Humidity and Temperature Annealing Effect on Light Emission Characteristics of SSI-LEDs
Authors: Liu Lingguang , Lin Wen-Shan , Kuo Yue , Zhang Xiaoning 
Published: February 2020

The solid-state incandescent light emitting device (SSI-LED) can emit the broadband white light similar to that of the sunlight in the visible wavelength range [1-4]. The light emitting principle is the thermal excitation of nano-resistors formed from the dielectric breakdown of a MOS capacitor [5]. The intensity of the emitted light is proportional to the intensity of the current passing through nano-resistors [6]. The SSI-LED has a long lifetime of more than 20,000 hours [7]. There are many potential applications of this kind of device, such as lighting and on-chip optical interconnect. In this paper, authors investigated the influence of the humidity and temperature exposure on the light emission characteristics of the SSI-LED.

The SSI-LED was made from the dielectric breakdown of a MOS capacitor that contained a Zr-doped HfO2 (ZrHfO) gate dielectric on a p-type Si wafer with an ITO gate electrode. The fabrication process is described in refs. 3 and 5. The top ITO gate electrode has a diameter of 200 µm, 300 µm, or 400 µm. Before and after the exposure of the SSI-LED to the 80% humidity at 80℃ for 1 hour (Association Environmental System BHD-403 7316), the emission spectra were measured at the gate voltage (Vg
) of -30 V using a StellawNet spectra detector with the SpetraWiz Shortcut program.

Figure 1 shows the spectra of a 200 µm sized device before and after the annealing. The spectrum shifted toward the long wavelength direct after the annealing, i.e., the peak moved from 601 nm to 641 nm. The same phenomenon has been observed on the 300 µm and 400 µm diameter devices. If the temperature can be estimated from the following Wien’s equation [8], the temperature was lowered by the annealing step, i.e., 4,521K vs. 4,822K.

T
λpeak
= 2.898 x 10-3 [1]

where T is the temperature in Kelvin and λpeak

is the peak wavelength in m. If the color correlated temperature (CCT) is estimated from the SpetraWiz Shortcut program, the number was also lowered after the annealing, i.e., 4,109K vs. 3,801K. Also, the CIE chart location of the device was moved toward the ward light region, i.e., (CIEx, CIEy) (0.384, 0.370) vs. (0.378,0.380).

Figure 2 shows curves of the full width at the half maximum (FWHM) of the emission spectrum vs. the diameter of the device before and after the humidity and temperature annealing. The FWHM was increased after the humidity and temperature exposure.

It was reported that the diffusion of H2O through the nano-resistor structure can cause the formation of charge transfer complexes [9], which lowers the resistance and changed the emission spectrum. A detailed discussion of the cause will be presented.

Lingguang Liu acknowledge the financial support of National Natural Science Foundation of China (Grant Number: 61771382) and the Shaanxi International Science and Technology Cooperation and Exchange Program (2018KW-034).

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Figure 1