The first results of double -channel heterostructures with donor-acceptor doping and systems of alternating thin layers of AlAs/GaAs forming additional digital potential barriers study are presented. It is shown that due to the peculiarities of real space electron transfer in the proposed design, when the surface density of electrons with high mobility is doubled compared to traditional single-channel bilaterally doped heterostructures, even in the absence of digital barriers, the drift velocity overshot does not decrease. The introduction of digital barriers significantly increases the of electrons drift velocity overshot when they fly into the region of a strong field, bringing the drift velocity overshot in the corresponding heterostructures closer to the theoretical limit for the model used – the drift velocity overshot in the undoped bulk material of the channel.

A simple design of a GaN field-effect transistor on a Si substrate with efficient heat removal through polydiamond layers formed on the walls of grounding holes is proposed. According to calculations, as a result of the introduction of such a heat sink with the same average distance between the gate sections, the maximum temperature in the channel of the GaN transistor on the Si substrate decreases significantly and becomes comparable to the maximum temperature in the channel of the GaN transistor on the SiC substrate.. Keywords: GaN FET, ground hole, channel temperature, polydiamond.

A simple design of a GaN field-effect transistor on a Si substrate with efficient heat removal through polydiamond layers formed on the walls of grounding holes is proposed. According to calculations, as a result of the introduction of such a heat sink with the same average distance between the gate sections, the maximum temperature in the channel of the GaN transistor on the Si substrate decreases significantly and becomes comparable to the maximum temperature in the channel of the GaN transistor on the SiC substrate.

The nonlocal dynamics of electrons in pseudomorphic AlGaAs/GaAs/InGaAs heterostructures with double-sided donor-acceptor doping of AlGaAs barriers and additional digital potential barriers of short-period AlAs/GaAs superlattices around the doped regions has been theoretically studied. For the studied heterostructures, the introduction of digital barriers significantly, by 30–40%, increases the electrons drift velocity overshot when they enter the region of a strong field. The effect of localization of hot electrons on the states in AlAs/GaAs superlattices along the edges of the InGaAs quantum well is revealed. It is shown that taking this effect into account significantly increases the electrons drift velocity overshot, bringing it closer to the maximum theoretical limit for the model used – the drift velocity overshot in the undoped InGaAs bulk material.

The pHEMT heterostructures optimized in this work to improve the parameters of switching microwave transistors have a one-sided δ-doping at 6×1012 cm-2 and an AlAs/GaAs spacer. Such heterostructures were used to fabricate the monolithic integrated circuits of single-pole double throw pHEMT switches with gate length and width of 0.5 μm and 100 μm, respectively. The resulting transistors had the following parameters: gm = 400 mS/mm, saturation current ID=380 mA/mm, ON-state resistance 1.0 Ω×mm, OFF-state capacitance 0.37 pF/mm. The switch parameters at 20 GHz are: insertion loss -2.2 dB, isolation -56 dB, return loss -11.7 dB, linearity P1dB 21 dBm and IIP3 40 dBm.

The first results of the electrons drift velocity study in inverted AlGaAs/InGaAs/GaAs pseudomorphic heterostructures with donor-acceptor doping and short-period AlAs/GaAs superlattices are presented. It is theoretically shown that the introduction of superlattices significantly, up to one and a half times, increases the electrons drift velocity overshot when they enter the region of a strong field. Localized states in the superlattice between the quantum well and the substrate have been found. It is shown that this effect leads to an additional increase in the electrons drift velocity overshot up to the theoretical limit for the model used, i.e., a drift velocity overshot in the bulk material of the quantum well.

