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Process Dependence of Defects and Dopants in Wide Band Gap Semiconductor and Oxides

Zhang, Zhichun

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2013, Doctor of Philosophy, Ohio State University, Electrical and Computer Engineering.

Wide band gap semiconductors and oxides have attracted much attention in the last decade because of their various applications to next generation opto- and micro-electronics. My research focuses on the process dependence of the defects and dopants in wide band gap semiconductors and oxides of high-k dielectrics, ZnO and MoS2 .

Ultrahigh speed microelectronics demands high mobility semiconductors such as Ge. We are exploring how to process high-k oxides on Ge to minimize defects that trap charge. For Ge doped HfO2, which has higher k value, combined X-ray absorption spectroscopy (XAS) and depth-resolved cathodoluminescence spectroscopy (DRCLS) measurements identified the defects in Ge doped HfO2. Besides, DRCLS of GeO2/Ge structure demonstrated that different annealing temperature will affect the defects at the GeO2/Ge interface. Understanding the defects evolution under different process condition and controlling the defects density in the high-k dielectric gate stack will promote the development of nanoscale electronic devices.

Wide band gap semiconductor ZnO (Eg = 3.4 eV) is a leading candidate for future opto- and micro-electronics due to its high exciton binding energy, thermochemical stability, environment compatibility, availability of high quality large substrates and potential applications for light-emitting devices and photovoltaics. However, as-grown un-doped ZnO is naturally n-type and controllable p-type doping is still not stable and reliable. The origin of the n-type conductivity is also controversial, so the ability to understand and control the intrinsic and impurity related defects in ZnO is essential. We used nanoscale DRCLS, secondary ion mass spectrometry (SIMS), surface photovoltage spectroscopy (SPS), transient surface photovoltage spectroscopy (TSPS), photoluminescence spectroscopy (PLS) and temperature-dependent Hall-effect (TDHE) measurements to investigate the strong process dependence of Li configuration and electrical property of Li-doped ZnO on thermal treatment, the passivation and doping effect of implanted H in ZnO, the mechanical polishing induced defects and passivation effect of post-polishing diluted HF etching. DRCLS reveals an inverse relationship between the optical emission densities of lithium on zinc sites versus zinc vacancy sites, demonstrating the time dependence of Li interstitials to combine with zinc vacancies in order to form substitutional Li acceptors. The critical annealing time and temperature was determined for lowest defect intensity and highest donor concentration of H implanted ZnO. Post polishing HF etching not only removes/passivates zinc vacancy (VZn) related defects, but also decreases oxygen vacancy (VO) related defects by one order of magnitude. Understanding the process dependence of the H and Li configurations and properties in ZnO will provide guidance to control electrical property of ZnO, produce low resistivity in situ auto doped n-type ZnO bulk as well as realize stable p-type ZnO.

Two-dimensional materials are attractive for next generation nanoelectronic devices. Monolayer MoS2 has emerged as a very promising material due to its distinctive electronic, optical and catalytic properties. As a prospective material to substitute for graphene, properties of MoS2 need to be explored. We used DRCLS, SEM, AFM and SPS to characterize the band gap and defect states in thin layer MoS2. The results provide guidance to fabricate monolayer MoS2 and control the defects in MoS2.

Leonard Brillson (Advisor)
Wu Lu (Committee Member)
Siddharth Rajan (Committee Member)
191 p.

Recommended Citations

Citations

  • Zhang, Z. (2013). Process Dependence of Defects and Dopants in Wide Band Gap Semiconductor and Oxides [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1366107518

    APA Style (7th edition)

  • Zhang, Zhichun. Process Dependence of Defects and Dopants in Wide Band Gap Semiconductor and Oxides. 2013. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1366107518.

    MLA Style (8th edition)

  • Zhang, Zhichun. "Process Dependence of Defects and Dopants in Wide Band Gap Semiconductor and Oxides." Doctoral dissertation, Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1366107518

    Chicago Manual of Style (17th edition)