Youn Gyoung Chang

DC Versus Pulse-Type Negative Bias Stress Effects on the Instability of Amorphous InGaZnO Transistors Under Light Illumination

We report that a pulsed negative bias stress slightly deteriorates the photoelectric stability of amorphous InGaZnO thin-film transistors, whereas a dc negative bias stress induces a large threshold voltage shift under the light. In the case of pulsed bias stresses, many of photoexcited positive charges might be recombined during the interval between pulses while those charges under dc bias drift to the channel interface without recombination. Interfacial trap density measurements explain the effects of such photoexcited positive charges on the interface.

Trap Density of States Measured by Photon Probe on Amorphous-InGaZnO Thin-Film Transistors

Trap density of states (DOS) for two amorphous InGaZnO thin-film transistors are measured by photoexcited charge-collection spectroscopy (PECCS); free charges trapped at a certain energy level are liberated by the corresponding energetic photons and then electrically collected at the source/drain electrodes. During this photoelectric process, the threshold voltage of TFT shifts and its magnitude provides the DOS information of charge traps. According to the PECCS analysis, the TFT with a channel deposited under high sputtering power appeared more stable than the other device prepared with low sputtering power, showing even less than ~1010 cm-2 as its totally integrated trap density.

Photoelectric probing of the interfacial trap density-of-states in ZnO nanowire field-effect transistors

We have fabricated transparent top-gate ZnO nanowire (NW) field effect transistors (FETs) on glass and measured their trap density-of-states (DOS) at the dielectric/ZnO NW interface with monochromatic photon beams during their operation. Our photon-probe method showed clear signatures of charge trap DOS at the interface, located near 2.3, 2.7, and 2.9 eV below the conduction band edge. The DOS information was utilized for the photo-detecting application of our transparent NW-FETs, which demonstrated fast and sensitive photo-detection of visible lights.