The processes of nonlocal electron heating in transistor heterostructures based on gallium nitride and gallium arsenide were compared. It has been shown that, in the case of GaAs double doped pseudomorphic heterostructures, the real space transfer of electrons significantly reduces their drift velocity overshot in the region of a strong field as compared with pure bulk GaAs, while in GaN-based heterostructures the decrease in the drift velocity overshot does not exceed 30% in the studied cases. Keywords: Real space transfer, field-effect transistor, gain factor

The nonlocal electrons heating in transistor heterostructures based on gallium nitride and arsenide is compared. It is shown that if, in comparison with a pure bulk material, in the case of GaAs double doped pseudomorphic heterostructures, the real space transfer of electrons significantly reduces their drift velocity overshot in the region of a strong field, then for GaN-based heterostructures, the decrease of the drift velocity overshot in the studied cases does not exceed 30%.

The nonlocal dynamics of electrons in pseudomorphic AlGaAs/GaAs/InGaAs heterostructures with double-sided donor-acceptor doping of AlGaAs barriers and additional digital potential barriers of short-period AlAs/GaAs superlattices around the doped regions has been theoretically studied. For the studied heterostructures, the introduction of digital barriers significantly, by 30-40%, increases the electrons drift velocity overshot when they enter the region of a strong field. The effect of localization of hot electrons on the states in AlAs/GaAs superlattices along the edges of the InGaAs quantum well is revealed. It is shown that taking this effect into account significantly increases the electrons drift velocity overshot, bringing it closer to the maximum theoretical limit for the model used --- the drift velocity overshot in the undoped InGaAs bulk material. Keywords: potential barriers, digital barriers, heterostructures, electrons drift velocity overshot.

Based on the previously developed computer program for rigorous calculation of modes in optical fibers containing layers of various materials of arbitrary, including nanometer, thickness, the calculation and optimization of single-mode double adiabatic tapers covered with one, two and three-layer films: ITO, ITO/TiO 2 , TiO 2 /ITO/TiO 2 of equal thickness is performed, with the aim of their application as the environment refractive index sensors. It is shown that in the range of wavelengths 1.00–1.6 µm, two, and in particular, three-layer coatings not only can increase the sensitivity, but also significantly reduce the width of the lossy mode resonance (LMR), which, in turn, leads to a significant increase in the figure of merit (FOM) of the sensor, defined as the sensitivity/width of the LMR.

We report on the results of investigations of the millimeter-wave field-effect transistors with a 0.14‑μm T-shaped gate with pseudomorphic Al0.3Ga0.7As–In0.22Ga0.78As–Al0.3Ga0.7As heterostructures with additional potential barriers based on a two-sided donor–acceptor channel doping. At a frequency of 40 GHz in a wide gate voltage range, the maximum stable gain of more than 15 dB has been obtained. The maximum oscillation frequency of the device is about 250 GHz, the open-channel specific current density is about 0.7 A/mm, and the gate–drain breakdown voltage is 22–31 V for different versions.

The results of millimeter – wave field – effect transistors with a 0.14 µm T – gate on pseudomorphic heterostructures Al0.3Ga0.7As – In0.22Ga0.78As – Al0.3Ga0.7As with additional potential barriers based on two-way donor-acceptor channel doping study are presented. At a frequency of 40 GHz in a wide range of gate voltages, a maximum stable gain of more than 15 dB is achieved. The maximum frequency of the device generation is about 250 GHz, the specific current density at the open channel is about 0.7 A / mm, the breakdown voltage of the gate-drain, depending on the version, is 22 -31 V.

The results of the rigorous calculation of mode fields in double adiabatic, single-mode etched-out optical fiber tapers coated with thin indium tin oxide films are discussed in the context of their application as environment refractive index sensors. It is shown that at only two particular thicknesses covering the homogeneous section of the taper ITO film about 100 nm and 177 nm, the lossy mode resonance is observed in the wavelength range of 1.50-1.55 µm. Moreover, the sensitivity of a sensor based on a 177 nm coating is significantly higher, and the resonance width is significantly lower than that of a sensor with a 100 nm coating. Optimal from the viewpoint of the figure of merit, values for the diameter of a homogeneous section of the etched fiber are defined.

