Effects due to phase separation in InGaN have been identified as having major effects on the performance of devices, in particular light-emitting diodes (LEDs) and injection lasers. However, the ...complexity of the various materials phenomena that can occur has led to a great deal of recent confusion. Much of this confusion can be eliminated by considering the experimentally measured materials properties in the context of the set of physical phenomena occurring during epitaxial growth, including coupling that exists between the various effects. Spinodal decomposition is expected to produce phase separation due to the miscibility gap in InGaN alloys. However, the actual occurrence of this phenomenon has been disputed due to the complexity of real systems. For example, the region of solid immiscibility for InGaN is strongly dependent on elastic strain. In addition, the strain, itself, affects properties such as the bandgap energy. Complicating the analysis of these phenomena is that the solid composition can be affected by elastic strain due to the well-known thermodynamic phenomenon of “compositional pulling”. An additional factor must be considered if the experimentally observed phenomena are to be understood. Thin, lattice mismatched epitaxial layers are coherent with the substrate (or underlying layer). Thus, the actual growth process for the formation of lattice mismatched layers, namely the Stranski–Krastanov (S–K) formation of islands, must be included in any realistic growth model. By considering all the phenomena together, including the coupling between them, it becomes clear that several separate mechanisms exist for phase separation. The focus of this paper is the analysis of the thin (2–3
nm), coherent InGaN layers used in the quantum well structures used for virtually all LEDs and lasers produced by the S–K mechanism. By considering these coupled phenomena together it is possible to arrive at a coherent interpretation of the various materials properties measured using techniques such as high resolution transmission electron microscopy, X-ray diffraction, and optical techniques as well as the device characteristics.
When a semiconductor host is doped by a foreign element, it is inevitable that a volume change will occur in the doped system. This volume change depends on both the size and charge state difference ...between the dopant and the host element. Unlike the "common expectation" that if the host is deformed to the same size as the dopant, then the formation energy of the dopant would reach a minimum, our first-principles calculations discovered that when an external hydrostatic strain is applied, the change of the impurity formation energy is monotonic: it decreases if the external hydrostatic strain is applied in the same direction as the volume change. This effect also exists when a biaxial strain is applied. A simple strain model is proposed to explain this unusual behavior, and we suggest that strain could be used to significantly improve the doping solubility in semiconductor systems.
•Review of thermodynamic aspects of metastable semiconductor alloys.•Discussion of kinetic hindrance regarding phase separation.•Consideration of several categories, including group IV, III/V, II/VI, ...IV/VI and oxide alloys.•Predictions of usefulness of particular metastable semiconductor alloys.
The desire to access new alloys with desirable properties for semiconductor devices has moved the field of semiconductor epitaxial growth into the region of metastable alloys, i.e., those with a thermodynamic equilibrium state of two separate phases; however, utilizing kinetic hindrance, metastable alloys can be grown having a uniform, single phase, i.e., alloys that are thermodynamically unstable, but which are stable for practical purposes such as device fabrication. This review will concentrate on the growth, properties, and applications of these new materials. The materials to be discussed include the group III/V semiconductors as well as group IV, II/VI, IV/VI, oxide, and other semiconductor alloys.
The thermodynamics of semiconductor alloys will be reviewed, including the simple DLP model, that predicts that alloys of elements having very different sizes will be subject to phase separation, as well as the results of first principles calculations. This is followed by a description of the utilization of kinetic effects during epitaxial growth to allow access to metastable, single-phase alloys. This will lead to discussions of specific metastable semiconductor alloys of current interest, including the effects of the microstructure due to metastability on the materials properties. The prospects of these materials for advanced devices will be discussed with an emphasis on the advantages and disadvantages of the microstructure, particularly the formation of coherent compositional fluctuations, on important materials parameters such as minority carrier lifetime, carrier mobility, minority carrier diffusion coefficients, and thermal conductivity.
The effects of the surfactant Sb on InGaN grown by organometallic vapor phase epitaxy (OMVPE) were studied. Eight samples of InGaN were grown with Sb concentrations ranging from 0% to 2.5%. ...Characterization was done by photoluminescence (PL) and atomic force microscopy (AFM). An abrupt change in PL emission peak energy and surface morphology occurred at a certain critical Sb concentration. Above and below this threshold concentration two distinct regimes of surface morphology and PL emission characteristics were observed. This effect was interpreted as due to a surfactant-induced change of surface phase on the InGaN films.
