Super-Eg excitation wavelength dependent Zni-VO complex defects related characteristic
emissions of green, yellow, and orange-red from ZnO QDs are completely inhibited by reducing
oxygen vacancies through the hybridization of Zn interstitials in ZnO QDs with antibonding O-
states of graphene oxide (GO) QDs. Only λex independent violet-purple-blue (V-P-B)
emission resulting from transitions among Frenkel pairs (Zni0-VZn) and the defects Zni0-Oi in ZnO-
GO QDs is successfully achieved. White-light emission from PL QD-LEDs is achieved using a mixture of yellow emissive ZnO and blue emissive ZnO-GO QDs with CIE (0.32, 0.34) excited by a UV LEDs chip (λ = 365 nm). Further, ZnO-GO QD-based deep-blue LEDs (λ = 438 nm) with luminance of 1980 cd/m2, a luminous efficacy (LE) of 2.53 cd/A, and external quantum efficiency (EQE) of 2.78% with CIE (0.16, 0.11) are also realized.
Two-dimensional van der Waals (2D vdWs) materials are a class of new materials that can provide important resources for future electronics and materials sciences due to their unique physical properties. Molybdenum disulfide (MoS2) is one of the most promising n-type TMD semiconductors. Several research groups reported on MoS2 nanosheet based transistors that exhibit satisfactory carrier mobility values with high on/off current ratios. On the other hand, a newly discovered 2D vdWs material, called black phosphorous (BP), has generated considerable scientific and technological interest in the research community. 2D BP also has considerable potential for electronic and optoelectronic applications. This is evidenced by recent research on FETs, diodes, and photodetectors involving few-layered BP flakes.
Here, we report on a high performance MoS2 and BP nanosheet based nonvolatile memory transistors with a poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)) ferroelectric top gate insulator. The MoS2 ferroelectric field-effect transistor (FeFET) shows a highest linear electron mobility value of 175 cm2/Vs with a high on/off current ratio more than 107, and a very clear memory window over 15 V. The program and erase dynamics and static retention properties are also well demonstrated. Our BP ferroelectric FETs (FeFETs) also exhibit a clear memory window of 15 V and a highest linear mobility value of 1159 cm2V-1s-1 with a 103 on/off current ratio at room temperature in ambient air. In order to explore advanced memory applications beyond unit memory devices, we implement two kinds of memory inverter circuits: a resistive-load inverter circuit and a CMOS inverter circuit combined with n-type MoS2.
One of a wide-bandgap semiconductor, Zinc oxide (ZnO) has a near ultraviolet bandgap (3.37 eV) and an exciton binding energy of 60 meV at room temperature (RT), and has several favorable properties, such as high electron mobility, high oscillator strength, and good transparency. In the photoluminescence (PL) spectra of ZnO nanoparticles, the near band edge ultraviolet (UV) emission at 378 nm relevant to direct bandgap of ZnO, and blue light emissions centered at 410, 435, and 465 nm corresponding to Zn interstitial (Zni) to valence band maximum (VBM), and to Zn vacancies (VZn) and green light emission at 540 nm corresponding to conduction band maximum (CBM) to oxygen vacancy (Vo). Ultra-small size quasi consolidated ZnO-graphene nanoparticles was synthesized in which graphene outer layer was chemically attached with ZnO inner core. After attaching graphene to ZnO, green emission completely disappeared whereas the intensity of blue emission was greatly increased. Enhanced blue emission could be well described by both fast electron transfer from CBM of ZnO to graphene having similar molecular energy level with Zni and transition to VBM and Vzn. Glass/ITO/PEDOT:PSS/poly-TPD/ZnO-graphene/Cs2CO3/Al were fabricated and showed the blue emission centered at 435 nm with FWHM of about 90 nm.
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