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MOCVD-grown heterostructures with one or several In[sub x]Ga[sub 1-x]N layers in a GaN matrix have been studied by transmission electron microscopy. In heterostructures with thick InGaN layers, a noncoherent system of domains with lateral dimensions (∼50 nm) on the order of the layer thickness (∼40 nm) is formed. In the case of ultrathin InGaN inclusions, nanodomains coherent with the GaN matrix are formed. The content of indium in nanodomains, determined by the DALI method, is as high as x ≈ 0.6 or more, substantially exceeding the average In concentration. The density of the nanodomains formed in the structures studied is n ≈ (2-5) x 10[sup 11] cm[sup -2]. In the structures with ultrathin InGaN inclusions, two characteristic nanodomain sizes are observed (3-6 and 8-15 nm). [ABSTRACT FROM AUTHOR]

Double heterostructures AlGaN/GaN/AlGaN grown by hydride vapor phase epitaxy and designed for use as light emitting diodes for 360 nm wavelength were patterned by shallow nanoholes and injected with Ag/SiO2 or Al nanoparticles. A 1.8 times increase in the photoluminescence and microcathodoluminescence signal from the GaN active region was observed for 100 nm diameter Al nanoparticles, the efficiency decreased compared to the reference planar samples for small Al nanoparticles of 30-40 nm diameter, and a moderate increase of 1.2 times was detected for Ag/SiO2 nanoparticles. The observed phenomena are explained by the GaN emitter coupling with localized surface plasmons produced by metallic nanoparticles. (© 2015 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim) [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]

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 luminescence properties of a GaN/A1[sub 0.1]Ga[sub 0.9]N double heterostructure grown by vapor-phase deposition from organometallic compounds are studied. When luminescence is observed from the end, the radiation intensity shows a sharply defined threshold dependence on the pump density. The threshold excitation density at T = 77 K was ∼40 kW/cm² and the wavelength of the stimulated emission was λ = 357 nm. The long-wavelength shift of the emission line at high pump densities may be attributed to renormalization of the band gap caused by manyparticle interactions in the electron-hole plasma. [ABSTRACT FROM AUTHOR]