•InGaN thin films were grown by OMVPE using different concentrations of Sb surfactant.•PL emission peak energy of InGaN shifted abruptly at a critical Sb concentration.•A corresponding change in morphology occurred at the critical Sb concentration.•Addition of Sb changed InGaN bandgap and increased In incorporation from 18% to 31%.•We report evidence of a surfactant-induced change of surface phase on InGaN films.
The STAR Time Projection Chamber (TPC) is used to record the collisions at the Relativistic Heavy Ion Collider. The TPC is the central element in a suite of detectors that surrounds the interaction ...vertex. The TPC provides complete coverage around the beam-line, and provides complete tracking for charged particles within ±1.8 units of pseudo-rapidity of the center-of-mass frame. Charged particles with momenta greater than
100
MeV/c
are recorded. Multiplicities in excess of 3000 tracks per event are routinely reconstructed in the software. The TPC measures
4
m
in diameter by
4.2
m
long, making it the largest TPC in the world.
III/V semiconductor alloys have been extensively studied because of their usefulness for electronic and photonic devices. Nevertheless, the search for new alloys for specific applications continues. ...Often, thermodynamic factors restrict the compositional range accessible by epitaxial growth processes, particularly when the size difference between atoms mixing on a particular sublattice is large. This causes solid phase immiscibility, leading to important effects on the epitaxial growth, the resultant alloy properties, and, consequently, device performance. Stringent thermodynamic limits exist for a number of alloys being considered for advanced LED, laser, and solar cell applications where the atomic sizes are very dissimilar, such as GaInN, GaAsN and GaAsBi. This paper will review the basic thermodynamics of the epitaxial growth processes and mixing in semiconductor alloys, as well as the causes and consequences of the resultant complex microstructures.
We report first principles calculations demonstrating a dual-surfactant effect of Sb and H on enhanced Zn, Mg, Be and Cd incorporation in organometallic vapor phase epitaxially grown GaP films. The ...combined effects of Sb and H lower significantly the film doping energy during the epitaxial growth of all the p-type dopants studied, while neither Sb nor H can work alone as effectively. The role of H is to satisfy the electron counting rule. The role of Sb is to serve as an electron reservoir to help electron redistribution. We also predict that due to the low electronegativity of Mg, Sb and H will enhance Mg doping the least among these dopants because Mg as an electron reservoir itself may negate the electron reservoir effect of Sb. Our findings provide an important general physical understanding for p-type doping in III—V thin films.
Thick PZT films have been produced using a combination of spin coating of a composite slurry and subsequent infiltration of PZT producing sol. The effect of adding a Cu
2O–PbO sintering aid and ...repeated sol infiltrations have been studied with the aim of producing dense PZT films. Relative permittivity has been shown to increase with the addition of sintering aid and increased levels of sol infiltration. Measurements of piezoelectric properties indicate that sol infiltrations have no effect on d
33 once a critical density has been exceeded. A sample with approximately 10% closed porosity was obtained following the incorporation of sintering aid and four infiltration steps per layer. This resulted in a mean relative permittivity of approximately 700 and a d
33 of 62 pC/N (poling conditions: 8 V/μm for 5 min at 200 °C).
Anisotropic lateral growth during GaAs (
0
0
1
) epitaxy can have dramatic effects on the evolution of patterned features and surface morphology. Many new opto-electronic devices require growth on ...patterned or non-ideal surfaces. Controlling lateral growth will be essential for the production of these devices. In this study, GaAs epilayers were grown by organometallic vapor-phase epitaxy on patterned GaAs (
0
0
1
) wafers. During these growth experiments, trimethylantimony and trimethylbismuth were used as surfactant precursors to investigate the effects of Sb and Bi on GaAs lateral growth rates. Both surfactants were found to enhance the
1
1
0
lateral growth rate by nearly 300
%, while having a negligible effect on the lateral growth rate in the orthogonal direction. Kinetic simulations assisted in determining a plausible surfactant mechanism: The enhanced
1
1
0
lateral growth rate is due to an increase in the frequency of
1
1
0
diffusion events (decreased hop barrier).
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