A large amount of work world-wide has been directed towards obtaining an understanding of the fundamental characteristics of porous Si. Much progress has been made following the demonstration in 1990 that highly porous material could emit very efficient visible photoluminescence at room temperature. Since that time, all features of the structural, optical and electronic properties of the material have been subjected to in-depth scrutiny. It is the purpose of the present review to survey the work which has been carried out and to detail the level of understanding which has been attained. The key importance of crystalline Si nanostructures in determining the behaviour of porous Si is highlighted. The fabrication of solid-state electroluminescent devices is a prominent goal of many studies and the impressive progress in this area is described.

The structural and luminescence properties of porous silicon

http://nathan.instras.com/documentDB/paper-69.pdf

Porous silicon: a quantum sponge structure for silicon based optoelectronics

Recent developments in rare-earth doped materials for optoelectronics

Porous silicon in drug delivery devices and materials

MICROELECTRONIC device integration has progressed to the point where complete 'systems-on-a-chip' have been realized1–3. Now that optoelectronics is becoming increasingly important for information and communication technologies, there is a need to develop optoelectronic devices that can be integrated with standard microelectronics. Conventional semiconductor technology is largely based on crystalline silicon, which (being an indirect bandgap semiconductor) is an inefficient light-emitting material. This has stimulated significant effort towards developing silicon-based optoelectronic components and, of the several strategies explored so far4,5, the use of porous silicon appears the most promising; porous silicon produces high-efficiency, room-temperature, visible photoluminescence6, and its material and optical properties have been studied in detail7,8. But the extreme reactivity and fragility of porous silicon have hitherto prevented its integration with conventional silicon processing technology. We have recently shown9,10 that the thermal and chemical stability of porous silicon can be greatly enhanced — while retaining desirable light-emitting and charge-transport properties — by partial oxidation. Here we take advantage of these improvements in material properties to demonstrate the successful integration of silicon-based visible light-emitting devices into a standard bipolar microelectronic circuit.

Silicon-based visible light-emitting devices integrated into microelectronic circuits

The authors report an all solid state, VLSI compatible, electroluminescent device based on porous silicon with an external quantum efficiency greater than 0.1% under CW operation. The emission, which is broadband and peaks at 600 nm, is detected above a low threshold current density and voltage of 0.01 Am-2 and 2.3 V, respectively.

Electroluminescent porous silicon device with an external quantum efficiency greater than 0.1% under CW operation

On the origin of blue luminescence arising from atmospheric impregnation of oxidized porous silicon

Calcium phosphate nucleation on porous silicon: factors influencing kinetics in acellular simulated body fluids

We have studied the temporal variation of the visible photoluminescence from rapid thermally oxidized porous silicon prepared from n+ substrates. In contrast to the red (slow band) emission, which is observable immediately after high‐temperature oxidation, the blue (fast band) emission is shown to become prevalent only after samples are stored in ambient air. The intensity of the blue emission increases with progressive aging, the magnitude of the increase being dependent on the temperature at which the material is oxidized. Thermal treatment of aged rapid thermally oxidized material can reduce and even quench the blue photoluminescence. Quenching is reversible in that the photoluminescence re‐appears after further aging at room temperature.

Blue photoluminescence from rapid thermally oxidized porous silicon following storage in ambient air

The suitability of ion‐beam‐analysis techniques in quantifying the composition of mesoporous silicon nanostructures has been critically examined using films of moderate porosity (55%) prepared on n+ substrates. The effects of room‐temperature aging of as‐etched and thermally oxidized porous silicon, the oxidation conditions chosen to render the material luminescent, have been carefully monitored, as have the effects of both ion‐beam irradiation and storage of samples in vacuo. It is shown that the concentrations of the three major impurities oxygen, carbon, and hydrogen can be appreciably altered during analyses, thereby limiting the reliability of the techniques, as conventionally applied to porous silicon. The use of appropriate capping layers, which should alleviate the problem, is recommended.

A. Loni

Papers

Electroluminescent porous silicon device with an external quantum efficiency greater than 0.1% under CW operation

On the origin of blue luminescence arising from atmospheric impregnation of oxidized porous silicon

Calcium phosphate nucleation on porous silicon: factors influencing kinetics in acellular simulated body fluids

Blue photoluminescence from rapid thermally oxidized porous silicon following storage in ambient air

Compositional variations of porous silicon layers prior to and during ion‐beam analyses