Size dependent bandgap of molecular beam epitaxy grown InN quantum dots measured by scanning tunneling spectroscopy
TL;DR: In this paper, a surface bandgap of InN QDs was estimated from scanning tunneling spectroscopy (STS I-V curves and found that it is strongly dependent on the size of QDs.
Abstract: InN quantum dots (QDs) were grown on Si (111) by epitaxial Stranski-Krastanow growth mode using plasma-assisted molecular beam epitaxy. Single-crystalline wurtzite structure of InN QDs was verified by the x-ray diffraction and transmission electron microscopy. Scanning tunneling microscopy has been used to probe the structural aspects of QDs. A surface bandgap of InN QDs was estimated from scanning tunneling spectroscopy (STS) I-V curves and found that it is strongly dependent on the size of QDs. The observed size-dependent STS bandgap energy shifts with diameter and height were theoretical explained based on an effective mass approximation with finite-depth square-well potential model.
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TL;DR: Indium Nitride (InN) quantum dots (QDs) were synthesized on Si substrate by oblique angle deposition method and the deposited InN QDs were of the order of 5-50"nm in diameter with density ∼7"×"109/cm2 as discussed by the authors.
Abstract: Indium Nitride (InN) quantum dots (QDs) were synthesized on Si substrate by oblique angle deposition method. The deposited InN QDs were of the order of 5–50 nm in diameter with density ∼7 × 109/cm2. The synthesized InN QDs were nearly single crystalline, confirmed from the diffraction peak in the direction. Photoluminescence (PL) measurement showed peak emission at ∼1138 nm (1.08 eV) at 19 K. The PL emission energy exhibited blue shift and the intensity reduced with an increase in temperature. The high optical band gap emission of the InN QDs is possibly due to energy level quantization resulted from size reduction. The free carrier concentration was found to be ∼2 × 1018 cm−3. The device selectively detected the 1080 nm (1.13 eV) wavelength with maximum responsivity near the optical band edge at 10 K and room temperature (300 K) respectively. The external quantum efficiency of ∼4.1% was calculated for the detector at 10 K. The device showed excellent temporal response with rise and fall times of 3.181 s and 3.408 s respectively at 10 K.
10 citations
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TL;DR: In this article, the authors studied the temperature dependence of selective delocalization process through scanning tunneling spectroscopy and found that the electrons are confined to the core at low temperatures and above a certain temperature, they become delocalized up to the shell leading to a decrease in the conduction band edge.
Abstract: Core-shell nanocrystals having a type-I band-alignment confine charge carriers to the core. In this work, we choose CdSe/CdS core-shell nano-heterostructures that evidence confinement of holes only. Such a selective confinement occurs in the core-shell nanocrystals due to a low energy-offset of conduction band (CB) edges resulting in delocalization of electrons and thus a decrease in the conduction band-edge. Since the delocalization occurs through a thermal assistance, we study temperature dependence of selective delocalization process through scanning tunneling spectroscopy. From the density of states (DOS), we observe that the electrons are confined to the core at low temperatures. Above a certain temperature, they become delocalized up to the shell leading to a decrease in the CB of the core-shell system due to widening of quantum confinement effect. With holes remaining confined to the core due to a large offset in the valence band (VB), we record the topography of the core-shell nanocrystals by probing their CB and VB edges separately. The topographies recorded at different temperatures representing wave-functions of electrons and holes corresponded to the results obtained from the DOS spectra. The results evidence temperature-dependent wave-function delocalization of one-type of carriers up to the shell layer in core-shell nano-heterostructures.
5 citations
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TL;DR: In this article, self-assembled InN dots were fabricated on GaN using 4H-SiC(0001) vicinal substrates (4° off toward [11-20] ).
Abstract: We have fabricated self-assembled InN dots on GaN using 4H-SiC(0001) vicinal substrates (4° off toward [11–20]) The size and density of InN dots were well controlled by changing the deposition amount and the growth temperature of InN Atomic force microscope (AFM) observation revealed that the critical thickness of InN for 2D-3D transition was between 08 and 10 nm In addition, it was found that the InN dots were preferentially formed at the multistep edges on GaN Therefore, the preparation of periodic multistep structures on GaN is considered to be an effective way to obtain highly ordered self-assembled InN dot arrays
4 citations
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TL;DR: Colloidal indium nitride nanocrystals (InN NCs) are stable heavily-doped nanomaterials with as-prepared electron densities around 7.4 × 1020 cm-3, independent of size, making these attracti...
Abstract: Colloidal indium nitride nanocrystals (InN NCs) are stable heavily-doped nanomaterials, with as-prepared electron densities around ⟨Ne⟩ ∼ 7.4 × 1020 cm–3, independent of size, making these attracti...
4 citations
References
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TL;DR: In this article, the photochemical redox potential of one carrier, as a function of the size of the crystal, has been studied in the case of a small number of electrons.
