Electrical and Computer Engineering ETDs

Author

Jiayi Shao

Publication Date

2-1-2012

Abstract

Quantum Dot Infrared Photodetector (QDIP) Focal Plane Arrays (FPAs) have been proposed as an alternative technology for the 3rd generation FPAs. QDIPs are emerging as a competitive technology for infrared detection and imaging especially in the midwave infrared (MWIR) and longwave infrared (LWIR) regime. These detectors are based on intersubband transitions in self-assembled InAs quantum dots (QDs) and offer several advantages such as normal incidence detection, low dark currents and high operating temperatures, while enjoying all the benefits of a mature GaAs fabrication technology. However, due to Stranski-Krastanov (SK) growth mode and the subsequent capping growth, the conventional SK QDs are pancake shaped' with small height to base ratio due to interface diffusion. Thus they cannot fully exploit the 3D 'artificial atom' properties. This dissertation work investigates two approaches for shape engineered QDs: (1) Selective capping techniques of Stranski-Krastanov QDs, and (2) Growth of Sub-Monolayer (SML) QDs. Using Molecular Beam Epitaxy (MBE) growth, engineered QDs have been demonstrated with improved dot geometry and 3D quantum confinement to more closely resemble the 3D 'artificial atom'. In SK-QDs, the results have demonstrated an increased dot height to base aspect ratio of 0.67 compared with 0.23 for conventional SK-QD using Transmission Electron Microscope (TEM) images, enhanced s-to-p polarized spectral response ratio of 37% compared with 10% for conventional SK-QD, and improved SK-QDIP characterization such as: high operating temperature of 150K under background-limited infrared photodetection (BLIP) condition, photodetectivity of 1x109 cmHz1/2/W at 77K for a peak wavelength of 4.8 μm, and photoconductive gain of 100 (Vb=12V) at 77 K. In SML-QDs, we have demonstrated dots with a small base width of 4~6 nm, height of 8 nm, absence of wetting layer and advantage optical property than the SK-QDs. SML-QD shows adjustable dot height to base aspect ratio of 8nm/6nm, increased s-to-p polarized spectral response ratio of 33%, and a narrower full width at half maximum (FWHM), long wavelength 10.5 μm bound-to-bound intersubband transition, and higher responsivity of 1.2 A/W at -2.2 V at 77K and detectivity of 4x109 cmHz1/2/W at 0.4 V 77K.'

Sponsors

the National Science Foundation (NSF), the Air Force Research Laboratory (AFRL), the Air Force Office of Scientific Research (AFOSR), and Korea Research Institute of Standard and Science (KRISS), and the Intelligence Community (IC) Postdoctoral Program

Document Type

Dissertation

Language

English

Degree Name

Electrical Engineering

Level of Degree

Doctoral

Department Name

Electrical and Computer Engineering

First Advisor

Krishna, Sanjay

First Committee Member (Chair)

Lester, Luke

Second Committee Member

Hayat, Majeed

Third Committee Member

Sheik-Bahae, Mansoor

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