Mechanism of a remarkable enhancement in the light emission from nanocrystalline porous silicon annealed in high-pressure water vapor

Abstract

To clarify the effect of surface passivation on the optical properties of nanocrystalline porous silicon (PS), the photoluminescence (PL) characteristics of PS have been investigated by employing a high-pressure water vapor annealing (HWA). PS samples with various porosities were prepared on (100)-oriented p-type (4Ωcm) single-crystalline silicon wafers by electrochemical anodization. Some samples were then electrochemically oxidized. The HWA treatment was then applied to the prepared PS samples at 0.5–3MPa and 200–300°C for 2–3h. The PL intensities, spectra, and dynamics after HWA were measured in relation to surface analyses by Fourier-transform-infrared (FTIR) spectroscopy. It is shown that the HWA treatment leads to a drastic enhancement in both the PL efficiency and stability. Under the optimum condition, the PS sample exhibits an extremely high external quantum efficiency of 23% at room temperature. According to the FTIR spectra analyses, silicon nanocrystallites in HWA-treated PS are covered with a high-quality SiO2 tissue. The PL decays are found to be longer than those of as-prepared PS, and become closer to a single-exponential behavior near the PL peak wavelength. The observed high efficiency and stability of PL emission from HWA-treated PS is attributed to (i) suppression of nonradiative surface defect density, (ii) uniform passivation by unstrained thin oxides, and (iii) strong localization of excitons in silicon nanocrystals. This low-temperature treatment is very useful for obtaining highly efficient and stable luminescent PS and devices.

Stabilization of nano‐crystalline porous silicon electroluminescence by high pressure water vapor annealing

“…It was shown that the defect density at the Si/SiO 2 interface was very much reduced by HWA, resulting in reduced non-radiative recombination rates [9]. Furthermore, the SiO 2 network surrounding the Si nanocrystals is mostly unstrained and very uniform, resulting in very good stability of PS structure and PL [10]. The exciton localization in Si nanocrystals was also much enhanced [10].…”

“…This high stability can be readily attributed to outstanding passivation of nanocrystalline silicon surfaces by high quality oxide as a result of HWA. The structure and the PL of HWA-treated PS have previously been studied [9,10]. It was shown that the defect density at the Si/SiO 2 interface was very much reduced by HWA, resulting in reduced non-radiative recombination rates [9].…”

“…HWA is also useful to enhance the efficiency and stability of ECO-treated p-type PS [10], as well as that of n + -type PS [11]. In this paper, the results of EL from devices that include HWA-treated n + -type PS layers are presented.…”

“…Very recently, we have succeeded in obtaining very high PL efficiencies with p-type PS using highpressure water vapor annealing (HWA) [9,10] Indeed, stable PL emission exhibiting a record-high external quantum efficiency of 23% has been achieved. HWA is also useful to enhance the efficiency and stability of ECO-treated p-type PS [10], as well as that of n + -type PS [11].…”

Improvement of the Photoluminescence of Porous Si Powder via Oxidation in Organic Solvents

“…Gelloz et al prepared porous Si treated by high-pressure water vapor annealing [16][17][18][19][20] . Even though this method achieved a drastic enhancement in the PL efficiency, specialized and expensive equipment was required.…”