Long wavelength infrared detectors utilizing multiple quantum wells in III-V compound semiconductors
Dodd, Mark Alan
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https://hdl.handle.net/2142/23069
Description
Title
Long wavelength infrared detectors utilizing multiple quantum wells in III-V compound semiconductors
Author(s)
Dodd, Mark Alan
Issue Date
1994
Doctoral Committee Chair(s)
Stillman, Gregory E.
Department of Study
Electrical Engineering
Discipline
Electrical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Electronics and Electrical
Physics, Electricity and Magnetism
Physics, Radiation
Language
eng
Abstract
Data are presented on various infrared detectors based on multiple GaAs/AlGaAs quantum wells. Due to the great flexibility in the growth, dimensions, and composition of these structures, the electrical and optical characteristics of the photodetector may be significantly altered. This investigation explores both theoretically and experimentally the effect of modifying the well and barrier parameters.
As GaAs/AlGaAs-based materials are prevalent in optical generation devices such as LEDs and lasers, it is natural to explore these materials' use for optical receivers as well. While most LEDs and lasers operate in the visible and near infrared (less than one micrometer), structures can operate to detect radiation with longer wavelengths. The simplest method to achieve longer wavelength absorption is through the use of quantum mechanical wells and their associated bound energy states. The energy level of the bound state may be changed by altering the well width or barrier composition. This allows one to tune the spectral response of the photodetector for a given application.
Three fundamental classes of quantum well infrared detectors (QWIDs) are examined. Each of these n-type, well-doped structures has its merits and drawbacks. The bound-to-bound state energy class is shown to have low dark current but also low responsivity. The bound-to-continuum class results in high dark current, high responsivity detectors. The bound-to-miniband QWIDs have low dark currents and moderate responsivity.
All three classes are explored in greater detail in an effort to increase responsivity. This was accomplished by altering the doping profile of the fundamental structure to include doping of the barrier. The results indicate that a factor of six increase is possible for the bound-to-continuum structure. An increase in operating temperature is an additional benefit of the revised doping profile.
As QWIDs do not typically respond to normally incident radiation, an optical grating must be used to couple the radiation so that it may be absorbed. A variety of one- and two-dimensional gratings are studied, and their impact on performance is reported. The fabrication technique used to form the grating is also examined. A deposited metal grating with a thin gold overcoat was found to yield the most efficient coupling and, therefore, the highest responsivity.
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