Type of Document Dissertation Author Rinzan, Mohamed Buhary URN etd-10102006-204618 Title THRESHOLD EXTENSION of GALLIUM ARSENIDE/ALUMINUM GALLIUM ARSENIDE TERAHERTZ DETECTORS and SWITCHING in HETEROSTRUCTURES Degree Ph.D. Department Physics and Astronomy Advisory Committee
Advisor Name Title Unil Perera Committee Chair Donald Edwards Committee Member Gennady Cymbaluyk Committee Member Mark Stockman Committee Member Nikolaus Dietz Committee Member Paul Wiita Committee Member Keywords
- Terahertz detectors
- Homojunction
- Heterojunction
- Free carrier absorption
- Reststrahlen band
- Interfacial workfunction
- Internal photoemission
- Infrared detectors
- Emitters
- Barriers
- Dark current
- Photo current
- Resonance cavity architecture
- Responsivity
- Quantum Efficiency
- Detectivity
- BLIP temperature
- Threshold wavelength
- Negative differential resistance
- Tunneling
- Switching
Date of Defense 2006-05-09 Availability unrestricted Abstract In this work, homojunction interfacial workfunction internal photoemission (HIWIP) detectors based on GaAs, and heterojunctioninterfacial workfunction internal photoemission (HEIWIP) detectors based mainly on the Gallium Arsenide/Aluminum Gallium Arsenide material system are presented. Design principles of HIWIP and HEIWIP detectors, such as free carrier absorption, photocarrier generation, photoemission, and responsivity, are discussed in detail. Results
of p-type HIWIPs based on GaAs material are presented. Homojunction detectors based on p-type GaAs were found to limit their operating wavelength range. This is mainly due to band
depletion arising through carrier transitions from the heavy/light hole bands to the split off band. Designing n-type GaAs HIWIP detectors is difficult as it is strenuous to control their workfunction.
Heterojunction detectors based on Gallium Arsenide/Aluminum Gallium Arsenide material system will allow tuning their threshold wavelength by
adjusting the alloy composition of the Aluminum Gallium Arsenide/Gallium Arsenide barrier, while keeping a fixed doping density in the emitter. The
detectors covered in this work operate from 1 to 128 micron (300 to 2.3 THz). Enhancement of detector response using resonance cavity architecture is demonstrated. Threshold wavelength
extension of HEIWIPs by varying the Al composition of the barrier was investigated. The threshold limit of approximately 3.3 THz (92 micron), due to a practical Al fraction limit of approximately 0.005, can be overcome by replacing GaAs emitters in Gallium Arsenide/Aluminum Gallium Arsenide HEIWIPs with Aluminum Gallium Arsenide/Gallium Arsenide emitters. As the initial step, terahertz absorption for 1 micron-thick Be-doped Aluminum Gallium Arsenide epilayers (with different Al fraction and doping density) grown on GaAs substrates was measured. The absorption probability of the epilayers was derived from these absorption measurements. Based on the terahertz absorption results, an Aluminum Gallium Arsenide/Gallium Arsenide HEIWIP detector
was designed and the extension of threshold frequency (f0) to 2.3 THz was successfully demonstrated.
In a different study, switching in Gallium Arsenide/Aluminum Gallium Arsenide
heterostructures from a tunneling dominated low conductance branch to a thermal emission dominated high conductance branch was investigated. This bistability leads to neuron-like voltage pulses observed in some heterostructure devices. The bias field that initiates the switching was determined from an iterative method that uses feedback information, such as carrier drift velocity and electron temperature, from hot carrier transport. The bias voltage needed to switch the device was found to decrease with the increasing device temperature.
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