SSI-LEDs made of p-type <100> Si wafers of two different dopant concentrations, i.e., p (~1015 cm-3) and p+ (~1017 cm-3), were fabricated. The Zr-doped HfO2 (ZrHfO) dielectric film was sputtered from a Zr/Hf (12/88 wt. %) target on the substrate in Ar/O2 (1:1) at 5 mTorr and 60 W for 12 min. Then, the sample was annealed at 800°C in N2 for 3 min. Subsequently, an ITO film was deposited on top of the high-k stack and wet-etched into 300 µm-diameter dots as the gate electrodes. An Al film was deposited on the backside of the wafer to form the ohmic contact. Finally, the sample was annealed at 400°C in forming gas for 5 min. The complete SSI-LED was stressed at a gate voltage (Vg) of -25 V for the light emission characteristics.
Figure 1 are top-view photos of light emission from SSI-LEDs made on (a) p and (b) p+ Si wafers. Both photos showed that the light was emitted from many discrete bright dots evenly distributed across the gate electrode. Each dot corresponds to a nano-resistor. The p+ sample contains many more dots than the p sample does. The bright dots were almost distributed everywhere across gate electrode of the p+ substrate device. This is because the breakdown strength decreases markedly with the increase of the substrate doping concentration . Therefore, under the same Vg stress, it is easier to form more conductive paths in the gate dielectric thin film in the p+ sample than in the p sample. The light emission photo of the former looks brighter than that of the latter.
Figure 2 shows the light emission spectra of the p and p+ samples. Both spectra cover the same wavelength range including the visible and some of the near IR lights. The p+ sample has a much higher light intensity than the p sample has, which is consistent with the observation of Fig. 1. The more nano-resistors are formed, the stronger the light is emitted from the SSI-LED. The peak wavelengths of both devices are very close, i.e., 700 nm for the p substrate device and 707 nm for the p+ substrate device. The CIE color coordinates, color correlated temperature (CCT), and color rendering index (CRI) values were calculated and listed in Table 1. Both samples have similar CIE characteristics, which indicates the similar conductive path properties.
In summary, the light emission characteristics of the SSI-LED is influenced by the dopant concentration of the Si wafer, which affects the breakdown of the MOS capacitor and the formation of nano-resistors.
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