Complementary metal–oxide–semiconductor (CMOS) colour image sensors are representative examples of light-detection devices. To achieve extremely high resolutions, the pixel sizes of the CMOS image sensors must be reduced to less than a micron, which in turn significantly limits the number of photons that can be captured by each pixel using silicon (Si)-based technology (i.e., this reduction in pixel size results in a loss of sensitivity). Here, we demonstrate a novel and efficient method of increasing the sensitivity and resolution of the CMOS image sensors by superposing an organic photodiode (OPD) onto a CMOS circuit with Si photodiodes, which consequently doubles the light-input surface area of each pixel. To realise this concept, we developed organic semiconductor materials with absorption properties selective to green light and successfully fabricated highly efficient green-light-sensitive OPDs without colour filters. We found that such a top light-receiving OPD, which is selective to specific green wavelengths, demonstrates great potential when combined with a newly designed Si-based CMOS circuit containing only blue and red colour filters. To demonstrate the effectiveness of this state-of-the-art hybrid colour image sensor, we acquired a real full-colour image using a camera that contained the organic-on-Si hybrid CMOS colour image sensor.
Fe doped GST has shown experimentally the ability to alter its magnetic properties by phase change. In this work, we use screened exchange hybrid functional to study the single neutral substitutional 3d transition metal (TM) in crystalline GeTe and GeSb2Te4. By curing the problem of local density functional (LDA) such as over delocalization of the 3d states, we find that Fe on Ge/Sb site has its majority d states fully occupied while its minority d states are empty, which is different than previous predicted electronic configuration by LDA. From early transition metal Cr to heavier Ni, the majority 3d states are gradually populated until fully occupied and then the minority 3d states begin to be filled. In order to study the magnetic contrast, we use lower symmetry crystalline GeTe and GeSb2Te4 as the amorphous phases, respectively, which has been proposed to model the medium range disordering. We find that only Co substitution in r-GeSb2Te4 and s-GeSb2Te4 shows magnetic contrast. The experimental magnetic contrast for Fe doped GST may be due to additional TM-TM interaction, which is not included in our model. It can also be possible that these lower symmetry crystalline models are not sufficient to characterize the magnetic properties of real 3d TM doped amorphous GST.
We report the breakdown behavior of a patterned Ge2Sb2Te5 multiline structure during the voltage-driven electric stress biasing. Scanning Auger microscope analysis shows that the breakdown process accompanies with a phase separation of Ge2Sb2Te5 into an Sb, Te-rich phase and a Ge-rich phase. The phase separation is explained by the incongruent melting of Ge2Sb2Te5 based on the pseudobinary phase diagram between Sb2Te3 and GeTe. It is claimed that this phase separation behavior by incongruent melting provides one of the plausible mechanisms of the device failure in a phase change memory.
We report rapid crystallization of GeTe–Bi2Te3 mixed layers. The as-deposited (GeTe)1−x(Bi2Te3)x (GBT) layers with x>0.5 are fcc crystalline, while the layers with x<0.5 are amorphous, for cosputter deposition at room temperature. We found that Bi2Te3 significantly enhances the crystallization of the GBT layers. Furthermore, both temperature and minimum time required for crystallization (Tc and tc,min) of GBT layers are smaller than those of (GeTe)1−x(Sb2Te3)x (GST) layers. For example, crystallization of GBT layer with x=0.12 occurs at 155.0°C within 30.9ns, which is around 1∕3 of 95.7ns for Ge2Sb2Te5 with Tc=168.5°C.
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