Date of Graduation

5-2014

Document Type

Thesis

Degree Name

Master of Science in Electrical Engineering (MSEE)

Degree Level

Graduate

Department

Electrical Engineering

Advisor/Mentor

Manasreh, Omar O.

Committee Member

Ang, Simon S.

Second Committee Member

Herzog, Joseph B.

Keywords

Absorbance; Nanocrystals; Optoelectronics; Photodetectors; Spectral Response; Synthesis

Abstract

Room temperature operation is considered one of the essential restrictions in the design of electronic devices. Photodetectors are unable to detect light efficiently at room temperature due to high dark currents. Semiconductor nanocrystals possess unique optical and electrical properties which make them ideal for fabricating uncooled photodetectors. In this project, nanocrystals were synthesized and implemented in devices that detect light at room temperature.

Nanocrystalline I-III-VI2 and II-VI semiconductors (CuInS2 and CdSe) were grown by a wet chemical method, and characterized using: optical absorption, photoluminescence, Raman scattering, and x-ray diffraction. The optical absorption and photoluminescence spectra of the nanocrystals were recorded at different growth reaction times, and showed an increase in the size of the nanocrystals with longer reaction times. The structural properties of CuInS2 nanocrystals were investigated using Raman spectroscopy and x-ray diffraction.

Photodetectors were fabricated by depositing CdSe nanocrystals on interdigitated electrodes with spacing of 5 and 50 µm. The current-voltage curves of the devices showed a low dark current (< 1 nA), and photocurrent higher than the dark current by several orders of magnitude. The room temperature detectivity for the device with 5 µm spacing was extracted from the current-voltage curve and found to be on the order of 3.5x1010 cmHz1/2W-1 at 5 V bias voltage. The onset of the spectral response was positioned at 710 nm, which coincide with the photoluminescence of the nanocrystals. Another type of photodetector was fabricated from semi-insulating GaAs using interdigitated gold electrodes with different spacing (5, 10, 20, and 50 μm). Significant enhancement in the spectral response was observed as the electrode spacing was reduced from 50 to 5 µm. The spectral response of smaller spacing devices (5 and 10 µm) showed dependence on the polarization of incident light.

The integration of nanocrystals with interdigital metallization simplified the device structure, and improved on its performance by reducing the dark current. Furthermore, the interaction between incident light and gold electrodes produced a plasmonic effect. This plasmonic effect is responsible for the enhancement seen in the spectral response spectra.

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