InAsN Quantum Dots Research Articles

Electron Emission Properties of Nitrogen-Induced Localized Defects in InAsN/GaAs Quantum Dots

The electron-emission properties of nitrogen-induced (N-induced) localized defects in InAsN/GaAs quantum dots (QDs) are investigated in detail by capacitance–voltage (C–V) profiling and bias-dependent deep-level transient spectroscopy (DLTS). The incorporation of nitrogen (N) into InAs QDs is shown to produce localized defects near QDs and threading-dislocation-related defects in the top GaAs layer. The threading dislocation is associated with an electron-emission energy of approximately 0.648 eV and emission from the sample surface toward the QDs. The electron-emission energy from the QDs associated with the localized defects increases from 0.19 to 0.36 eV, indicating that both types of defect near QDs have low electron emission energies. Therefore, the change in emission energy is attributable to the defects across the QD interface where a band offset exists. The C–V profile at 300 K shows extended carrier depletion near the QDs. As ac frequency increases, an electron-emission peak emerges at the QDs; this peak is followed by another prominent peak, suggesting that the localized defect that is responsible for this latter peak has an energy below the QD electron ground state. On the basis of a C–V profile simulation, this defect is located at the QD at the observed emission energy below the GaAs conduction band, 360 meV. A comparison with InAsN QD and strain relaxation InAs QD samples reveals that the localized defect arises from a nitrogen alloy fluctuation in the QD. The energy location of this defect reveals a possibility that incorporated N is associated with a particular mode.

Tailoring opto‐electronic properties of small InAsN and InN quantum dots

AbstractElectronic energy level structure (ELS), charge and spin density distributions (CDD and SDD, respectively) of small indium nitride clusters have been studied by means of the first‐principle, many‐body field theoretical methods. Electron charge delocalization due to charge accumulation on nitrogen and dopant nickel atoms, and resulting violation of the octet rule of the valence theory, have been observed. This charge delocalization mechanism provides for minimization of the total cluster energy, and thus is necessary to stabilize small non‐stoichiometric indium nitride systems. It may be used to manipulate opto‐electronic properties of indium nitride clusters, and also to synthesize novel, indium nitride‐based nanostructures with desirable properties (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Magneto-optic properties of InAsN and InN quantum dots doped with Co or Ni atoms

The electron energy level structure and charge and spin distributions of small InN and InAsN quantum dots (QDs) doped with Co or Ni atoms were studied using first-principle quantum many body field theoretical methods. In agreement with existing experimental findings, the obtained results show that nitrogen atoms in the studied small QDs accumulate the electron charge. It was also found that nickel atoms orchestrate electron charge redistribution necessary to stabilize such small systems.

Inhibition of In desorption in diluted nitride InAsN quantum dots

The effect of low N-alloying on the structure of capped InAs/GaAs quantum dots is analyzed by transmission electron microscopy related techniques. A statistical study of interplanar distances in InAsN quantum dots shows an increase in the lattice parameter compared to the InAs case. We suggest that the addition of nitrogen blocks the Ga/In exchange processes during the quantum dot capping process, leading to an In enrichment. The observed strong photoluminescence redshift of InAsN structures must therefore be attributed not only to the effect of nitrogen in the band gap, but also to a minor depletion of indium during the capping process.

Effect of nitrogen on the InAs/GaAs quantum dot formation

AbstractWe studied the influence of nitrogen incorporation on the InAsN/GaAs quantum dot formation using cross‐sectional scanning tunneling microscopy. Upon nitrogen exposure during InAs growth, rather strong dissolution effects occur, leading to the formation of extended almost spherical InGaAs quantum dots with a low indium content and almost free of nitrogen. In this paper we will discuss in particular the detailed stoichiometry determination of the quantum dots. Furthermore, we will demonstrate that nitrogen atoms are located in the surrounding GaAs matrix.Indium atoms are found underneath the nominal base plane, where quantum dot growth started, demonstrating strong strain‐induced intermixing already during quantum dot formation. The observed strong separation of indium and nitrogen is related to a rather low solubility of nitrogen within InAs as compared with GaAs. Finally, a schematic model for the growth of InAs and InAsN quantum dots in GaAs will be discussed in detail (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Dependence of N incorporation into (Ga)InAsN QDs on Ga content probed by rapid thermal annealing

