Search

we present the results of fabrication of flip-chip LEDs with removed substrate from AlInGaN heterostructures grown on SiC/Si substrates synthesized by vacancy-matching atom substitution. It is shown that SiC/Si substrates are optimal from the viewpoint of matching lattice parameters, thermal conductivity, and optical characteristics of the material at a significantly lower cost. Therewith, the procedure of cutting wafers into individual chips and removal of the opaque silicon part of the substrate becomes easier, and the transparent SiC part of the substrate remaining on the chip surface creates a relief that facilitates light output. [ABSTRACT FROM AUTHOR]

Light-emitting III–N heterostructures are grown by gas-phase epitaxy from organometallic compounds on SiC/Si (111) templates (substrates) formed using matched atomic substitution. Investigations of the optical and structural properties of heterostructures are carried out in order to reveal the formation of defects in the structures. It is shown that such heterostructures exhibit specific features of the growth of the (Al,Ga)N buffer layer associated with the presence of pores in Si under the SiC/Si interface. The use of an optimized buffer layer design makes it possible to significantly reduce the dislocation density and form an active region with good structural quality. [ABSTRACT FROM AUTHOR]

Under study is the photoluminescence of two types of MBE-grown heterostructures with quantum-confined InGaAsN/GaAs layers: (1) conventional InGaAsN quantum wells (QWs) in GaAs, and (2) heterostructures with an active region consisting of a short-period GaAsN/InGaAsN superlattice that has an InGaAsN QW with a submonolayer InAs insertion at its center. At room temperature, the structures under study emit light in the range from ∼1.3 to ∼1.55μm. In the second type of heterostructure, emission with a wavelength larger than 1.5μm can be obtained at lower nitrogen and indium concentrations than in a conventional QW. This leads to a significant depression of the effects related to decomposition of an InGaAsN solid solution, thus improving the radiative efficiency of the InGaAsN QWs. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

The optical properties of GaAsN/GaAs heterostructures grown by molecular-beam epitaxy with different nitrogen content in the layers have been studied. The optical properties of GaAsN layers in the growth conditions under study are defined by the carrier recombination via localized states related to a strong composition inhomogeneity in the solid solution. The increasing of the nitrogen content raises the composition inhomogeneity and the carrier localization energy. [ABSTRACT FROM AUTHOR]

A method is proposed for growing stacked InAs/InGaAs self-organized quantum dots on GaAs substrates. The technique allows fabrication of structures exhibiting intense and narrow-line photoluminescence in the 1.3 µm wavelength region. The influence of growth conditions on structural and optical characteristics was studied. The proposed structures show promise in developing vertical-cavity surface-emitting devices. [ABSTRACT FROM AUTHOR]

InGaN/GaN structures with dense arrays of InGaN nanodomains were grown by metallorganic chemical vapor deposition. Lasing in vertical direction occurs at low temperatures, indicating ultrahigh gains (∼10[sup 5] cm[sup -1]) in the active region. Fabrication of an effective AlGaN/GaN distributed Bragg reflector with reflectivity exceeding 90% enables vertical lasing at room temperature in structures with a bottom distributed Bragg reflector, despite the absence of a well-reflecting upper mirror. The lasing wavelength is 401 nm, and the threshold excitation density is 400 kW/cm². [ABSTRACT FROM AUTHOR]

Lasing is discovered in the direction perpendicular to the surface in quantum-size InGaN/GaN multilayer heterostructures grown by vapor-phase epitaxy. At high excitation densities one of the modes in the luminescence spectrum, which is modulated by modes of the Fabry-Pérot cavity formed by the GaN/air and GaN/sapphire-substrate interfaces, is sharply amplified and begins to dominate the spectrum. The dependence of the luminescence intensity on pump density has a clearly expressed threshold character. The threshold excitation density in the vertical direction is 5-6 times greater than the stimulated-emission threshold for observation from an end surface of the structure. The gain coefficient in the active region at the threshold for surface-emitting lasing is estimated as 2 × 10[sup 5] cm[sup -1]. The interaction between the cavity modes and the gain spectrum is detected in the form of displacement (by up to 2.6 nm) of modes on the short-wavelength edge of the luminescence spectrum toward higher photon energies. The characteristic temperature (T[sub 0]) measured in the range from 16 to 120 K is 480 K. At higher temperatures T[sub 0] = 70 K. [ABSTRACT FROM AUTHOR]

It is shown that the self-organization effects appearing during the N-cycle deposition of In[sub 0.5]Ga[sub 0.5]As(12 Å)/GaAs(50 Å) lead to the formation of ordered arrays of vertically coupled quantum dots (VCQD's). The optical properties are investigated as a function of the number of deposition cycles (N = 1-10). In cases of injection heterostructure lasers with an active region based on VCQD's it is shown that increasing the number N of deposition cycles from 1 to 10 makes it possible to lower the threshold current density at 300 K from 950 to 97 A/cm² and to achieve a continuous lasing regime at room temperature with an output power of 160 mW per mirror. [ABSTRACT FROM AUTHOR]

