Simulation of Electrothermal Characteristics of SSI-LEDs
Authors: Shukla Abhinav , Kuo Yue 
Published: May 2020

A novel type of solid-state incandescent light emitting device (SSI-LED) that emitted broad-band warm white light was reported by Kuo’s group [1-4]. The light emission characteristics is similar to the sunlight in visible wavelength range [1]. The device is made from a simple metal-oxide-semiconductor (MOS) capacitor with a high-k gate dielectric deposited on a p-type Si substrate [1-4]. Hard dielectric breakdown of the amorphous high-k thin film in the device results in the formation of nano-sized conductive paths which emit light upon the passage of a current. The light emission principle is the thermal excitation of the nano-resistor similar to the black body radiation process [4]. In this paper, authors correlate the blackbody emission spectrum with the experimentally measured emission spectrum and estimate certain device characteristics.

Equation 1 is the equation of the spectral radiance B(λ,T), which is the power emitted per unit area of the body, per unit solid angle of emission in the wavelength interval λ to λ + Δλ (Δλ denotes an increment of wavelength) at absolute temperature T, from the black-body radiation theory according to the Planck’s law [5,6], where h is Planck’s constant, c is the speed of light and k is the Boltzmann constant.

Figure 1(a) is the comparison of spectra calculated from equation 1 at 3,000K and 4,000K, separately, and the experimentally measured optical emission spectrum from a 300 µm diameter SSI-LED. The SSI-LED was made from a MOS capacitor with a 8.9 nm thick ZrHfO gate dielectric driven at a gate voltage of -20 V. The detailed fabrication process of this SSI-LED was reported in ref. 2. The effective temperature of sunlight, defined by the total radiative power per square unit, is about 5,780 K which is used as a reference to make initial guess for temperatures used in equation 1 [7]. This figure shows that the light emitted from the SSI-LED is similar to that emitted from nano-resistors heated at 4,000K.

Figure 1(b) shows the comparison of spectra of 1) the black body emission at 4,000K filtered with an annealed ITO film and 2) measured from an SSI-LED made from ref. 2 process. The optical transmittance data of a 500 nm thick ITO film was taken from ref. 8. Although the ITO layer thickness in the SSI-LED was only 80 nm, the result on the ITO filtration effect does not change as the thickness only changes the light intensity not the spectral distribution.

In this study, it was assumed that all nano-resistors in the SSI-LED were of the same size of about 100 nm in diameter. Actually, nano-resistors were formed in different sizes [4]. Under the same gate voltage driven condition, the temperature of the nano-resistor varies with the size. In this presentation, the nano-resistor size effect on the emission spectrum will be presented. In addition, the distribution of nano-resistors across the whole device, which is dependent on the size of the gate electrode, will be discussed.

[1] Y. Kuo and C.-C. Lin, Appl. Phys. Lett.,
102, 031117 (2013).

[2] Y. Kuo and C.-C. Lin, Electrochem. Solid-State Lett.
,
2, Q59 (2013).

[3] Y. Kuo and C.-C. Lin, Solid-State Electron., 89, 120 (2013).

[4] C.-C. Lin and Y. Kuo, Appl. Phys. Lett., 106, 121107 (2015).

[5] M. Planck, The Theory of Heat Radiation, M. Masius, (transl.) (2nd ed.) (1914).

[6] J. Agassi, Science, 156, 3771 (1967).

[7] NASA Sun Fact Sheet. (updated 2018, Feb 23). Retrieved Oct 26, 2019, from https://nssdc.gsfc.nasa.gov/planetary/factsheet/sunfact.html.

[8] J. Zhang, A. C. E. Chia and R. R. LaPierre, Semicond. Sci. Technol.,
29, 054002 (2014).

Figure 1