A. D. Bondarev

Investigations of nanodimensional Al2O3 films deposited by ion-plasma sputtering onto porous silicon

The purpose of this study is the deposition of nanodimensional Al2O3 films on the surface of nanoporous silicon and also fundamental investigations of the structural, optical, and morphological properties of these materials. Analyzing the results obtained here, it is possible to state that ultrathin nanostructured Al2O3 films can be obtained in the form of threads oriented in one direction and located at a distance of 300–500 nm from each other using ion-plasma sputtering on a layer of porous silicon. Such a mechanism of aluminum-oxide growth is conditioned by the crystallographic orientation of the initial single-crystalline silicon wafer used to fabricate the porous layer. The results of optical spectroscopy show that the Al2O3/por-Si/Si(111) heterophase structure perfectly transmits electromagnetic radiation in the range of 190–900 nm. The maximum in the dispersion of the refractive index obtained for the Al2O3 film grown on por-Si coincides with the optical-absorption edge for aluminum oxide and is located in the region of ~5.60 eV. This fact is confirmed by the results of calculations of the optical-absorption spectrum of the Al2O3/por-Si/Si(lll) heterophase structure. The Al2O3 films formed on the heterophase-structure surface in the form of nanodimensional structured threads can serve as channels of optical conduction and can be rather efficiently introduced into conventional technologies, which are of great importance in microelectronics and optoelectronics.

AlGaAs/GaAs diode lasers (1020–1100 nm) with an asymmetric broadened single transverse mode waveguide

Approaches to the development of laser heterostructures with a broadened single-mode waveguide are studied theoretically and experimentally. It is shown that the use of n- and p-type emitters with different refractive-index values ensures lasing in the fundamental mode only, if the thickness of the waveguide layer is 2 μm. The studied semiconductor lasers fabricated using the developed heterostructure feature internal optical losses amounting to 0.6 cm−1; the divergence in the plane perpendicular to the p-n junction is 23°. In the continuous lasing mode at room temperature, a linear power-current characteristic is obtained at an output optical power as high as 7 W.

Thermal delocalization of carriers in semiconductor lasers (λ = 1010–1070 nm)

The temperature dependences of the emission characteristics of semiconductor lasers based on MOVPE-grown asymmetric separate-confinement heterostructures (wavelengths λ = 1010–1070 nm) have been studied. It was found that, in the continuous-wave mode, the main mechanism of “saturation” of the light-current characteristic with increasing temperature of the active region is carrier delocalization into the waveguide layer. It was experimentally demonstrated that the thermal delocalization of carriers depends on the energy depth of the quantum well (QW) in the active region. It is shown that the minimum internal optical loss at 140°C is obtained in laser structures with the largest energy depth of the QW of the active region.

Structure and optical properties of thin Al2O3 films deposited by the reactive ion-plasma sputtering method on GaAs (100) substrates

Structural analysis and optical spectroscopy are used to study the properties of ultrathin Al2O3 films deposited in an ion-plasma sputtering installation. It is possible to demonstrate that the technological method used to deposit the films can yield amorphous, smooth, pore-free, and almost homogeneous films in which crystals of the α phase of aluminum oxide Al2O3 nucleate. The films transmit light extremely well in the IR (infrared), visible, and UV spectral ranges and are of potential importance for the development on their basis of antireflection coatings for mirrors of high-power semiconductor lasers based on III–V compounds.

Properties of AlN films deposited by reactive ion-plasma sputtering

The properties of SiO2, Al2O3, and AlN dielectric coatings deposited by reactive ion-plasma sputtering are studied. The refractive indices of the dielectric coatings are determined by optical ellipsometry. It is shown that aluminum nitride is the optimal material for achieving maximum illumination of the output mirror of a semiconductor laser. A crystalline phase with a hexagonal atomic lattice and oxygen content of up to 10 at % is found by transmission electron microscopy in the aluminum-nitride films. It is found that a decrease in the concentration of residual oxygen in the chamber of the reactive ion-plasma sputtering installation makes it possible to eliminate the appearance of vertical pores in the bulk of the aluminum-nitride film.

