Preparation, Photoluminescence Performance And Surface Passivation By Aluminum Deposition Of N-type Porous Silicon

Porous silicon has received considerable attention due to its special luminous performance. With deeper research of PS, great progress has been made in the preparation method and performance research, but many vital problems still exist now for its application as luminous apparatus, such as low luminous intensity, short luminous life-span and poor luminous stability.In this study, n-type porous silicon (n-PS) was prepared on monocrystalline silicon wafer by double-cell electrochemical etching method under lighting condition. The effects of light, etching time, HF concentration, current density and dopant concentration of monocrystalline silicon on formation of n-PS, structure, morphology and photoluminescence (PL) performance were studied by scanning electron microscopy (SEM) and PL spectroscopy with wavelength range of 500～700nm. The results showed that the formation, structure, morphology and PL performance of n-PS were controllable, and n-PS with homogenous pore-size distribution and better PL performance under lighting conditions was obtained. A strong PL peak at about 600nm was observed. With increase of etching time, HF concentration and current density, the PL peak showed red shift at first and then blue shift, and the emission intensity increased at first and then decreased. The maximum value of emission intensity was obtained when the corrosion time, HF concentration and current density was 20min,6% and 60mA/cm2, respectively. The PL performance decreased with increase of the monocrystalline silicon dopant concentration.n-PS was also obtained by pulse electrochemical anodization on a phosphorus-doped n-type silicon wafer, which was different from conventional electrochemical anodization method. The effects of equivalent etching time, pulse frequency and pulse duty cycle on PL performance of porous silicon in the visible light range under room temperature were investigated systematically. The results showed that porous silicon obtained by pulse electrochemical etching had higher PL intensity and showed blue shift of luminescent wavelength under the same conditions compared with constant current density anodization. Moreover, the n-PS obtained by pulse electrochemical etching showed a more uniform surface under scanning electron microscope observation, which also proved that pulse electrochemical anodization was a more excellent etching method.In order to improve the PL performance and stability of n-PS, the electrochemical deposition technique was applied to prepare n-PS samples on the surface. The influence of Al-deposited on the photoluminescence of n-PS was studied by PL spectroscopy, Fourier transform infrared spectroscopy and SEM. The results indicated that Al3+ was deposited on PS surface forming stable Al-Si bonds, which could inhibit the formation of dangling Si bonds effectively. Furthermore, the decreased of dangling Si bonds, which were testified to be non-luminescence centers, could retard the attenuation of PL intensity, and stabilized its PL performance. But, on the other hand, excessive Al3+ deposition had a oxidizing effect on room-temperature visible PL of n-PS.