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

This paper provides an overview of research developments toward nanometer-scale electronic switching devices for use in building ultra-densely integrated electronic computers. Specifically, two classes of alternatives to the field-effect transistor are considered: (1) quantum-effect and single-electron solid-state devices and (2) molecular electronic devices. A taxonomy of devices in each class is provided, operational principles are described and compared for the various types of devices, and the literature about each is surveyed. This information is presented in nonmathematical terms intended for a general, technically interested readership.

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Overview of nanoelectronic devices

Gold nanoparticles in micellar poly(styrene)-b-poly(ethylene oxide) films—size and interparticle distance control in monoparticulate films

This paper reviews the current developments in the exciting field of self-assembled semiconductor quantum-dot structures during epitaxial growth of lattice mismatched systems. The formation of quantum-sized islands in the coherent Stranski - Krastanow growth mode, with focus on the possibilities of vertical and lateral ordering, and their electronic properties are described in detail. A overview is given of the self-organizing formation and optical properties of buried (InGa)As quantum discs found in a new growth mode in the metalorganic vapour-phase epitaxy of strained layers on high-index semiconductor surfaces.

https://iopscience.iop.org/article/10.1088/0268-1242/11/10/004/pdf

Self-organized growth of quantum-dot structures

Challenges facing the scaling of microelectronics to sub-50 nm dimensions and the demanding material and structural requirements of integrated photonic and microelectromechanical systems suggest that alternative fabrication technologies are needed to produce nano-scale devices. Inspired by complex, functional, self-assembled structures and systems found in Nature we suggest that self-assembly can be employed as an effective tool for nanofabrication. We define a self-assembling system as one in which the elements of the system interact in pre-defined ways to spontaneously generate a higher order structure. Self-assembly is a parallel fabrication process that, at the molecular level, can generate three-dimensional structures with sub-nanometer precision. Guiding the process of self-assembly by external forces and geometrical constraints can reconfigure a system dynamically on demand. We survey some of the recent applications of self-assembly for nanofabrication of electronic and photonic devices. Five self-assembling systems are discussed: 1) self-assembled molecular monolayers; 2) self-assembly in supramolecular chemistry; 3) self-assembly of nanocrystals and nanowires; 4) self-assembly of phase-separated block copolymers; 5) colloidal self-assembly. These techniques can generate features ranging in size from a few angstroms to a few microns. We conclude with a discussion of the limitations and challenges facing self-assembly and some potential directions along which the development of self-assembly as a nanofabrication technology may proceed.

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Using self-assembly for the fabrication of nano-scale electronic and photonic devices

We found a new self-organizing growth mode in the metalorganic vapor-phase epitaxy (MOVPE) on high-index GaAs (311)B substrates to form well-ordered arrays of quantum-dots. The spontaneous interaction of strained InGaAs layers with AlGaAs buffer layers results in high-density rows of disk-shaped InGaAs quantum dots buried within AlGaAs microcrystals due to lateral mass transport. The size and distance of the disks are controlled independently in the mesoscopic size range by the In composition and the InGaAs layer thickness, respectively, without affecting the uniformity and the shape. The photoluminescence spectra exhibit narrow linewidth and high efficiency at room temperature. Buried quantum disk structures are formed also on other GaAs (n11)B substrates and on InP (311)B substrates, indicating this growth mode to be universal in the strained layer growth on high-index semiconductor surfaces.

We have demonstrated that a self-organization phenomenon occurs in strained InGaAs system on InP (311) substrates grown by metalorganic vapor phase epitaxy. This suggests that a similar formation process of nanocrystals exists not only on the GaAs (311)B substrate but also on the InP (311)B substrate. However, the ordering and the size homogeneity of the self-organized nanocrystals are slightly worse than those of the InGaAs/AlGaAs system on the GaAs (311)B substrate. The tensilely strained condition of a InGaAs/InP system with growth interruption in a PH3 atmosphere reveals a surface morphology with nanocrystals even on the InP (100) substrate. It was found that strain energy and high growth temperature are important factors for self-organization on III-V compound semiconductors. Preliminary results indicate that the self-organized nanostructures in strained InGaAs/InP systems on InP substrates exhibit room temperature photoluminescent emissions at a wavelength of around 1.3 p.m.

