TEM) which indicates the presence of inhomogeneous mixing of Cr and Al.