In this article, we present GaAs millimeter-wave pseudomorphic high-electron-mobility transistor (pHEMT) using sophisticated AlGaAs-InGaAs-GaAs heterostructure with an In 0.22 Ga 0.78 As quantum well located inside an external quantum well formed by space charge regions in AlGaAs layers. In a heterostructure with this design, high mobility [5800 cm 2 /(V · s)] and high density (4.7 × 10 12 cm -2 ) of two-dimensional electron gas at 300 K were obtained. The localization of hot electrons in an external quantum well leads to an increase in their drift velocity and to enhance the dc and RF performances of the device. A field-effect transistor based on such a heterostructure with a T-gate of 0.14 μm in length shows a specific current density of about 0.7 A/mm, transconductance of about 250 mS/mm, gate-drain breakdown voltage in the range 23-31 V, which corresponds to more than 2 W/mm specific output RF power according to a simple estimate. The transistor demonstrates impressive RF characteristics, the maximum stable gain (MSG) of more than 15 dB at 40 GHz and more than 10 dB at 67 GHz, f t = 45 GHz and f max = 250 GHz. The MSG at 40 GHz increases with increasing distance between the gates in the drain and is almost constant in the range 25-55 GHz.

A new type of AlGaAs/InGaAs/GaAs heterostructures with energy barriers formed in the AlGaAs transistor layers adjacent to the InGaAs channel, modulation-doped with donors and acceptors is presented. The height of the barriers associated with the potential of the space charge region in AlGaAs layers reaches 0.8 eV, which makes it possible to double the concentration of electrons in the channel, prevent the transition of hot electrons heated by the electric field into surrounding layers, and increase their saturation drift velocity by around $$1.2{-}1.3$$ times. As a result, microwave power output density of the transistor exceeded the world level by more than 50 $$\%$$ .

A simple phenomenological model for estimating a drift velocity peak in transistor heterostructures with the strong electron localization in the channel is developed using a self-consistent solution of the Schrödinger and Poisson equations and a system of hydrodynamic equations. It is shown that, when an electron enters the region of a strong field, the donor–acceptor doping increases the average drift velocity of electrons several times in the inverted heterostructures and by a factor of 1.5 in the transistor heterostructures based on the double-sided doped In x Ga 1 – x As–Al y Ga 1 – y As and In x Ga 1 – x As–In y Al 1 – y As heterojunctions. In this case, the surface density of electrons in the double-sided doped structures can be more than doubled without a noticeable deterioration of the transport characteristics.

Application of heat-conducting coatings for cooling of high-power FETs based on heterostructures with arsenide–gallium substrate is theoretically analyzed. When the basic technology for manufacturing of transistors is employed in the absence of additional efforts aimed at a decrease in the thermal resistance of the substrate, the application of an additional thermal interface that represents a heat-conducting dielectric coating makes it possible to substantially decrease the overheating of the transistor channel. A several-fold decrease in such overheating can be reached using variations in the thickness of the coating and modification of the transistor structure and working regimes.

Abstract: The theoretical estimation of the effect of electron localization in the upper valleys in the narrow-band channel of transistor heterostructures AlxGa1–xAs-GaAs with two-sided doping on the value оf drift velocity overshoot is carried out. It is shown that for transistor heterostructures with donor-acceptor doping, in which the proportion of electrons transferred from the narrow-band channel to the wide-band material is less than in conventional structures, in some cases, the drift velocity increase can reach 15 % due to the localization of electrons in the upper valleys in the narrow-band channel. The studied effect can be an additional mechanism for increasing the current in transistors based on heterostructures with donor-acceptor doping.

AbstractApplication of heat-conducting coatings for cooling of high-power FETs based on heterostructures with arsenide–gallium substrate is theoretically analyzed. When the basic technology for manufacturing of transistors is employed in the absence of additional efforts aimed at a decrease in the thermal resistance of the substrate, the application of an additional thermal interface that represents a heat-conducting dielectric coating makes it possible to substantially decrease the overheating of the transistor channel. A several-fold decrease in such overheating can be reached using variations in the thickness of the coating and modification of the transistor structure and working regimes.