Fast optoelectronic devices

As mentioned above, in oxidized PS and nc-Si a green-blue PL is frequently found [19, 30-32], Because of its fast decay of a few ns or even less, this PL is of great interest with respect to possible applications in fast optoelectronic devices, e.g, for the chip-to-chip communication in computers. The green-blue PL from oxidized PS, nc-Si and from spark-eroded silicon has been attributed to a blue shift in small Si crystallites and clusters which are formed by the oxidation. 

In molecular beam epitaxy (MBE) [317], molecular beams are used to deposit epitaxial layers onto the surface of a heated crystalline substrate (typically at 500-600° C). Epitaxial means that the crystal structure of the grown layer matches the crystal structure of the substrate. This is possible only if the two materials are the same (homoepitaxy) or if the crystalline structure of the two materials is very similar (heteroepitaxy). In MBE, a high purity of the substrates and the ion beams must be ensured. Effusion cells are used as beam sources and fast shutters allow one to quickly disrupt the deposition process and create layers with very sharply defined interfaces. Molecular beam epitaxy is of high technical importance in the production of III-V semiconductor compounds for sophisticated electronic and optoelectronic devices. Overviews are Refs. [318,319],... 

I refer to the original papers for further results [29, 42]. It is an open question wether this fast luminescence can be used for optoelectronic devices. The strong sensitivity of the PL to environmental humidity and temperature may be a limiting factor. Nevertheless, it is an interesting challenge to determine the microscopic mechanism that is common to this PL phenomena, which occurs in so many different systems. 

The recent results clearly show that the green-blue PL from heavily oxidized nc-Si and PS is due to silanol groups. This rises the question if this very fast PL can be used in optoelectronic devices. 

Second-order nonlinear optics (NLO) has several applications in the field of optoelectronics.11 Several of these nonlinear processes are straightforward to experimentally demonstrate but their application in devices has been hampered by the lack of appropriate materials. Necessary requirements for second-order nonlinear optical materials include the absence of centrosymmetry, stability (thermal and mechanical), low optical loss, and large and fast nonlinearities.8... 

Quantum effects, such as resonant tunneling, enhanced carrier mobility (two-dimensional electron gas), bound states in the optical absorption spectrum, and nonlinear optical effects (e.g., intensity-dependent refractive indices) have been observed in semiconductor multiple quantum wells (2-4), Examples of devices based on these structures include tunnel diodes, fast optical and optoelectronic switches, high electron mobility transistors, and quantum well lasers. 

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