The analysis of modern reference data for AlN, InN, GaN parameters and characteristics in comparison with GaAs ones for investigation of realization perspectives of devices on space charge waves was carried out in the work.
S.A. Sergeev, A.I. Mikhailov, O.S. Senatov, B.V. Sergeeva
Memoirs of the Faculty of Physics 2014. N 2.
Some results of theoretical investigation of the influence of diffusion and frequency dispersion of electrons differential mobility on the phase velocity of space-charge waves propagating in drift beam of electrons in semiconductor structures of indium nitride, gallium nitride and aluminum nitride are given in the paper
On the basis of measurement of thermal characteristics on 30 sampels of power InGaN/GaN light emitting diodes (LED) of Cree production of in the range of current 50... 550 mА it is shown that thermal resistance junction-case of all LEDs increases with increase of working current. It is established that the steepness of current dependence of consid-erably decreases at currents more than 300 mА. Selective parameters of current de-pendences are calculated. The received results confirm adequacy of early offered nonlinear thermal models of power LED and can use for an estimating of heterogeneity of distribution of temperature and current density in LED's structures.
The nanotemplet technology of «SiO2 - initiation layer Al2O3 - III-nitride» on silicon substrates for non-polar III-nitride heterostructures by gas-phase deposition using organometallic compounds in the formation of GaN/InGaN quantum wells, provides the formation of arrays of GaN-InGaN nanodots and nanorings on GaN nanorods. This ensures low dislocation density, ~ 3 × 106 cm-2, the increase in the photoluminescence intensity order of magnitude compared with flat patterns and the possibility of obtaining a higher concentration of indium in the solid solution InGaN
In the present research we optimize the design of light emitting diode module, produced using «chip-on-board» (COB) technology to reduce light energy losses in elements of module. Optimization was performed using numerical simulation and experimental research of COB samples. The influence of the encapsulating cover shape, reflecting substrate type, as well as the number, size and location chips were investigated. The optimal combination of the reflecting substrate type and the encapsulating cover shape allowing to maximize light output was identified. The work demonstrated the possibility of numerical simulations to optimize the design of LED modules without making expensive experimental samples.
Lamkin Ivan Anatolevich
Tarasov Sergey Anatolevich
Kurin Sergey Yurevich
Memoirs of the Faculty of Physics 2014. N 2.
AlGaN material system with the maximum band gap energy of 6.1 eV allows to manufacture ultraviolet (UV) optoelectronic devices working within a wide UV-A, B, C spectral range with a minimum wavelength of 210 nm. However, fabrication of the low-resistance ohmic contact to AlxGa1-xN with a high Al content (x > 0.5) is a difficult and actual task.
The best results on the AlGaN-based Schottky-type photodetectors were obtained by using Au (15nm) and Ti/Al (15/35nm) as barrier and ohmic contacts, respectively. The sequential short-wavelength shift of the photo-response curves toward deep UV (solar-blind) range with the minimum achieved cut-off wavelength less than 250 nm was observed for the structures with a Al-content as high as x = 0.6.
The article deals with power white light emitting diodes and modules characteristics investigation. This work actuality is caused by sweeping development of white light emitting diodes technology with a result that these devices are actually being concerned as a substitution of currently used light source – discharge lamps and incandescent bulbs. Different white light emitting diode and module samples spectral dependencies are presented in the article, luminous flux and light efficiency curves versus current are given, short results analysis is described.
The tests show that the method of chloride-hydride epitaxy allows you to create high quality emitting heterostructure. The characteristics of such emitters are comparable with the parameters of structures grown by chemical vapor deposition of metal-organic compounds. When an operating current of 20 mA temperature tj of the active region was 43oC, optical output power and efficiency - 1.14 mW and 1.46%, respectively. UV LEDs are efficient in continuous drive mode up to the value of the forward current 135 mA.
Results demonstrating possibilities of scanning electron microscopy methods for a characterization of GaN and GaN based light emitting structures are presented. Methods for correct excess carrier diffusion length measurementы in the structures with the small diffusion length are discussed. It is shown that the Electron Beam Induced Current (EBIC) method allows not only to measure the diffusion length in GaN films but in some cases to reconstruct also the lateral donor center distribution with a spatial resolution in the micrometer range. It is shown experimentally that in the structures with the small diffusion length the lateral resolution under extended defects revealing can be about 100 nm or even better. It is shown that channels of enhanced minority carrier transport across the active region of light emitting structures with InGaN/GaN quantum wells can be revealed by the EBIC.
A self-structuring of the surface of silicon wafers under specific annealing conditions is reported on. This effect can be used for developing new maskless methods of the fabrication of structured silicon substrates, which are prospective for the use in the technology of light-emitting diodes based on gallium nitride and III–nitride solid solutions.
A direct correlation is found between efficiency droop and changes in the high energy side of emission spectrum of InGaN/GaN quantum wells (QWs) with increasing current density. A dynamic model of energy relaxation of injected carriers in exponential band tails of InGaN QWs is proposed. At low injection level the carriers trapped by shallow tail states quickly hop directly to lower-energy tail states. This results in the strong carrier localization and high-energy cutoff of emission spectrum. At higher injection level hopping directly to deeper states is suppressed due to the partial filling of tail states. As a result the ratio of mobile to localized carriers increases with current. The emission efficiency decreases because of the enhancement of lateral diffusion length, carrier capture by defects and tunnel-recombination leakage via defects. Simultaneously the high-energy cutoff of emission spectrum shifts to higher energy. Thus, the magnitude of efficiency droop is directly related to the relative broadening of emission spectrum.
Capacitance-frequency and conductance-frequency dependences for InGaN/GaN multiple-quantum-well light-emitting structures are investigated at wide ranges of temperature and bias voltage. The charge relaxation in a quantum well is found to be satisfactorily described by two emission processes with different dependences of emission rate on temperature. It is shown that in typical InGaN/GaN light-emitting structures, one or a few quantum wells can be filled with electrons even for the relatively high reverse biases applied to the structure and contribute to the measured capacitance. This allows to explain the observed temperature and frequency dependences of apparent carrier concentration profiles obtained under capacitance—voltage profiling in these structures.
The growth of “thick" (200 nm) AlN layers on sapphire at 1150ºC using STE3N MBE system is shown to be the key step to obtain high quality GaN-based heterostructures. An appropriate sequence of AlGaN transition layers grown on such an AlN both allows to reduce dislocation density in GaN down to 9•108–1•109 cm–2 in comparison with GaN layers grown on “thin" (10 nm) low temperature AlN nucleation layer. Maximum electron mobility in 1.5 µm thick GaN silicon doped layer reaches 600–650 сm2/V.s at electron concentrations (3-5)•1016 cm–3.