We analyze theoretically the optical properties of ideal semiconductor crystallites so small that they show quantum confinement in all three dimensions [quantum dots (QD's)]. In the limit of a QD much smaller than the bulk exciton size, the linear spectrum will be a series of lines, and we consider the phonon broadening of these lines. The lowest interband transition will saturate like a two-level system, without exchange and Coulomb screening. Depending on the broadening, the absorption and the changes in absorption and refractive index resulting from saturation can become very large, and the local-field effects can become so strong as to give optical bistability without external feedback. The small QD limit is more readily achieved with narrow-band-gap semiconductors.

Theory of the linear and nonlinear optical properties of semiconductor microcrystallites

The invention provides a method for producing semiconductor particles in which a semiconductor material of the type for which particles are desired is placed in an electrolytic solution of an anodic cell. The anodic cell is configured with a cathode also positioned in the electrolytic solution. The electrolytic solution of the anodic cell includes an etchant and a surfactant that is characterized by an attractive affinity for the semiconductor material. To produce semiconductor particles from the semiconductor material, an electrical potential is applied between the semiconductor material in the electrolytic solution and the cathode in the electrolytic solution to anodically etch the semiconductor material. During the etch process, particles of the semiconductor material form and are encapsulated by the surfactant. This method for producing semiconductor particles uses an uncomplicated apparatus and procedure that results in inexpensive and high-volume production of particles of a semiconductor material.

Method for producing semiconductor particles

Harmonic incident radiation is obtained from a silicon nanoparticle microcrystal or microcrystal film. The preferred film comprises silicon nanoparticles, dimensioned on the order of one nanometer, reconstituted into a device quality crystalline film. The microcrystal film emits the second harmonic of incident radiation for excitations in the range of about 600-1000 nm. A preferred device according to the invention includes a silicon nanoparticle microcrystal film formed on a substrate, such as silicon or glass. Crystals of the silicon nanoparticles, due to the harmonic response, also demonstrate the capability to serve as piezoelectric material and as an improved biological marker. Since the emission response of the silicon nanoparticle crystals will be influenced by surrounding electric fields, the microcrystals also provide for electrochromatic mapping of electric field distribution in general and in electronic devices.

Silicon nanoparticle microcrystal nonlinear optical devices

A silicon nanoparticle having unique properties and being a source of stimulated emissions that also be suspend in liquids and solids is provided by the invention. It can be formed into crystals, clusters, colloids and films. The nanoparticle is dimensioned on an order of magnitude of 1 and not exceeding about 2 nanometers. The method of producing the silicon nanoparticle of the invention comprises placing a silicon wafer (10) and a platinum cathode (12), in the form of a sheet or a wire, in an etchant bath (14), consisting of HF acid, H2O2 liquid and other chemicals, having a surface (20). The wafer and the cathode are connected to a constant current source (16) driven by a power source (18). The silicon wafer (10) is gradually immersed into the bath. A magnetic stirrer (22) ensures that the chemicals of the etchant bath stay uniformly mixed.

Silicon nanoparticle and method for producing the same

A method for producing the silicon nanoparticle of the invention is a gradual advancing electrochemical etch of bulk silicon. Separation of nanoparticles from the surface of the silicon may also be conducted. Once separated, various methods may be employed to form nanoparticles into colloids, crystals, films and other desirable forms. The particles may also be coated or doped.

Method for producing silicon nanoparticles

Technology and photoluminescence of GaAs micro- and nanocrystallites

We have fabricated submicron GaAs crystals by pulverization of bulk material. Size selected crystals exhibit modified photoluminescence spectra with blue shifts of up to 10 meV. The observed behavior is explained by the enhancement and the inhibition of spontaneous emission in a three‐dimensional optical microcavity formed by a semiconductor microcrystal.

K. Überbacher

Papers

Technology and photoluminescence of GaAs micro- and nanocrystallites

Microcavity effects in the photoluminescence of GaAs microcrystals