Laser induced impact ionization in semiconductors: A Monte Carlo study for silicon

Monte Carlo computer simulations are carried out to study impact ionization due to a sinusoidal field present in high‐power laser pulses. As an application we study the impact ionization coefficient, α, for electrons in silicon as a function of the field frequency, pulse width, and the rms value of the field. In all cases we stay below the frequency values where band‐to‐band absorption would create electron‐hole pairs. As is the case for constant (dc) fields, log α is found to be linear with field strength. For fields oscillating at frequencies much below the inverse of the carrier scattering rate, the impact ionization coefficient is found to have the same value as in the constant field case with the rms field replacing the dc value. At higher frequencies the impact ionization rate decreases. The dependence of α on field frequency and pulse width is studied. © 1996 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70365/2/APPLAB-68-14-1936-1.pd

Conduction band offset in InAs/GaAs self-organized quantum dots measured by deep level transient spectroscopy

The heterostructure conduction band offset, ΔEc,ΔEc, in InAs/GaAs self-organized quantum dots has been measured by deep level transient spectroscopy. Measurements were made with Au–Al0.18Ga0.82AsAu–Al0.18Ga0.82As Schottky diodes in which the multilayer dots are embedded in the ternary layer. The estimated value of the band offset ΔEc = 341±30 meV.ΔEc=341±30meV. © 2000 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69734/2/APPLAB-76-18-2571-1.pd

Raster-scan imaging with normal-incidence, midinfrared InAs/GaAs quantum dot infrared photodetectors

We demonstrate normal incidence infrared imaging with quantum dot infrared photodetectors using a raster-scan technique. The device heterostructure, containing multiple layers of InAs/GaAs self-organized quantum dots, were grown by molecular-beam epitaxy. Individual devices have been operated at temperatures as high as 150 K and, at 100 K, are characterized by λpeak = 3.72 μm,λpeak=3.72μm, Jdark = 6×10−10 A/cm2Jdark=6×10−10A/cm2 for a bias of 0.1 V, and D∗ = 2.94×109 cm Hz1/2/WD∗=2.94×109cmHz1/2/W at a bias of 0.2 V. Raster-scan images of heated objects and infrared light sources were obtained with a small (13×13)(13×13) interconnected array of detectors (to increase the photocurrent) at 80 K. © 2002 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70691/2/APPLAB-80-18-3265-1.pd

RAPID COMMUNICATION: Lateral hopping conductivity and large negative magnetoresistance in InAs/AlGaAs self-organized quantum dots

We report experimental studies on lateral transport in self-organized quantum dots. We find that below 100 K, conduction occurs through interdot hopping and that experimental results are described quite well by a variable-range hopping model. In the hopping regime, the in-plane conductance varies as G = G0exp [(-T0/T)1/3], and T0 is found to be 7100-9400 K. We have also observed a large negative magnetoresistance in this structure.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48914/2/d215l1.pd

Electronic phenomena in self -organized quantum dots: Theory and applications.

Self-organized quantum dots provide great promise for many novel electronic and optoelectronic devices. This work focuses on various aspects electron transport in heterostructures, which include self-organized quantum dot layers. Tunneling between pairs of laterally and vertically coupled InAs and In 0.4Ga0.6As quantum dots is investigated from a theoretical perspective. Vertical tunneling can be quite fast, but lateral tunneling, on the other hand, is quite slow due to the rather large tunneling distances involved. The vertical tunneling rate is found to agree quite well with the results measured by differential transmission experiments. Lateral transport through quantum dot layers is also studied, both experimentally and theoretically and both at low fields and at high fields. The dominant mechanism of such lateral transport is via hopping conduction at low temperatures and via thermal activation at high temperatures. In addition to studying the material properties of self-organized quantum dot heterostructures, devices, which take advantage of the properties, were also investigated. The excited carrier lifetime in quantum dot inter-subband detectors is calculated using a Monte Carlo model, which reveals that the lifetime increases as the applied bias is increased. By increasing the bias under which the device is place, the electrons become more energetic and therefore less likely to be captured. Detector parameters such as photoconductive gain are calculated which agree with previous experimental results. Finally, a vertical quantum dot FET is designed and fabricated. The source-drain current of this device shows a large negative differential resistance at room temperature.Ph.D.Applied SciencesElectrical engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/132311/2/3057990.pd

Evidence of interdot electronic tunneling in vertically coupled In0.4Ga0.6AsIn0.4Ga0.6As self-organized quantum dots

Ultrafast differential transmission spectroscopy with a resonant pump reveals evidence of electronic tunneling among the excited levels of vertically aligned In0.4Ga0.6AsIn0.4Ga0.6As self-organized quantum dots. This evidence of tunneling is observed as a rapid spectral redistribution of electrons within a few hundred femtoseconds of optical excitation. Measurements show that this spectral spread is independent of carrier density and, therefore, indicate that carrier–carrier scattering is not the main mechanism for carrier redistribution. Instead, electronic tunneling is responsible for the interdot coupling; tunneling rate calculations agree reasonably with the experiment, supporting this conclusion. © 2000 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70974/2/APPLAB-76-17-2394-1.pd

Submicron three-dimensional infrared GaAs/AlxOyGaAs/AlxOy-based photonic crystal using single-step epitaxial growth

A relatively simple technique is demonstrated to fabricate three-dimensional face-centered-cubic infrared photonic crystals with submicron feature sizes using GaAs-based technology, single-step epitaxial growth, and lateral wet oxidation. The photonic crystals were fabricated with feature sizes (a) of 1.5 and 0.5 μm. Transmission measurements reveal a stopband centered at 1.0 μm with a maximum attenuation of 10 dB for the submicron (a = 0.5 μm)(a=0.5μm) photonic crystal. This technique is scalable to small photonic crystal periodicity and hence to shorter wavelengths. © 2001 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70323/2/APPLAB-78-20-3024-1.pd