Self-organization phenomenon of strained InGaAs on InP (311) substrates grown by metalorganic vapor phase epitaxy

We present evidence of the new phenomenon of the direct growth of microstructures by metal-organic vapor-phase epitaxy (MOVPE) on high-index GaAs substrates. One- and zero-dimensional self-faceting by step bunching on GaAs (n11)A substrates produces quantum-wire- and dot-like arrays on GaAs(311)A and GaAs (211)A substrates. The lateral periodicity of self-faceting is controlled by the layer thickness and growth temperature and is directly correlated with the red shift of the luminescence of GaAs/AlGaAs heterostructures. On GaAs (n11)B substrates, well-ordered quantum-dot arrays are formed in a new self-organizing growth mode found in the MOVPE of a sequence of AlGaAs and strained InGaAs films. The InGaAs film spontaneously interacts with AlGaAs buffer layers to form ordered arrays of disk-shaped InGaAs quantum dots buried within AlGaAs microcrystals due to lateral mass transport. The size and distance of the disks can be controlled independently by the In composition and the InGaAs layer thickness. Similar structures are also formed on InP (311)B substrates in the GaInAs/AlInAs and GaInAs/InP material systems. Lateral confinement of carriers in the disks is confirmed by the photoluminescence linewidth which, at room temperature, is as narrow as 13 meV due to reduced thermal broadening.

Self-organized microstructure growth

We have measured the optical properties of self-organized strained InGaAs quantum disks in high magnetic fields. The disks are formed during spontaneous reorganization of a sequence of AlGaAs and strained InGaAs epitaxial films grown on GaAs (311)B substrates by metallorganic vapor-phase epitaxy. The magneto-luminescence properties of these InGaAs quantum disks have been studied for various disks sizes with lateral widths from 100 nm down to 20 nm. We have confirmed that when the lateral confinement exists the exciton binding energy increases even when the spatial extent of the effective potential is greater than the exciton in-plane Bohr radius. This enhancement starts being noticeable when the spatial extent of the potential is two, three times larger than the Bohr radius, where the center-of-mass quantization is negligibly small.

Magneto-optical properties of self-organized strained InGaAs quantum disks

Well-ordered quantum-dot arrays are formed in a new self-organizing growth mode found in the metalorganic vapor-phase epitaxy (MOVPE) of lattice mismatched systems on high-index semiconductor surfaces On GaAs (311)B substrates, strained InGaAs films spontaneously interact with AlGaAs buffer layers to form ordered arrays of disk-shaped InGaAs quantum dots buried within AlGaAs microcrystals due to lateral mass transport The size and distance of the disks can be controlled independently in the nanometer range by the In composition and the InGaAs layer thickness, respectively, without change in the homogeneity in size and shape The formation of buried quantum disks occurs not only on other GaAs (n11)B substrates but also in the case of InP (311)B substrates The uniformity and the ordering of the disks are optimum on GaAs (311)B substrates which is directly reflected in the narrow photoluminescence linewidth and high efficiency On the other hand, on GaAs (n11)A substrates one-a d zero-dimensional self-faceting by step bunching produces wire-and dot arrays on GaAs (311)A and GaAs (211)A substrates, respectively

Richard Nötzel

Papers

Self-organized growth of quantum-dot structures

Self-organization phenomenon of strained InGaAs on InP (311) substrates grown by metalorganic vapor phase epitaxy

Self-organized microstructure growth

Magneto-optical properties of self-organized strained InGaAs quantum disks

Self-ordered quantum dots: A new growth mode on high-index semiconductor surfaces