One of the main factors that limit the maximum attainable efficiency of InGaAlN-based light-emitting diode (LED) structures grown on standard sapphire substrates is the low efficacy of extracting light from devices. A promising solution of this problem consists in using specially profiled (patterned) sapphire substrates. A method for the formation of a special surface microrelief on the sapphire substrates is described. The properties of GaN epilayers and InGaAlN-based LED heterostructures grown on such substrates are presented. [ABSTRACT FROM AUTHOR]

The behavior of threading dislocations in AlGaN and InGaN layers incorporated into GaN-based heterostructures is studied. It is shown that InGaN layers with an intermediate composition can be used as the most effective dislocation filters. Estimations of the stresses generated by dislocations and nanodomains show good agreement between the theory and experiment. [ABSTRACT FROM AUTHOR]

Specific features of MOCVD growth of AlGaN/GaN heterostructures have been studied. In the structures obtained, the 2D electron gas in the channel had a density of 1.2 × 1013cm–2 and a mobility of 1290 cm2/(V s) at room temperature. The effect of the purity of starting components on the properties of the structure is studied. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

Room-temperature photoluminescence (PL) at 1.55 µm from heterostructures with InAs/InGaAsN quantum dots (QDs) grown by MBE on GaAs substrates is demonstrated for the first time. The effect of nitrogen incorporated into InAs/InGaAsN QDs on the PL wavelength and intensity was studied. The integral intensity of PL from the new structure with InAs/(In)GaAsN QDs is comparable to that from a structure with InGaAsN quantum wells emitting at 1.3 µm. [ABSTRACT FROM AUTHOR]

The influence of different growth conditions on the In distribution in ultrathin InGaN insertions in a GaN matrix is investigated by high-resolution transmission electron microscopy and an appropriate image evaluation technique. It is demonstrated that the indium distribution represents dense arrays of In-rich nanodomains inserted in a layer with a lower indium concentration. The sizes of the In-rich regions are about 4-5 nm at a growth temperature of 720 °C. Increasing the growth temperature leads to a strong decrease in the of nanoisland density and, also, a moderate decrease in their lateral size. Increasing the trimethylindium/trimethylgallium ratio strongly increases the density of the islands, but the lateral size remains weakly effected. The observations are in agreement with a thermodynamic model of island formation including entropy effects. [ABSTRACT FROM AUTHOR]

The optical properties of multilayer structures with quantum dots in the heteroepitaxial InAs/GaAs system have been studied. The structures were obtained by the method of submonolayer migration-stimulated epitaxy. It is shown that the optimized growth conditions provide room-temperature luminescence at a wavelength of 1.3 µm. [ABSTRACT FROM AUTHOR]

It is shown that an array of two-dimensional islands is formed during the growth of ultrathin (∼1.5 monolayers) InSb layers on a GaSb (100) surface by molecular beam epitaxy. After the deposition of several InSb layers separated by narrow barriers, islands of subsequent rows are formed on top of islands of the first row (vertical correlation effect). The formation of islands is confirmed by analysis of the photoluminescence spectra. [ABSTRACT FROM AUTHOR]

Molecular beam epitaxy was used to fabricate GaAsN/GaAs and InGaAsN/GaAs heterostructures, and the influence of the growth regimes on their characteristics was studied. It is shown that implantation of nitrogen causes a substantial long-wavelength shift of the radiation. The possibility of obtaining 1.4 µm radiation at room temperature was demonstrated using In[sub 0.28]Ga[sub 0.72]As[sub 0.97]N[sub 0.03]/GaAs quantum wells. [ABSTRACT FROM AUTHOR]

Cyclotron resonance is measured in solitary type-II InAs-AlGaSb quantum wells grown by molecular-beam epitaxy under various growth conditions. Quantum oscillations observed in the cyclotron resonance spectra in InAs-GaSb samples are attributed to scattering by a shortrange potential due to roughness of the heterointerface. A new method based on measurement of the cyclotron resonance spectra is proposed for assessing the quality of the heterointerface. [ABSTRACT FROM AUTHOR]

InAs self-organized quantum dots in In[sub 0.53]Ga[sub 0.47]As and In[sub 0.52]Al[sub 0.48]As matrices have been grown on InP substrates by molecular beam epitaxy. The dot size in InGaAs has been found to be 3–4 times larger, but the areal density about an order of magnitude smaller than that in InAlAs. Low-temperature photoluminescence (PL) of the InAs/InGaAs quantum dots is characterized by a narrow (35 meV) PL line as compared to that of InAs/InAlAs quantum dots (170 meV). Quantum dot formation increases the carrier localization energy as compared to quantum well structures with the same InAs thickness in a similar manner for both InAs/InGaAs and InAs/InAlAs structures. The effect of the barrier band gap on the optical transition energy is qualitatively the same for quantum well and quantum dot structures. The results demonstrate a possibility of controlling the quantum dot emission wavelength by varying the matrix composition. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]