F. Kozlowski

Current-induced light emission from a porous silicon device

Experiments with light-emitting porous silicon (LEPOS) are described. The porous silicon was made from n-type silicon by anodization in an electrolytic cell by HF with an applied electrical current. Visible light emission was achieved by irradiation with ultraviolet light. Visible electroluminescence (EL) was achieved by applying a DC or AC voltage to a solid-state contact on top of the porous layer. Optical spectra from both experiments are shown.<<ETX>>

Light‐emitting porous silicon diode with an increased electroluminescence quantum efficiency

The fabrication technology and the properties of a light‐emitting device including a porous pn junction are presented. We employ the selective formation of different kinds of porous silicon substructures caused by the doping level and the illumination during anodization. The device has a nanoporous light‐emitting n layer between a mesoporous p+‐doped capping layer and the macroporous n substrate. The pn junction formed in this way has strong rectifying characteristics. It shows bright red‐orange light emission under forward bias. Compared to simple metal‐porous silicon devices, the structure has an increased quantum efficiency (factor 10–100).

Spatially resolved Raman measurements at electroluminescent porous n‐silicon

The cross section of electroluminescent (EL) porous silicon layers (LEPOS) made from n‐ and p‐doped silicon has been investigated by means of micro‐Raman and photoluminescence (PL) spectroscopy to find the luminescence active zone in LEPOS. Special care has been taken to avoid the heating of the sample. Additionally an energy dispersive spectroscopy scan over the sample cross section has been performed for n‐LEPOS to detect the distribution of oxygen. Since the n samples display much better EL properties than the p samples, the investigations concentrate on the n samples. For n‐LEPOS, a layered structure has been found with SiOx/Si at the top followed by a PL active layer. There are two types of samples showing different forms of Raman spectra. Type‐I spectra are narrow and shifted by small values as compared with the Raman spectra of bulk silicon. They have a shoulder at about 510 cm−1 only in the PL active layer. Type‐II spectra are broad and shifted by about 7–10 cm−1. All the electroluminescent sample...

Porous silicon electroluminescent devices

Abstract The electroluminescence of porous silicon and its application are reported. The basic structures are described, the main tasks for the work in the next future are discussed.

Surface-micromachined electrostatic microrelay

Abstract Three variants of electrostatically driven microrelays are reported. These switches have a high off resistance like conventional mechanical relays, but are also characterized by a low power consumption (

Blue and green electroluminescence from a porous silicon device

The fabrication and the characteristics of light-emitting porous silicon devices are presented. A nanoporous layer on n-substrate is formed under the influence of UV illumination during anodization. The wafer shows weak photoluminescence with a maximum at 640 nm. The porous layer is contacted by pads consisting of semitransparent gold. When voltage is applied, electroluminescence in the 560- to 480-nm range can be observed. The current-voltage characteristic is strongly rectifying. Light emission occurs under forward bias. A possible model for the shift of the electroluminescence toward higher energies is given.<<ETX>>

A novel method to avoid sticking of surface-micromachined structures

Abstract Surface-micromachined cantilevers and bridges of 500 nm polysilicon on 900 nm thermal oxide as the sacrificial layer have been fabricated. It is well known that the released structures tend to stick to the substrate during the drying period after the oxide etching in HF and the rinse process. In general it is necessary to solidify the liquid between the polysilicon and the substrate. Thus we have replaced the HF by the monomer divinylbenzene in successive exchange steps. The monomer is polymerized under ultraviolet light at room temperature. Finally the polymer is released in an oxygen plasma. To prevent the fabricated structures from sticking to the substrate after an accidental touch during operation, bumps have been built under the polysilicon structures to keep them at a distance from the substrate.

Enhanced Blue-Light Emission from an Indium-Treated Porous Silicon Device

We present the technology and the performance of blue-light-emitting porous silicon devices. The devices are fabricated using porous silicon formation with UV-light applied. Furthermore, indium is electroplated into the pores, causing an increase of the quantum efficiency. The blue electroluminescence exhibits a peak maximum around 480 nm and an external quantum efficiency of 0.5×10-2 %. Rutherford backscattering spectroscopy (RBS) was employed to measure the stoichiometry and the depth profile of indium in the porous layer.

Electroluminescent performance of porous silicon

Abstract We characterized electroluminescent porous silicon samples made from n-substrates by their luminescence behaviour. Electroluminescence (EL) and photoluminescence (PL) spectra are compared. PL spectra have their peak at about 1.8 eV and a full width at half-maximum of 0.3 eV. EL in the same spectral region is observed for both directions of the current. The spectral distribution of the emitted light, however, depends on the direction of the current. For the investigated samples with contact layers of gold or indium tin oxide, we determined a yield of about 1 photon per 10 5 electrons crossing the sample if bulk n-Si is connected to the positive power supply. The efficiency of light emission depends on the sense of the current.

Micromechanical relay with electrostatic actuation

Three variants of electrostatically driven microrelays are reported. The concepts of these microrelays are a cantilever beam, a fixed-fixed beam and a torsion beam with a double contact configuration. Because of the complete fabrication by surface micromachining technology, there is no need for a chip bonding process. This paper reports on the device concept, fabrication and performance of the microrelay.