Optoelectronic Characteristics of Direct-Current and Alternating-Current White Thin-Film Light-Emitting Diodes Based on Hydrogenated Amorphous Silicon Nitride Film

Direct-current and alternating-current white thin- film light-emitting diodes (DCW and ACW TFLEDs) have been fabricated and demonstrated with the intrinsic hydrogenated amorphous silicon nitride (i-a-SiN:H) film as the luminescent layer. The achievable brightness of the representative DCW and ACW TFLEDs were 200 and 170 cd/m² at an injection-current density of 600 and 100 mA/cm², respectively. The electroluminescence (EL) threshold voltage of the DCW TFLED was 10.9 V, and its peak wavelength and full-width at half-maximum (FWHM) of the EL spectrum were about 455 and 230 nm, respectively. For the ACW TFLED, the EL threshold voltage was 8.4 V, and its peak wavelength and FWHM of the EL spectrum were about 535 and 260 nm, respectively. In addition, their current-conduction mechanism was also investigated. Within the lower applied-voltage region, they showed an ohmic current, while for the higher applied-voltage region, the Frenkel-Poole emission was the main mechanism. It was also found that the H₂ -plasma treatment of luminescent i-a-SiN:H layer of an ACW TFLED played an important role in improving device performances, such as decreased EL threshold voltage, increased brightness, and broadened and blue-shifted EL spectrum. The EL spectra of an ACW TFLED under either DC forward or reverse bias or the sinusoidal AC voltage were qualitatively very similar, with a peak wavelength at about 535 nm and a broad FWHM about 260 nm. Moreover, the EL intensity of an ACW TFLED increased with an AC frequency of up to 180 kHz and, then, decreased rapidly and became very weak as the frequency was up to about 500 kHz.