AbstractIn this letter we demonstrate that the N incorporation into (Ga)InAsN quantum dots (QDs), grown on GaAs (100) by radio‐frequency (RF) plasma assisted molecular beam epitaxy (MBE), is enhanced as the Ga content increases up to 30% and decreases for Ga contents higher than 30%. Thus, this effect exhibits a maximum N incorporation with a Ga content of 30%. Two sets of (Ga)InAsN QDs samples have been grown under the same growth conditions but with different N contents in one of them and with different Ga concentration in the other set. Optical analysis using Photoluminescence (PL) measurements of the as‐grown and post growth rapid thermal annealed samples have been performed. The experimental results show a clear increase of the blueshift with the N concentration as occurred in dilute nitride quantum well (QW) structures. PL peak emission wavelength as high as 1.55 μm has been obtained from QDs capped with GaAs. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The influence of substrate temperature on InAsN quantum dots grown by molecular beamepitaxy

The effect of substrate temperature,390–480 °C, during molecular beam epitaxy growth of InAsN quantum dots has beenstudied. The quantum dot formation was studied in situ, and it is shownthat the quantum dots are close to fully relaxed within 4 monolayers (ML) ofInAsN deposition. Further, the indium concentration was estimated to be 84%,67%, 55% and 31% for 4 ML thick quantum dots grown at 390, 420, 450 and480 °C, respectively. Thus, Ga incorporation was demonstrated at all substratetemperatures. The dot diameter and height increased from 23 to 38 nm, and 2.5 to8.9 nm, respectively, when the growth temperature was increased from 390 to480 °C. The 5 K photoluminescence intensity and wavelength both increased with substratetemperature.

Analysis of InAsN quantum dots by transmission electron microscopy and photoluminescence

Quantum dots (QDs) have great potential in optical fiber communication applications were widely recognized. The structure of molecular beam epitaxy (MBE) grew InAsN QDs were investigated by transmission electron microscopy (TEM) and measured their optical properties by photoluminescence (PL). TEM images show that the InAsN QDs are irregular or oval shaped. Some of the InAsN QDs are observed to have defects, such as dislocations at or near the surface in contrast to InAs QDs, which appear to be defect free. PL results for InAsN QDs showed a red-shifted emission peak. In addition, the InAsN emission peak is broader than InAs QDs, which supports the TEM observation that the size distribution of the InAsN QDs is more random than InAs QDs. The results show that the addition of nitrogen to InAs QDs leads to a decrease in the average size of the QDs, bring changes in the QD's shape, compositional distribution, and optical properties.

Nitrogen-induced intermixing of InAsN quantum dots with the GaAs matrix

We investigated the influence of nitrogen incorporation on the growth of InAsN∕GaAs quantum dots (QDs) using cross-sectional scanning tunneling microscopy. Nitrogen exposure during InAs growth leads to a rather strong dissolution and the formation of extended almost spherical InGaAs QDs with a very low nitrogen content. Nitrogen atoms are instead observed in the surrounding GaAs matrix, and indium atoms are even found underneath the nominal base plane of the QDs. These effects are related to a rather low solubility of nitrogen within InAs, leading to high strain between indium-rich QDs and the surrounding nitrogen-rich matrix.

MOVPE growth and photoluminescence properties of InAsN QDs

AbstractThe self‐assembled InAsN quantum dots (QDs) were grown on the GaAs (001) substrates by MOVPE using 1,1‐dimethylhydrazine (DMHy) as the N precursor, and their photoluminescence (PL) properties were investigated. The N incorporation leads to a decrease in the QDs size for an equivalent amount of source supply due to the increase in the wetting layer thickness. It also leads to an increase in the QDs density which is interpreted by the reduced surface migration length. The PL from the electron ground state of the InAsN QDs clearly shows the red‐shift to 1159 nm by the N incorporation, indicating that the effect of the huge bandgap bowing is dominant over the quantum size effect in the InAsN QDs. The thermal activation energy of the QDs derived from the temperature dependence of the integrated PL intensity decreases from 176 meV to 140 meV by the DMHy supply, which is explained by the lowering of the electron quantum state of the thicker wetting layer caused by the N incorporation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The effect of rapid thermal annealing on the photoluminescence of InAsN/InGaAs dot-in-a-well structures

The effect of post-growth rapid thermal annealing on the optical characteristics of InAsN/InGaAs dot-in-a-well DWELL structures grown by molecular beam epitaxy on GaAs(1 0 0) has been studied. InAs/InGaAs DWELL structures have been used as a reference. Photoluminescence measurements of these samples show similar optical effects, such as a blueshift of the peak wavelength and a reduction of the full width of at half maximum PL emission, in both types of structures up to an annealing temperature of 750 °C. Nevertheless, at 850 °C, these effects are much more pronounced in the structures with N. These results suggest that an additional As–N interdiffusion process inside the InAsN quantum dots plays a dominant role in these effects at high annealing temperatures (850 °C) on InAsN/InGaAs structures.

