Voltage-Controlled Anodic Oxidation of Porous Fluorescent SiC for Effective Surface Passivation

Abstract

This study investigated the fabrication of porous fluorescent SiC using a constant voltage-controlled anodic oxidation process. The application of a high, constant voltage resulted in a spatial distinction between the porous structures formed inside the fluorescent SiC substrates, due to the different etching rates at the terrace and the large step bunches. Large, dendritic porous structures were formed as the etching process continued and the porous layer thickened. Under the conditions of low hydrofluoric acid (HF) concentration, the uniformity of the dendritic porous structures through the entire porous layer was considerably improved compared with the conditions of high HF concentration. The resulting large uniform structure offered a sizable surface area, and promoted the penetration of atomic layer-deposited (ALD) Al2O3 films (ALD–Al2O3). The emission intensity in the porous fluorescent SiC was confirmed via photoluminescence (PL) measurements to be significantly improved by a factor of 128 after ALD passivation. With surface passivation, there was a clear blueshift in the emission wavelength, owing to the effective suppression of the non-radiative recombination rate in the porous structures. Furthermore, the spatial uniformity of emitted light was examined via PL mapping using three different excitation lasers, which resulted in the observation of uniform and distinctive emissions in the fluorescent SiC bulk and porous areas.

Improved passivation depth of porous fluorescent 6H-SiC with Si/C faces using atomic layer deposition

“…The surface morphologies of fluorescent SiC grown on Si and C faces are quite different in terms of step bunching. In Si-face samples a and b, large white curved belts and gray regions can be found at the surface, which correspond to giant step bunching and terraces, 28) respectively, as confirmed in the AFM image shown in Figs. 2(b) and 2(c).…”

“…A Teflon cell with an 8 mm-diameter-hole at the bottom was aligned with the acid-resistant sheet and fixed by screws from the backside of the stainless-steel plate. 28) The Teflon container was attached with a platinum (Pt) wire. The stainless-steel plate and the Pt wire were used as the anode and cathode, respectively.…”

“…18,23,25) The intensity of porous fluorescent SiC is low after etching, but it can be dramatically improved using atomic layer-deposited (ALD) dielectric films. [26][27][28] By combining the fluorescent SiC and porous fluorescent SiC, a spectrum that covers a wide range of visible light can be obtained, and high color rendering can be realized. For general light sources, the emission efficiency still needs to be significantly improved because of the limitation of ALD passivation depth in the porous layer.…”

“…An impressive enhancement (128 times) in the emission intensity was demonstrated in our published work by applying the constant-voltage-controlled anodic-oxidation method. 28) Nevertheless, large steps and terraces comprising uniform micro-step bunches were observed in the epitaxial fluorescent SiC layer on Si-face substrate, leading to the nonuniform distribution of porous structures after anodic etching. 27) It is known that the anodic etching for Cterminated surfaces is quite different from that on Siterminated SiC owing to their dissimilar chemical stability.…”

“…According to the optimized etching condition in Ref. 28, the effects of the current waveform (electron injection mode) and the difference in the exposed surface (Si or C) on the porous structure and luminescence properties were investigated. The non-uniform distribution of porous structures observed on the Si-face surface was suppressed in C-face SiC, and the anodic etching rate was promoted using pulsed-voltage supply mode.…”