Optical study of the accumulated charge in the amorphous InGaZnO ₄ thin-film transistor

Thin-film transistors (TFTs) with amorphous InGaZnO ₄ as a channel layer are known to exhibit high field-effect mobility. We studied the characteristic of the accumulated carriers in this TFT by optical spectroscopy and observed Drude absorption and oscillation in the transmittance spectrum of the channel region appearing with an applied gate voltage. The scattering rate of the carriers in the accumulation layers estimated from the optical spectrum is ℏ/τAL = 0: 19 eV, and this small value is the origin of the high mobility of the TFT with amorphous InGaZnO ₄.