Abstract: Large semiconductor crystals have intrinsic electronic properties dependent upon the bulk band structure. As the crystal becomes small, a new regime is entered in which the electronic properties (excited states, ionization potential, electron affinity) should be strongly dependent upon the electron and hole in a confined space. We address the possibility of a shift in the photochemical redox potential of one carrier, as a function of crystallite size. As a semiquantitative guide, one might expect a shift on the order of h2/8em*R2 due to the kinetic energy of localization in the small crystallite. We model the elementary quantum mechanics of a charged crystallite using (a) the effective mass approximation, (b) an electrostatic potential for dielectric polarization, and (c) penetration of the carrier outside the crystallite in a cases of small effective mass. Shifts of several tenths of an eV appear possible in crystallites of diameter 50 A. The carrier charge density reside near the crystallite surface if ...
1,406 citations
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01 Jan 1983
Abstract: Large semiconductor crystals have intrinsic electronic properties dependent upon the bulk band structure. As the crystal becomes small, a new regime is entered in which the electronic properties (excited states, ionization potential, electron affinity) should be strongly dependent upon the electron and hole in a confined space. We address the possibility of a shift in the photochemical redox potential of one carrier, as a function of crystallite size. As a semiquantitative guide, one might expect a shift on the order of h2/8em*R2 due to the kinetic energy of localization in the small crystallite. We model the elementary quantum mechanics of a charged crystallite using (a) the effective mass approximation, (b) an electrostatic potential for dielectric polarization, and (c) penetration of the carrier outside the crystallite in a cases of small effective mass. Shifts of several tenths of an eV appear possible in crystallites of diameter 50 A. The carrier charge density reside near the crystallite surface if ...
1,355 citations
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TL;DR: The optical properties of wurtzite-structured InN grown on sapphire substrates by molecular-beam epitaxy have been characterized by optical absorption, photoluminescence, and photomodulated reflectance techniques as discussed by the authors.
Abstract: The optical properties of wurtzite-structured InN grown on sapphire substrates by molecular-beam epitaxy have been characterized by optical absorption, photoluminescence, and photomodulated reflectance techniques. These three characterization techniques show an energy gap for InN between 0.7 and 0.8 eV, much lower than the commonly accepted value of 1.9 eV. The photoluminescence peak energy is found to be sensitive to the free-electron concentration of the sample. The peak energy exhibits very weak hydrostatic pressure dependence, and a small, anomalous blueshift with increasing temperature.
1,345 citations
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TL;DR: In this paper, the authors reviewed the development of indium nitride (InN) semiconductors from its evolution to the present day and discussed the most popular growth techniques, metalorganic vapor phase epitaxy and molecular beam epitaxy.
Abstract: During the last few years the interest in the indium nitride (InN) semiconductor has been remarkable. There have been significant improvements in the growth of InN films. High quality single crystalline InN film with two-dimensional growth and high growth rate are now routinely obtained. The background carrier concentration and Hall mobility have also improved. Observation of strong photoluminescence near the band edge is reported very recently, leading to conflicts concerning the exact band gap of InN. Attempts have also been made on the deposition of InN based heterostructures for the fabrication of InN based electronic devices. Preliminary evidence of two-dimensional electron gas accumulation in the InN and studies on InN-based field-effect transistor structure are reported. In this article, the work accomplished in the InN research, from its evolution to till now, is reviewed. The In containing alloys or other nitrides (AlGaInN, GaN,AlN) are not discussed here. We mainly concentrate on the growth, characterization, and recent developments in InN research. The most popular growth techniques, metalorganic vapor phase epitaxy and molecular beam epitaxy, are discussed in detail with their recent progress. Important phenomena in the epitaxialgrowth of InN as well as the problems remaining for future study are also discussed.
779 citations
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TL;DR: Wurtzite InN films were grown on a thick GaN layer by metalorganic vapor phase epitaxy as discussed by the authors, and growth of a (0001)-oriented single crystalline layer was confirmed by Raman scattering, x-ray diffraction, and reflection high energy electron diffraction.
Abstract: Wurtzite InN films were grown on a thick GaN layer by metalorganic vapor phase epitaxy. Growth of a (0001)-oriented single crystalline layer was confirmed by Raman scattering, x-ray diffraction, and reflection high energy electron diffraction. We observed at room temperature strong photoluminescence (PL) at 0.76 eV as well as a clear absorption edge at 0.7–1.0 eV. In contrast, no PL was observed, even by high power excitation, at ∼1.9 eV, which had been reported as the band gap in absorption experiments on polycrystalline films. Careful inspection strongly suggests that a wurtzite InN single crystal has a true bandgap of 0.7–1.0 eV, and the discrepancy could be attributed to the difference in crystallinity.
676 citations