Quenching of lasing in high power semiconductor laser

Emission characteristics of high-power semiconductor lasers with a mesa-stripe design based on heterostructures with separate confinement are studied. It is shown that, in high-power semiconductor lasers with a mesa-stripe design, divergence of emission increases with the pump current as a result of generation of high order lateral optical modes. It is demonstrated that scattered radiation of high order lateral optical modes affects the transparency of passive regions outside the mesa stripe that forms a waveguide of the Fabry-Perot resonator. It is established that the transparency of passive regions results in fulfillment of threshold conditions for the closed optical mode in the semiconductor laser’s chip. As a result of generation of the closed optical mode in a cavity formed by four cleaved faces quenching of lasing modes in the mesa-stripe waveguide of the Fabry-Perot resonator occurs.

Selection of modes in transverse-mode waveguides for semiconductor lasers based on asymmetric heterostructures

Asymmetric Al0.3Ga0.7As/GaAs/InGaAs heterostructures with a broadened waveguide produced by the method of MOCVD epitaxy are studied. It is established that the precision shift of the active region to one of the cladding layers ensures the generation of the chosen mode of high order in the transverse broadened waveguide. It is experimentally established that this shift brings about an increase in internal optical losses and a decrease in the internal quantum efficiency of stimulated emission. It is shown experimentally that the shift of the active region to the n-type cladding layer governs the sublinear form of the power-current characteristic for semiconductor lasers; in the case of a shift of the active region towards the p-type cladding layer, the laser diodes demonstrated a linear dependence of optical power on the pump current in the entire range of pump currents.

On the temperature delocalization of carriers in GaAs/AlGaAs/InGaAs quantum-well heterostructures

The effect of temperature delocalization in semiconductor lasers (emission wavelength λ = 1060 nm) based on symmetric and asymmetric separate-confinement heterostructures fabricated by metal-organic vapor-phase epitaxy (MOVPE) is studied. Experimental and calculated estimates show that the carrier concentration in the waveguide increases by an order of magnitude when the temperature of a semiconductor laser is raised by ∼100°C. It is found that an increase in the temperature of the active zone leads to enhancement of the temperature delocalization of both electrons and holes. It is shown that the delocalization of holes begins at higher temperatures, compared with that of electrons. It is demonstrated experimentally that the onset of temperature delocalization depends on the threshold carrier concentration in the active region of a laser at room temperature. It is found that raising the energy depth of the active region by choosing the waveguide material makes it possible to fully suppress the temperature-delocalization process up to 175°C.

Diode lasers emitting at 1190 nm with a highly strained GaInAs quantum well and GaAsP compensating layers MOCVD-grown on a GaAs substrate

Laser heterostructures with an active region consisting of a highly strained GaInAs quantum well located between GaAsP compensating layers were grown by metal-organic chemical vapor deposition on GaAs substrates. Stripe mesa-structure laser diodes of 100 μm aperture emitting at 1190 nm were fabricated. The highest emission power of these diodes in the CW mode amounted to 4.5 W per output mirror. Due to the presence of compensating GaAsP barriers, the GaInAs quantum well remains unrelaxed, which eliminates the spread in the maximum emission power of laser diodes produced from the same heterostructure.

Double-band generation in quantum-well semiconductor laser at high injection levels

Spectral and emission-power characteristics of semiconductor lasers based on quantum-dimensional asymmetric heterostructures with separate confinement in a system of InGaAs/GaAs/AlGaAs alloys are studied in the case of high pump levels in the pulsed mode of lasing (200 A, 100 ns, and 10 kHz). It is shown that, in lasers with a quantum-dimensional active region containing one or two levels of dimensional quantization, the spectrum consists of one or two lasing bands. It is established that the condition for inverse population of the second electron level and two-band lasing are attained due to leveling-off of the rate of stimulated recombination from the first electron level and a high density of states for the second level. It is shown that, in lasers with double-band lasing spectrum, the total emission spectrum exceeds appreciably the emission power of a laser with a single electron level and a single spectral band.