K.‐H. Li

Thermal treatment studies of the photoluminescence intensity of porous silicon

Thermal annealing studies of the photoluminescence (PL) intensity and Fourier‐transform infrared spectroscopy have been performed concurrently on porous Si. A sharp reduction in the PL intensity is observed for annealing temperatures ≳300 °C and this coincides with desorption of hydrogen from the SiH2 surface species. A brief etch in HF can restore the luminescence of the samples annealed below 400 °C. We conclude that SiH2 is essential to the visible luminescence in porous Si.

Correlation between silicon hydride species and the photoluminescence intensity of porous silicon

The role of silicon hydride species in the photoluminescence intensity behavior of porous Si has been studied. The surfaces of luminescent porous Si samples were converted to a predominate SiH termination using a remote H plasma. The as‐passivated samples were then immersed in various concentrations of hydrofluouric solutions to regulate the recovery of SiH2 termination on the surface. Photoluminescence measurements and transmission Fourier‐transform infrared spectroscopy have shown that predominant silicon monohydride (SiH) termination results in weak photoluminescence. In contrast, it has been observed that the appearance of silicon dihydride (SiH2) coincides with an increase in the photoluminescence intensity.

Demonstration of photoluminescence in nonanodized silicon

The formation of photoluminescent porous Si in an etchant solution made from the HF‐HNO3‐CH3COOH system is reported. The porous Si is characterized on the basis of its photoluminescence (PL) spectra and the degradation of the PL during exposure to laser irradiation. The surface topography as characterized by atomic force microscopy (AFM) reveals features on the order of 400–600 A. The effect of annealing the porous Si in vacuum on the PL intensity is described and correlated to the breakdown of Si—H bonds on the porous Si surface.

Electroluminescence from porous silicon with conducting polymer film contacts

Visible electroluminescence with a peak wavelength of 6300 A is observed from forward‐biased porous Si p‐n diodes with conducting polymer contacts. These devices have brighter electroluminescence than similar devices with thin, gold‐film contacts. Electroluminescence is also observed from conducting polymer/n‐porous Si diodes.

Control of porous Si photoluminescence through dry oxidation

We demonstrate the applicability of thermal oxidation to control the photoluminescence (PL) from quantum‐sized structures in porous silicon. Uniform photoluminescence samples with intense visible light observed under ultraviolet light at room temperature were quickly obtained without a long time hydrofluoric acid (HF) immersion. Applying different oxidation times or temperatures provides a very practical technique to control the luminescence color. By this way, we have observed a shift in the luminescence peak from 7600 to 6200 A and a reduction in the spectral width from ∼1600 to ∼950 A.

Chemically induced shifts in the photoluminescence spectra of porous silicon

The observation of photoluminescence (PL) spectral shifts during anodization of porous Si and after immersion in different chemical solutions is reported. These shifts in the PL spectra are attributed to changes in the surface chemistry achieved by changing the composition of the electrolyte in which the samples are immersed. Using this approach the emission has been repeatedly cycled (≳100 times) between green and red.

Photodetectors fabricated from rapid-thermal-oxidized porous Si

A metal‐semiconductor‐metal (MSM) photoconductor and a p‐n photodiode have been fabricated from rapid‐thermal‐oxidized (RTO) porous Si. The MSM photoconductor achieved 2.8×higher responsivity at 350 nm than a UV‐enhanced Si photodiode, and the RTO photodiode exhibited an external quantum efficiency of 75% at 740 nm.

Investigation of rapid‐thermal‐oxidized porous silicon

We report that the photoluminescence of porous Si that was quenched by low‐temperature thermal annealing was restored by further annealing in an oxygen atmosphere at high temperature (750 °C≤T≤1100 °C). The intensity of the photoluminescence recovered to near the as‐anodized value and the peak wavelength was red shifted by approximately 100 nm. The oxidized porous Si has been found to have lower resistance and higher photoelectric efficiency than as‐anodized material.

Effects of illumination during anodization of porous silicon

The effects of illumination during anodic etching of porous Si have been studied. For a fixed current density and anodization time, it has been observed that below a critical irradiance level, increasing the radiant flux density during anodization results in higher photoluminescence and a blue shift of the photoluminescence spectra. For irradiance above the critical value, the photoluminescence intensity decreases. Transmission Fourier-transform infrared spectroscopy, x-ray photoelectron spectroscopy and atomic force microscopy have been employed to investigate the effects of illumination on the characteristics of porous Si.

Photoluminescence of porous silicon buried underneath epitaxial GaP

Recent observations of visible, room‐temperature photoluminescence in porous Si have stimulated research aimed at the realization of efficient, Si‐based electroluminescent devices. To achieve electroluminescence, it may be beneficial to generate carriers with sufficient energy to populate the states of the quantum‐confined Si structures. A viable method to accomplish this is to utilize a wide‐band‐gap heterojunction injector, such as GaP. Toward that end, we report the successful formation of porous Si buried underneath GaP islands, and we demonstrate that the buried porous Si layer exhibits strong photoluminescence (λ≊7000 A).