Search

The principles of the linearization of the positional characteristics of magneto-optical displacement transducers are examined. Mathematical modeling of the positional characteristics is conducted, and results of pilot studies of prototypes of displacement transducers are presented.

We examine the design principles of the magneto-optical displacement transducers based on the Faraday effect. We present the results of mathematical modeling of the characteristics of such displacement transducers. The practical application of the obtained data is given.

We have studied the influence of conditions used for the growth of InGaN layers by the molecular beam epitaxy (with ammonia as a source of nitrogen) on the properties of GaN/InGaN heterostructures. It is established tat the temperature dependence of the critical flux of indium leading to the formation of droplets for the growth of InGaN on GaN is exponential and is determined by the enhanced desorption of indium from the surface of a growing layer with increasing substrate temperature. The growth of InGaN layers on GaN, even at the maximum possible flux of indium not accompanied by the droplet formation, leads to an extended profile of indium distribution in InGaN layers. It is shown that, in order to obtain sharp heteroboundaries and increase the content of indium in thin InGaN layers, it is necessary to create and maintain the so-called “wetting” film of metallic indium on the substrate surface prior to and in the course of InGaN layer growth. Using the obtained results, basic conditions are established for growing thin InGaN layers for the active elements of light-emitting devices operating in the blue-violet spectral range.

The effect of growth conditions (V/III ratio, substrate temperature) on the properties of materials in AlN-GaN systems is discussed. A concept of the growth of the AlN/AlGaN/GaN multilayer heterostructure, which provides the improvement of crystal quality and surface morphology of the layers, is suggested and realized. The improvement of the properties of GaN in the AlN/AlGaN/GaN/AlGaN multilayer heterostructure is confirmed by a considerable increase in electron mobility in the two-dimensional electron gas formed at the upper heterointerface GaN/Al0.3Ga0.7N.

High-power field-effect transistors (FETs) are among the main applications of heterostructures based on group III metal nitrides, which in most cases implement the classical GaN/AlGaN structure with a single junction. An alternative approach based on the use of double heterostructures with imporved two-dimensional electron gas (2DEG) confinement offers a number of advantages, but such structures are usually characterized by a lower carrier mobility and density (in GaN layers of reduced thickness) as compared to the values in the single-junction structures. Optimization of the heterostructure design and ammonia MBE growth conditions allowed us to obtain multilayer AlN/AlGaN/GaN/AlGaN heterostructures with quantum wells, which are characterized by a 2DEG carrier mobility of 1100–1300 cm2/(V s) and a sheet electron density of (1.1–1.3) × 1013 cm-2. Experimental FETs based on the obtained multilayer heterostructures in a static regime exhibit working current densities up to 0.6 A/mm at a transconductance of up to 150 mS/mm and a breakdown voltage above 100 V.

A concept for the design of experimental AlGaN/GaN/AlGaN double heterostructures with a two-dimensional electron channel are discussed, together with their main properties. The structures were formed by ammonia molecular-beam epitaxy on sapphire substrates. The foundations for postgrowth technology are developed for microwave field-effect transistors based on Group-III nitrides, including the formation of a mesa isolation and the preparation stage of nonrectifying contacts and the Schottky barrier. The first field-effect transistors fabricated based on the above heterostructures have a complete set of static characteristics and can operate in a mode of weak microwave signals at a frequency of 8.15 GHz.

The electrical properties of epitaxial InAs and solid solutions based on it (InGaAsSb, InAsSbP, InAsGa, InAsP) have been investigated. It is shown that intentionally undoped crystals have n-type conductivity, which is determined by shallow donor impurities (E 1=0.002–0.003 eV) and structural defects (E 2=0.02–0.03 eV and E 3=0.09–0.10 eV). It is shown that growth of epitaxial InAs using the neutral solvent Pb and also rare-earth elements makes it possible to reduce the electron density by almost an order of magnitude (to levels as low as 3×1015 cm−3) due to due to a decrease in the density of structural defects.

A study has been made of wavelength tuning in double heterostructure InAsSb/InAsSbP-based diode lasers. A simple mathematical model, which takes into account the spatially homogeneous injection and the dependence of the dielectric constant on the charge carrier density, is discussed. The wavelength can be increased or decreased, depending on the pump current and diode structure parameters, as is observed experimentally. The process of wavelength tuning proceeds with virtually zero delay time since it is determined by the photon lifetime in the cavity and in part by the lifetime of nonequilibrium charge carriers.

We report preliminary results on the transfer of the ammonia MBE technology of AlN/AlGaN/GaN/AlGaN heterostructures to silicon substrates. Optimization of the growth conditions allowed the number of macroscopic cracks in the epilayers to be reduced and ensured the growth of heterostructures with two-dimensional electron gas, which are suitable for the creation of field-effect transistors. The saturation current of prototype devices based on the heterostructures grown on silicon substrates are comparable with the analogous parameter of devices grown on sapphire and exhibits no decrease related to thermal scattering at high bias voltages.

