ASU Electronic Theses and Dissertations
This collection includes most of the ASU Theses and Dissertations from 2011 to present. ASU Theses and Dissertations are available in downloadable PDF format; however, a small percentage of items are under embargo. Information about the dissertations/theses includes degree information, committee members, an abstract, supporting data or media.
In addition to the electronic theses found in the ASU Digital Repository, ASU Theses and Dissertations can be found in the ASU Library Catalog.
Dissertations and Theses granted by Arizona State University are archived and made available through a joint effort of the ASU Graduate College and the ASU Libraries. For more information or questions about this collection contact or visit the Digital Repository ETD Library Guide or contact the ASU Graduate College at gradformat@asu.edu.
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- All Subjects: Carrier Lifetime
Description
Carrier lifetime is one of the few parameters which can give information about the low defect densities in today's semiconductors. In principle there is no lower limit to the defect density determined by lifetime measurements. No other technique can easily detect defect densities as low as 10-9 - 10-10 cm-3 in a simple, contactless room temperature measurement. However in practice, recombination lifetime τr measurements such as photoconductance decay (PCD) and surface photovoltage (SPV) that are widely used for characterization of bulk wafers face serious limitations when applied to thin epitaxial layers, where the layer thickness is smaller than the minority carrier diffusion length Ln. Other methods such as microwave photoconductance decay (µ-PCD), photoluminescence (PL), and frequency-dependent SPV, where the generated excess carriers are confined to the epitaxial layer width by using short excitation wavelengths, require complicated configuration and extensive surface passivation processes that make them time-consuming and not suitable for process screening purposes. Generation lifetime τg, typically measured with pulsed MOS capacitors (MOS-C) as test structures, has been shown to be an eminently suitable technique for characterization of thin epitaxial layers. It is for these reasons that the IC community, largely concerned with unipolar MOS devices, uses lifetime measurements as a "process cleanliness monitor." However when dealing with ultraclean epitaxial wafers, the classic MOS-C technique measures an effective generation lifetime τg eff which is dominated by the surface generation and hence cannot be used for screening impurity densities. I have developed a modified pulsed MOS technique for measuring generation lifetime in ultraclean thin p/p+ epitaxial layers which can be used to detect metallic impurities with densities as low as 10-10 cm-3. The widely used classic version has been shown to be unable to effectively detect such low impurity densities due to the domination of surface generation; whereas, the modified version can be used suitably as a metallic impurity density monitoring tool for such cases.
ContributorsElhami Khorasani, Arash (Author) / Alford, Terry (Thesis advisor) / Goryll, Michael (Committee member) / Bertoni, Mariana (Committee member) / Arizona State University (Publisher)
Created2013
Description
Sb-based type-II superlattices (T2SLs) are potential alternative to HgCdTe for infrared detection due to their low manufacturing cost, good uniformity, high structural stability, and suppressed Auger recombination. The emerging InAs/InAsSb T2SLs have minority carrier lifetimes 1-2 orders of magnitude longer than those of the well-studied InAs/InGaSb T2SLs, and therefore have the potential to achieve photodetectors with higher performance. This work develops a novel method to measure the minority carrier lifetimes in infrared materials, and reports a comprehensive characterization of minority carrier lifetime and transport in InAs/InAsSb T2SLs at temperatures below 77 K.
A real-time baseline correction (RBC) method for minority carrier lifetime measurement is developed by upgrading a conventional boxcar-based time-resolved photoluminescence (TRPL) experimental system that suffers from low signal-to-noise ratio due to strong low frequency noise. The key is to modify the impulse response of the conventional TRPL system, and therefore the system becomes less sensitive to the dominant noise. Using this RBC method, the signal-to-noise ratio is improved by 2 orders of magnitude.
A record long minority carrier lifetime of 12.8 μs is observed in a high-quality mid-wavelength infrared InAs/InAsSb T2SLs at 15 K. It is further discovered that this long lifetime is partially due to strong carrier localization, which is revealed by temperature-dependent photoluminescence (PL) and TRPL measurements for InAs/InAsSb T2SLs with different period thicknesses. Moreover, the PL and TRPL results suggest that the atomic layer thickness variation is the main origin of carrier localization, which is further confirmed by a calculation using transfer matrix method.
To study the impact of the carrier localization on the device performance of InAs/InAsSb photodetectors, minority hole diffusion lengths are determined by the simulation of external quantum efficiency (EQE). A comparative study shows that carrier localization has negligible effect on the minority hole diffusion length in InAs/InAsSb T2SLs, and the long minority carrier lifetimes enhanced by carrier localization is not beneficial for photodetector operation.
A real-time baseline correction (RBC) method for minority carrier lifetime measurement is developed by upgrading a conventional boxcar-based time-resolved photoluminescence (TRPL) experimental system that suffers from low signal-to-noise ratio due to strong low frequency noise. The key is to modify the impulse response of the conventional TRPL system, and therefore the system becomes less sensitive to the dominant noise. Using this RBC method, the signal-to-noise ratio is improved by 2 orders of magnitude.
A record long minority carrier lifetime of 12.8 μs is observed in a high-quality mid-wavelength infrared InAs/InAsSb T2SLs at 15 K. It is further discovered that this long lifetime is partially due to strong carrier localization, which is revealed by temperature-dependent photoluminescence (PL) and TRPL measurements for InAs/InAsSb T2SLs with different period thicknesses. Moreover, the PL and TRPL results suggest that the atomic layer thickness variation is the main origin of carrier localization, which is further confirmed by a calculation using transfer matrix method.
To study the impact of the carrier localization on the device performance of InAs/InAsSb photodetectors, minority hole diffusion lengths are determined by the simulation of external quantum efficiency (EQE). A comparative study shows that carrier localization has negligible effect on the minority hole diffusion length in InAs/InAsSb T2SLs, and the long minority carrier lifetimes enhanced by carrier localization is not beneficial for photodetector operation.
ContributorsLin, Zhiyuan (Author) / Zhang, Yong-Hang (Thesis advisor) / Vasileska, Dragica (Committee member) / Johnson, Shane (Committee member) / Goryll, Michael (Committee member) / Arizona State University (Publisher)
Created2016