The effect of nitrogen pressure during molecular beam epitaxy growth of InAsN quantumdots

The influence of N flux during molecular beam epitaxy growth of InAsN quantum dots wasstudied. Growth of InAsN dots under high N flux was shown to give rise to an abnormalgrowth behaviour compared to InAs dots and InAsN dots with lower nitrogen content. CubicInxGa1−xN (x = 0.21 ± 0.01)crystallites were found in samples grown with an excessive N flux. The crystallites are likely to form∼0.6 monolayers (MLs) after the quantum dots have nucleated, when the quantum dot changesgrowth mode. In addition, it is shown that a bimodal size distribution of InAsN quantumdots was generated in the wetting layer during the dot growth, as opposed to nucleation atN-induced dislocations at the substrate surface. The bimodal distribution may be explainedby an increased energy barrier, in the presence of nitrogen, for atomic incorporation intothe dots.

The effect of the individual species of the N plasma on the characteristics of InAsN quantum dots grown by MBE

The influence of the different species which constitute N plasma, such as atomic nitrogen, diatomic nitrogen and ionized species, on the morphological and optical characteristics of the InAsN quantum dots (QDs) has been studied in this work. We have performed several sets of growths modifying in each one the concentration of these species. Atomic force microscopy (AFM) and photoluminescence (PL) techniques have been used to perform the surface characterization and the optical analysis of these samples, respectively. Clearly, we have found a strong correlation between the structural and optical characteristics of the InAsN QDs with the plasma composition used during the growth. Ionized species favour the high density of QDs, atomic nitrogen increase dimensions of the QDs and molecular nitrogen does not almost affect the characteristics of these nanostructures. An increment of ionized species in the plasma yields a higher density of QDs, an increase in the atomic nitrogen increases the dimensions of the QDs and the molecular nitrogen flux used does not almost affect the characteristics of these nanostructures. Also, we have found that there is not redshift of the peak wavelength of the PL emission as we increase the atomic nitrogen concentration during the growth. This may be due to equal nitrogen incorporation into the quantum dots. We supposed that the mechanism dominating in it is possible that the nitrogen incorporation in these types of nanostructures depend on another growth parameter.

InAsN quantum dots grown on GaAs(001) substrates by MOVPE

The self-assembled InAsN quantum dots (QDs) were grown on the GaAs (001) substrates by MOVPE using 1,1-dimethlhydrazine (DMHy) and tertiarybutylarsine (TBAs) as the N and As precursors, respectively. The size distribution of the InAs(N) QDs grown at 450 °C and 420 °C is found bimodal. The InAsN QDs are typically 4-11 nm in height and 30-41 nm in width. The N incorporation into InAs induces the decrease of the QDs size, due to the increase of the wetting layer thickness. The density of the InAsN QDs with a nominal source supply of 2.6-3.0 ML, increases from 1.1-1.3×1010 cm–2 for the 450 °C growth to 2.1-2.3×1010 cm–2 for the 420 °C growth. The photoluminescence peaks (at 300 K) of the InAs(N) QDs grown at both temperatures clearly show a red-shift to 1200 nm by N incorporation. This red-shift is in contrast with the blue-shift expected from the decrease in the dot sizes (quantum size effect), indicating the huge bandgap bowing induced by N incorporation is dominant over the quantum size effect. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Photoluminescence from InAsN quantum dots embedded in GaInNAs/GaAs quantum wells

Photoluminescence (PL) from InAsN quantum dots embedded in a GaInNAs/GaAs quantum well (QW) has been investigated at low excitation conditions in the temperature range of 15–305 K. A very efficient emission at 1.3 μm with a small spectral broadening (30 meV) has been observed at room temperature for this system. The emission intensity decreases by only two decades in the whole investigated temperature range. Carrier escape into the states of the surrounding QW has been recognized as the main PL thermal quenching mechanism and the possible quenching via defect states has appeared to be negligible in this regime of excitation.

