W. V. Lundin

Surface-mode lasing from stacked InGaN insertions in a GaN matrix

We report surface-mode lasing in a structure with 12-fold stacked InGaN insertions in a GaN matrix without using of Bragg mirrors. At high excitation densities, one of the modes of the Fabry–Perot cavity formed by the GaN sapphire and the GaN air interfaces, shows a strong superlinear increase in intensity with excitation density rise. The possibility to reach surface lasing in a very low finesse microcavity is due to the ultrahigh material gain of the InGaN insertions. The strong modulation of the absorption-gain spectrum with increase in the excitation density results in a pronounced energy shift of the cavity modes. We found that the threshold excitation density is weakly affected by temperature up to 110 K, while increases at higher temperatures. This behavior is attributed to thermal evaporation of carriers from InN-rich nanodomains and is typical for quantum dot lasers.

X-ray determination of threading dislocation densities in GaN/Al2O3(0001) films grown by metalorganic vapor phase epitaxy

Densities of a- and a+c-type threading dislocations for a series of GaN films grown in different modes by metalorganic vapor phase epitaxy are determined from the x-ray diffraction profiles in skew geometry. The reciprocal space maps are also studied. Theory of x-ray scattering from crystals with dislocations is extended in order to take into account contribution from both threading and misfit dislocations. The broadening of the reciprocal space maps along the surface normal and the rotation of the intensity distribution ellipse is attributed to misfit dislocations at the interface. We find that the presence of a sharp AlN/GaN interface leads to an ordering of misfit dislocations and reduces strain inhomogeneity in GaN films.

Correlation of mosaic-structure peculiarities with electric characteristics and surface multifractal parameters for GaN epitaxial layers

The first successful results of the application of multifractal analysis to a quantitative description of mosaic-structure peculiarities, that are typical of a GaN epitaxial layer with hexagonal modification grown on (0001) sapphire substrates, have been obtained. The characteristic size of the mosaic structure has been measured to be 200-800 nm. The direct dependence of mobility on the multifractal parameters (the Renyi dimension or the self-organization degree and the order-degree index) of the surface topology of the mosaic structure has been observed for all GaN layers investigated.

MOVPE of device-oriented wide-band-gap III-N heterostructures

The paper reviews metal-organic vapor phase epitaxy (MOVPE) of some key elements of III-N devices: InGaN quantum wells, InGaN/GaN and Al(Ga)N/GaN short-period superlattices, AlGaN/GaN and InAlN/GaN distributed Bragg reflectors. It is demonstrated that interaction of III-N materials with hydrogen is one of the key processes in MOVPE of these materials. Depending on the desired structure, this process may be fruitfully used or should be suppressed by the proper adjustment of reactor conditions.

A monolithic white LED with an active region based on InGaN QWs separated by short-period InGaN/GaN superlattices

A new approach to development of effective monolithic white-light emitters is described based on using a short-period InGaN/GaN superlattice as a barrier layer in the active region of LED structures between InGaN quantum wells emitting in the blue and yellow-green spectral ranges. The optical properties of structures of this kind have been studied, and it is demonstrated that the use of such a superlattice makes it possible to obtain effective emission from the active region.

Active region based on graded-gap InGaN/GaN superlattices for high-power 440- to 470-nm light-emitting diodes

The structural and optical properties of light-emitting diode structures with an active region based on ultrathin InGaN quantum wells limited by short-period InGaN/GaN superlattices from both sides have been investigated. The dependences of the external quantum efficiency on the active region design are analyzed. It is shown that the use of InGaN/GaN structures as limiting graded-gap short-period superlattices may significantly increase the quantum efficiency.

Effect of strain relaxation on active-region formation in InGaN/(Al)GaN heterostructures for green LEDs

Processes of active-region formation for green LEDs on the basis of multilayer strained InGaN/GaN nanoheterostructures have been studied. It is shown that the formation of structures of this kind is highly affected by elastic stress relaxation leading to a larger amount of indium incorporated into InGaN layers. For structures emitting in the blue spectral range, an increase in the number of quantum wells (QWs) from 1 to 10 does not lead to stress relaxation or to a shift of the emission wavelength, whereas for structures emitting in the green spectral range, raising the number of QWs from one to five causes a monotonic increase in the emission wavelength.

Effect of carrier gas and doping profile on the surface morphology of MOVPE grown heavily doped GaN:Mg layers

Magnesium is the only acceptor impurity practically used in MOCVD of GaN. High activation energy requires high impurity concentration, which results in epilayer morphology degradation. In the presented paper an influence of growth regimes, including choice of carrier gas, on GaN:Mg morphology is presented. It is demonstrated that surface morphology depends on an average magnesium concentration and strongly improves with using nitrogen as carrier gas.

Group-III-nitride-based light-emitting diode on silicon substrate with epitaxial nanolayer of silicon carbide

A light-emitting diode (LED) structure based on group III nitride has been grown for the first time on Si(111) substrate with SiC buffer nanolayer (50- to 200-nm-thick) obtained by solid-phase epitaxy. This LED structure is characterized by record low (<108 cm−2) density of lattice misfit dislocations at a total dislocation density of ∼8 × 108 cm−2. The photo- and electroluminescence spectra of obtained structures have been measured.

Blackbody-like emission of terahertz radiation from AlGaN/GaN heterostructure under electron heating in lateral electric field

The authors report on the observation and study of terahertz radiation emission from modulation-doped AlGaN/GaN heterostructure under conditions of heating of a two-dimensional electron gas in the lateral electric field. The experimental results are compared with the theoretical model of blackbody-like emission from hot two-dimensional electrons. Complementary transport measurements and a theoretical simulation were carried out to determine the dependence of effective electron temperature on electric field. The role of nonequilibrium optical phonon accumulation is discussed.