Akademik Veri Yönetim Sistemi
Tezin Türü: Doktora
Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Fen Bilimleri Enstitüsü, Türkiye
Tezin Onay Tarihi: 2023
Tezin Dili: İngilizce
Öğrenci: EYÜP CAN BALOĞLU
Danışman: Hüsnü Dal
Özet:
Development of Infrared Focal Plane Array (IRFPA) structures have become increasingly important in recent years due to their applications in a wide range of fields,
including thermal imaging, remote sensing, security, surveillance, earh observation
and astronomy. Semiconductor compounds used in IRFPA technologies are typically exposed to a wide range of temperatures during their operation and storage.
Temperature-dependent material properties, such as thermal expansion coefficient,
elastic constants, and heat capacity, play a crucial role in the performance and reliability of IRFPA devices. Therefore, it is important to have accurate and reliable
temperature-dependent material properties for these materials. Having complete and
accurate information about material properties is required for designing and optimizing IRFPA devices. In this thesis, Density Functional Theory (DFT) is implemented
within quasi-harmonic approach to define temperature dependent material properties
which is the first attempt for the selected III-V and II-VI semiconductor compounds
(GaSb, InSb, CdTe, HgTe, ZnTe, CdZnTe). Both LDA and PBEsol approximations
are used to obtain thermo-elastic material properties. Nanoindentation experiments
on GaSb are conducted at room temperature to verify obtained material properties such as elastic modulus and Vicker’s hardness by DFT. Experimental results show
good coherence with numerical outcomes of DFT for GaSb material. To mimic operation conditions of IRFPA structures at cryogenic temperatures, a custom test setup
with cryocooler is designed. Crack initiation and propagation of GaSb and CdZnTe
materials on SS304 material due to developed thermo-mechanical stress by cryocooling are investigated with this test setup and scanning electron microscopy (SEM) is
used to observe cracks at room temperature. Thermo-mechanic stress determinations
on bimaterial assemblies as well as on a representative IRFPA structure are performed
with finite element simulations to show determined stress dependence on defined material properties. A novel phase field fracture model is developed to simulate crack
initiation and propagation for materials that belongs to cubic anisotropy. Anisotropic
energy based failure criterion that splits the free energy and eventually crack driving
source into isotropic and anisotropic parts is used. Representative numerical example
with a notched geometry is also provided for different in plane material orientations
of GaSb. Obtained material properties of GaSb by DFT are used as material inputs
of phase field fracture simulations. Both numerical and experimental investigations
on semiconductor materials are performed. A novel and complete framework on failure analysis of IR sensing materials that cover from temperature dependent material
property determinations to crack initiation/propagation subjects is developed.