Contactless electroreflectance investigation of energy levels in a 1.3μm emitting laser structure with the gain medium composed of InAsN quantum dots embedded in GaInNAs∕GaAs quantum wells

Laser structures designed for the emission at 1.3μm and based on an active region containing InAsN quantum dots (QDs) embedded in GaInNAs∕GaAs quantum wells (QWs) have been investigated by contactless electroreflectance. Optical transitions related to both the dots and the wells have been observed and the energies of the latter have been calculated using the effective mass approach. It has been shown that QW confines one electron, one light-hole, and three heavy-hole states only and the energy separation between the QD and QW ground state transitions is approximately 250meV, which is ten times higher than the thermal energy at room temperature.

Growth and optical characterization of InAsN quantum dots

AbstractSelf‐assembled InAsN quantum dots (QDs) have been grown by rf‐plasma‐assisted molecular beam epitaxy (RF‐MBE) on GaAs(001) substrates via a 2‐monolayer (ML)‐thick InAs wetting layer. The InAsN QDs are typically 30–70 nm in diameter and 3–7 nm in height. The dot density was 3.6 × 109–2.3 × 1010 cm–2 for the fluxes corresponding to the nominal thicknesses of 3.0–4.0 MLs. As the nominal thickness increases, the dot density increases, while the diameter decreases. The low‐temperature (10 K) photoluminescence (PL) of the QD samples shows emission spectra in the wavelength range of 1.2–1.6 μm apparently caused by the N incorporation (0.8–2.0%) into the QDs. The QD size distribution causes broad emission spectra. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Study of InAsN quantum dots on GaAs substrates by molecular beam epitaxy

InAsN QDs on (001) GaAs substrates were studied. Each InAsN QD was surrounded by four {011} facets and had a pyramidal shape. However, InAs QDs had a half sphere shape. The InAsN QDs had size distributions with two maxima. This might be explained by the existence of very stable {011} facets and curved surfaces between the {011} facets. The curved surfaces act as the incorporation sites to grow the QD larger. This means that large InAsN QDs will be suppress the further growth, because of the smaller occupations of the curved surfaces to the total surface area of the InAsN QD. Excess In atoms supplied on the {001} plane will accumulate strains and form new small QDs by the Stranski-Krastanow (S-K) growth mode. This turns out two maxima of the size distribution. These results will open the possibility of obtaining the size control and small distributions of the InAsN QDs. We investigated the emission properties of these InAsN QDs. An emission peak of nearly 1300 nm from the InAsN QDs with a plasma power of 350 W was observed. InAsN QDs are an attractive material for achieving emissions in the fiber-optic communication wavelengths.

Structural and photoluminescence studies of InAsN quantum dots grown on GaAs by MBE

The growth of self-organized InAs(N) quantum dots on GaAs by molecular beam epitaxy has been investigated. Photoluminescence (PL) and transmission electron microscopy (TEM) experiments have been carried out to determine the influence of the growth temperature and nitrogen plasma exposure on the optical and structural properties of the dots. At low growth temperature, in the 410–450 °C range, some nitrogen is found to be incorporated in the quantum dots. This incorporation does not significantly affect their shape but causes a red-shift of the PL emission. At higher temperature, 510 °C, a bimodal distribution rapidly appears with nitrogen exposure. Cross-sectional TEM images reveal a first population of coherent dots whose shape is similar to that of InAs dots, and a second population of large, flat and occasionally relaxed dots; in that case the associated PL spectrum is typical of low density arrays of N-free InAs quantum dots. Discussion focuses on the different mechanisms involved in the dots growth. It is proposed that the occurrence of the second population of large dots is due to the defects and composition fluctuations induced by nitrogen at 510 °C.

Studies on single- and multi-layer InAsN quantum dots grown by solid-source molecular beam epitaxy

InAsN quantum dots were grown on GaAs (0 0 1) substrate by a solid-source molecular beam epitaxy system equipped with a radio-frequency nitrogen plasma source. The quantum dot formation was confirmed by reflection high-energy electron diffraction observation and atomic force microscopy measurement. Dot density as high as ∼1×10 11 cm −2 was achieved. Low-temperature and room-temperature photoluminescence measurements were carried out to investigate the optical property of the quantum dots. Multilayer quantum dot structures were found to shift the photoluminescence emission peak to longer wavelength from 1025 to 1120 nm.