New possibilities of scanning electron microscopy, using secondary-and reflected-electron signals, for determining the position of heteroboundaries in long-wavelength laser structures are reported. The formation of the indicated signals in structures of mid-infrared-range lasers of a new type based on type-II GaInAsSb/InGaAsSb heterostructures as well as in the conventional InAsSb/InAsSbP heterostructures is analyzed. The observed characteristic features of the formation of secondary-and reflected-electron signals in these structures as compared with the well-studied AlGaAs/GaAs structures are explained. The results obtained are necessary for accurate determination of an important laser parameter — the position of the p-n junction. It is shown that it is best to use the reflected-electron signal.

InAsSb-InAsSbP double heterostructures diode lasers for the spectral region 3.3 /spl mu/m grown by liquid phase epitaxy have been investigated. Emission spectra, far-field patterns and wavelength tuning have been studied over a wide current range from threshold value I/sub th/ up to 3I/sub th/ at the temperature of liquid nitrogen. Current-controlled wavelength tuning has been obtained both towards shorter wavelengths (to 4.56 cm/sup -1/) and towards longer wavelengths (up to 0.9 cm/sup -1/) at a temperature T=77 K, at lasing generation that maintains single mode. Comparison of the emission properties of lasers driven by different types of current (short pulse current, sawtooth pulse current and quasi-CW regime) showed the same quantum-mechanical nature of current tuning. A theoretical model of this nonlinear optical phenomenon is proposed. The estimated times of current tuning, defined mainly by the photon lifetime in the cavity, are about 10/sup -9/-10/sup -12/ s.

We have produced, by using liquid-phase epitaxy, 2.7 to 3.0-µm lasers based on InAsSbP double-heterostructures with different phosphorus contents in the active and wide-gap regions. The lasers possess threshold current density ∼0.8 kA/cm2 at 77 K and operate in the pulsed mode up to ∼124 K with maximum threshold current density 10–12 kA/cm2. The lasers have a low series resistance ∼0.45 Ω.

Diode lasers based on InAsSb/InAsSbP with separate electrical and optical confinement, emitting in the wavelength interval 3–4 µm, are investigated. The lasers attain a higher operating temperature when electrical confinement is created by means of type-II heterojunctions. Interface Auger recombination is suppressed in lasers of this type, and the experimental current density is close to the theoretically calculated value for the case of predominant volume Auger recombination at a temperature of 180–220 K.

InGaN/GaN heterostructures have been grown by molecular beam epitaxy (MBE) using ammonia as a source of nitrogen. The influence of the growth temperature and rate on the incorporation of indium into the epitaxial layers and the position of the corresponding photoluminescence peak has been studied. Based on these data, optimum growth conditions have been selected for the ammonia MBE of InGaN layers in the active region of light-emitting diodes operating in the blue/violet spectral range.

The experimental technology and characteristics of domestic AlGaN/GaN high electron mobility transistors are described. The results show good prospects for further development.

The lasing spectra and the shift in the position of the modes in the current range (1–5)I th with various methods of pumping the nonequilibrium charge carriers are analyzed. It is shown that the pumping method does not influence the character of the tuning of the radiation line. The large short-wavelength tuning range (up to 50 A) is due not to the heating of the crystal lattice in the active-region material but rather the nonuniform nonequilibrium charge-carrier density distribution over the width of the stripe.

The main characteristics of room-temperature light-emitting diodes (λ=4.3 μm) based on InAsSbP/InAsSb/InAsSbP III–V semiconductor heterostructures with a variable-gap buffer layer are reported. An optical power P=0.85 mW was achieved with a pulse length of ∼5 μs and 1 kHz repetition frequency. Conditions for maximizing the power of the light-emitting diodes are indicated. An example is given of the use of these diodes to detect carbon dioxide using the 4.3 μm fundamental absorption band.

An investigation was made of continuous tuning of the emission wavelength in two types of InAsSb/InAsSbP diode heterolasers: three-layer structures with combined electrical and optical confinement and five-layer structures with separate confinement. In three-layer structures the emission wavelength initially decreases by 2–4 A with increasing current and then increases by 10–15 A. In five-layer structures the emission wavelength mainly decreases. This difference is attributed to the better flow of carriers in the bulk of the active region in five-layer structures as compared with three-layer ones.

New potentials are demonstrated for the application of scanning electron microscope methods to identifying heteroboundaries, monitoring the sharpness of interfaces, and determining the positions of p-n junctions in laser structures based on InAsSb/InAsSbP, including at low temperatures. The method permits optimization of the parameters of long-wavelength lasers and to obtain record low threshold currents (Ith≤25 mA at T=77 K) for lasing wavelengths λ=3–3.5 μm.

The growth rate evolution versus V/III ratio and substrate temperature was studied by means of optical reflectivity during MBE of GaN layers using NH3 as nitrogen source. The GaN desorption becomes observable at temperatures above 800°C and causes the reduction of growth rate accompanied with the surface roughening at temperatures above 850-870°C. Unlike GaAs, which evaporates in accordance with the action mass law, the desorption rate of GaN is found to be almost independent of V/III ratio within the N-rich growth conditions. The activation energy for GaN desorption during the growth is found to be (3.2±0.1)eV. This value is very close to the activation energy for free evaporation. At V/III ratio values exceeding 200 the GaN growth rate reduction caused by violation of the molecular flow regime is observed. The Mg-doped samples grown under these extreme conditions tend to have improved acceptor activation and thus p-type conductivity.