M. N. Mizerov

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.

A study of thermal processes in high-power InGaN/GaN flip-chip LEDs by IR thermal imaging microscopy

Results of an experimental study of temperature fields generated in high-power AlGaInN heterostructure flip-chip light-emitting diodes (LEDs) via their self-heating at high working currents are presented. The method of IR thermal imaging microscopy employed in the study enables a direct measurement of the temperature distribution over the p-n junction area with a high resolution of ∼3 μm at an absolute measurement error of ∼2 K. It is shown that large temperature gradients may arise in high-power LEDs at high excitation levels as a result of current crowding. This effect should be taken into account when designing lightemitting chips and estimating the admissible operation modes. The method of IR thermal imaging microscopy can also reveal microscopic defects giving rise to current leakage channels and impairing device reliability.

Optimization of the parameters of HEMT GaN/AlN/AlGaN heterostructures for microwave transistors using numerical simulation

The numerical simulation, and theoretical and experimental optimization of field-effect microwave high-electron-mobility transistors (HEMTs) based on GaN/AlN/AlGaN heterostructures are performed. The results of the study showed that the optimal thicknesses and compositions of the heterostructure layers, allowing high microwave power implementation, are in relatively narrow ranges. It is shown that numerical simulation can be efficiently applied to the development of microwave HEMTs, taking into account basic physical phenomena and features of actual device structures.

Photovoltaic converters of concentrated sunlight, based on InGaAsP(1.0 eV)/InP heterostructures

Results obtained in the development of a metal-organic vapor-phase epitaxy (MOVPE) technology and in studies of the electrical parameters of photovoltaic converters based on heterostructures in the InP/InGaAsP system for the spectral range 0.95–1.2 μm are presented. A MOVPE technique is developed for obtaining and doping InGaAsP solid solutions around the spinodal dissociation region with a band-gap width of about 1.0 eV. Photovoltaic converters of 1000-× concentrated sunlight are fabricated.

MOVPE of III-N LED Structures with Short Technological Process

The paper presents results on optimizing the MOVPE technology of light-emitting diode (LED) structures in a Dragon-125 system to accelerate the technological cycle. Due to the high growth rate of GaN layers and optimization of the initial GaN growth phase, the total duration of the epitaxial process is reduced from 4 h 45 min to 2 h 44 min. The LED diode structures grown by this technique compare well in quality with LEDs grown by the standard method in the commercially available AIX2000HT system.

InAs/GaSb superlattices fabricated by metalorganic chemical vapor deposition

The possibility of fabricating InAs/GaSb strained-layer superlattices by metalorganic chemical vapor deposition has been experimentally demonstrated. The results of transmission electron microscopy and photoluminescence spectroscopy investigations showed that the obtained structures comprise an InAs?GaSb superlattice on a GaSb substrate consisting of 2-nm-thick InAs and 3.3-nm-thick GaSb layers.

Composite InGaN/GaN/InAlN heterostructures emitting in the yellow-red spectral region

The results of studies of the properties of composite InGaN/GaN/InAlN heterostructures are reported. It is shown that, in the InAlN layer, there is substantial phase separation that brings about the formation of three-dimensional islands consisting of AlN-InAlN-AlN regions. The dimensions of these islands depend on the thickness of the InAlN layer and the conditions of epitaxial growth. Interruptions in the growth of InAlN provide a means for influencing the structural properties of the InAlN islands. The use of composite InGaN/GaN/InAlN heterostructures, in which the InGaN layer with a high In content serves as the active region in light-emitting diode structures, makes it possible to achieve emission in the yellow-red wavelength range 560–620 nm.

Fabrication and study of p-n structures with crystalline inclusions in the space-charge region

A new model of connecting elements for monolithic multijunction solar cells based on III–V compounds is proposed, in which p-n junctions with crystalline inclusions of a foreign semiconductor material in the space-charge region are used instead of p++-n++ tunnel junctions. The study shows that the introduction of crystalline inclusions to the space-charge region of the p-n junction in a GaSb-based structure allows current densities of ∼50 A/cm2 at an ohmic loss of ∼0.01 Ω cm2. The obtained characteristics of the connecting elements with crystalline inclusions show their applicability to multijunction solar cells for concentrated light conversion.

InGaN/GaN heterostructures grown by submonolayer deposition

InGaN/(Al,Ga)N heterostructures containing ultrathin InGaN layers, grown by submonolayer deposition are studied. It is shown that significant phase separation with the formation of local In-enriched regions ∼3–4 nm in height and ∼5–8 nm in lateral size is observed in InGaN layers in the case of InGaN and GaN growth by cyclic deposition to effective thicknesses of less than one monolayer. The effect of growth interruption in a hydrogen-containing atmosphere during submonolayer growth on the structural and optical properties of InGaN/(Al,Ga)N heterostructures is studied. It is shown that these interruptions stimulate phase separation. It is also shown that the formation of In-enriched regions can be controlled by varying the effective InGaN and GaN thicknesses in the submonolayer deposition cycles.