Date of Award

2015-01-01

Degree Name

Doctor of Philosophy

Department

Electrical Engineering

Advisor(s)

Stella Quinones

Abstract

The material, fabrication and operation parameters for mercury cadmium telluride (HgCdTe) detectors require high sensitivity, small pixel size, low defect density, long-term thermal-cycling reliability and large area substrates. The focus of this work is on the epitaxial growth of CdTe thin films on Si(111) and Si(211) for the purpose of using the resulting material as a substrate for the subsequent growth of HgCdTe thin films. Currently, there is an interest to improve the quality of epitaxial thin films associated with the fabrication of HgCdTe infrared and X-ray imaging using the close-spaced sublimation (CSS) technique. The CSS technique is proven to produce high-quality CdTe films and is associated with high growth rates (> 1 μm/h) compared to molecular beam epitaxy (MBE) and metalorganic vapor phase epitaxy (MOVPE) [1-3]. The higher cost and size limitation of high quality bulk CdTe substrates make Si substrates a more practical alternative. The use of Si substrates also allows the readout circuitry to be implemented on one chip.

There is a 19% lattice mismatch between CdTe and Si, which results in defects at the interface. The nanoheteroepitaxy (NHE) technique makes it possible to grow CdTe on Si substrates, usually with a ZnTe buffer layer, in order to decrease the defect density at the CdTe/Si interface [4]. It is expected that defects will be minimized for selective growth at the nanoscale as a result of strain partitioning between the substrate and the epilayer, which leads to a reduction in the number of defects at the interface [3,4].

Epitaxial CdTe growth on Si(211) substrates produces the highest quality material [5-9]. In contrast, polycrystalline CdTe grown for solar cell applications, results in CdTe grown predominately in the (111) orientation [10-13]. This study is based on observations from the literature associated with the fabrication parameters that affect the quality of CdTe growth. These include the substrate temperature, source temperature, reactor pressure, substrate orientation, source quality and pattern/pillar size [3,5,6,8,9]. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) is used

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to determine the effect of these fabrication parameters on the quality of the CdTe growth and the misorientation at the CdTe/Si interface.

Language

en

Provenance

Received from ProQuest

File Size

109 pages

File Format

application/pdf

Rights Holder

Aryzbe Najera

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Engineering Commons

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