Thesis (Ph. D.)--University of Texas at Austin, 2005. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

Not available

The quaternary material system In[subscript x]Ga[subscript 1-x]As[subscript y]P[subscript 1-y] is an important material system for optoelectronic devices, specifically covering optimum fiber optic wavelengths. Among the limitations of using this material system concerning photodetector performance is generation of carriers due to material defects and impurities. This dissertation reports on the growth optimization of InGaAs using molecular-beam epitaxy for low-dark-current avalanche photodiodes through the study of the effects of the growth conditions on dark current. An optimum growth temperature of 545°C and arsenic beam equivalent pressure of 2x10⁻⁵ Torr was found for producing the lowest dark current density. Avalanche photodiodes were implemented with a dark current density 80 mA/cm² at 90% of the breakdown voltage.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (p. 170-178).

Avalanche photodiodes are the primary choice for photodetection in optical access networks, due to their capacity to meet the current requirements of bandwidth and sensitivity introduced by NG-PON2. This work provides an effective tool for modeling and predicting the operation of an avalanche photodiode, paving the way to making better performing receivers. We employed Lumerical to obtain several steady state and transient parameters for a silicon germanium SACM waveguide avalanche photodiode, where close agreement is illustrated between our findings and measurements reported on fabricated devices. The utility of our work is further demonstrated by implementing and modeling a device, designed to meet certain fabrication specifications, where optimization guidelines are suggested afterwards. By providing an accurate approximation of the avalanche photodiode operation, we offer a cost-effective approach to address the problem of fabricating better devices in optical access networks. The introduced methods can be similarly used for other types of photodiodes, contributing to a vast range of applications. / Graduate

No description available.

A self-consistent, full-band, electrothermal ensemble Monte Carlo device simulation tool has been developed. It is used to study charge transport in bulk GaN, and to design, analyze, and improve the performance of AlGaN/GaN high electron mobility transistors (HEMTs) and avalanche photodiodes (APDs). Studies of electron transport in bulk GaN show that both peak electron velocity and saturated electron velocity are higher for transport in the basal plane than along the c-axis. Study of the transient electron velocity also shows a clear transit-time advantage for electron devices exploiting charge transport perpendicular to the c-axis. The Monte Carlo simulator also enables unique studies of transport under the influence of high free carrier densities but with low doping density, which is the mode of transport in AlGaN/GaN HEMTs. Studies of isothermal charge transport in AlGaN/GaN HEMTs operating at high gate bias show a drain current droop with increasing drain-source bias. The cause of the droop is investigated and a design utilizing source- or gate-connected field plate is demonstrated to eliminate the drain current droop. Electrothermal aspects of charge transport in AlGaN/GaN HEMTs are also investigated, and the influence of non-equilibrium acoustic and optical phonons is quantified. The calculated spatial distribution of non-equilibrium phonon population reveals a hot spot in the channel that is localized at low drain-source bias, but expands towards the drain at higher bias, significantly degrading channel mobility. Next, Geiger mode operation of wurtzite GaN-based homojunction APDs is investigated. The influences of dopant profile, active region thickness, and optical absorption profile on single photon detection efficiency (SPDE) are quantified. Simulations of linear mode gain as a function of multiplication region thickness and doping profile reveal that weakly n-type active regions may be exploited to achieve higher avalanche gain, without penalty to either applied bias or active region thickness. A separate absorption and multiplication APD (SAM-APD) utilizing a AlGaN/GaN heterojunction is also investigated. The presence of strong piezo-electric and spontaneous polarization charges at the heterojunction enables favorable electric field profile in the device to reduce dark current, improve excess noise factor, improve quantum efficiency, and improve breakdown probability. To maximize SPDE, a new device structure with a buried absorber is proposed and improved SPDE is demonstrated. Lastly, a new approach for the direct generation of self-sustaining millimeter-wave oscillations is proposed. In contrast to Gunn diodes, which exploit a bulk-like active region, periodic oscillation is achieved in the proposed structures through the creation, propagation and collection of traveling dipole domains supported by fixed polarization charge and the associated two-dimensional electron gas along the plane of a polar heterojunction. Numerical simulation of induced oscillations in a simple triode structure commonly used for AlGaN/GaN HEMTs reveals two distinct modes of self-sustaining millimeter-wave oscillation.