A. Yu. Pavlov

AlGaN/GaN-HEMTs with a breakdown voltage higher than 100 V and maximum oscillation frequency fmax as high as 100 GHz

The N-Al0.27Ga0.73N/GaN High Electron Mobility Transistors (HEMTs) with different gate lengths Lg (ranging from 170 nm to 0.5 μm) and gate widths Ws (ranging from 100 to 1200 μm) have been studied. The S parameters have been measured; these parameters have been used to determine the current-gain cutoff frequency ft, the maximum oscillation frequency fmax, and the power gain MSG/MAG and Mason’s coefficients were investigated in the frequency range from 10 MHz to 67 GHz in relation to the gate length and gate width. It was found that the frequencies ft and fmax attain their maximum values of ft = 48 GHz and fmax = 100 GHz at Lg = 170 nm and Wg = 100 μm. The optimum values of Wg and output power P out of the basic transistors have been determined for different frequencies of operation. It has also been demonstrated that the 170 nm Al0.27Ga0.73N/GaN HEMT technology provides both good frequency characteristics and high breakdown voltages and is very promising for high-frequency applications (up to 40 GHz).

Fabrication of a terahertz quantum-cascade laser with a double metal waveguide based on multilayer GaAs/AlGaAs heterostructures

The Postgrowth processing of GaAs/AlGaAs multilayer heterostructures for terahertz quantumcascade lasers (QCLs) are studied. This procedure includes the thermocompression bonding of In–Au multilayer heterostructures with a doped n+-GaAs substrate, mechanical grinding, and selective wet etching of the substrate, and dry etching of QCL ridge mesastripes through a Ti/Au metallization mask 50 and 100 μm wide. Reactive-ion-etching modes with an inductively coupled plasma source in a BCl3/Ar gas mixture are selected to obtain vertical walls of the QCL ridge mesastripes with minimum Ti/Au mask sputtering.

Investigation of the fabrication processes of AlGaN/AlN/GaN НЕМТs with in situ Si3N4 passivation

The optimum mode of the in situ plasma-chemical etching of a Si3N4 passivating layer in C3F8/O2 medium is chosen for the case of fabricating AlGaN/AlN/GaN НЕМТs. It is found that a bias of 40–50 V at a high-frequency electrode provides anisotropic etching of the insulator through a resist mask and introduces no appreciable radiation-induced defects upon overetching of the insulator films in the region of gate-metallization formation. To estimate the effect of in situ Si3N4 growth together with the heterostructure in one process on the AlGaN/AlN/GaN НЕМТ characteristics, transistors with gates without the insulator and with gates through Si3N4 slits are fabricated. The highest drain current of the AlGaN/AlN/GaN НЕМТ at 0 V at the gate is shown to be 1.5 times higher in the presence of Si3N4 than without it.

Designing gallium nitride-based monolithic microwave integrated circuits for the Ka, V, and W bands

A technology for fabricating multifunction monolithic microwave integrated circuits (MMICs) based on gallium nitride (GaN) heterostructures, which operate at the frequency range up to 100 GHz (the Ka, V, and W bands), is developed. Power amplifier (PA) MMICs operating at 90 GHz are fabricated using the coplanar technology with the gain coefficient being up to 15 dB and the specific output power exceeding 500 mW/mm. In addition, microstrip technology with the use of the polymer dielectric and grounding metallization over the wafer surface without through holes in the substrate is approved. The parameters of the MMICs for multifunction single-chip transmit-receive modules (TRMs), as well as the parameters of the MMICs for intermediate-frequency amplifiers (IFAs), voltage-controlled oscillators (VCOs), low noise amplifiers (LNAs), PAs, and balanced mixers operating in the Ka and V bands (up to 70 GHz), which are fabricated using the proposed technology, are presented.

Terahertz radiation generation in multilayer quantum-cascade heterostructures

I–V and radiative characteristics of multilayer quantum-cascade GaAs/AlGaAs heterostructures with a double metal waveguide are investigated. The I–V characteristics typical of the quantum-cascade lasers are seen. The observed threshold-intensity growth and narrow radiation spectrum are characteristic of laser generation. The measured radiation frequency was found to be about 3 THz, which coincides with the calculated value. Thus, fully domestic terahertz quantum-cascade lasers are demonstrated for the first time.

The influence of gate length on the electron injection of velocity in an AlGaN/AlN/GaN НЕМТ channel

Field-effect high-electron-mobility transistors (HEMTs) based on AlGaN/AlN/GaN heterostructures with various gate lengths Lg have been studied. The maximum values of current and power gaincutoff frequencies (fT and fmax, respectively) amounted to 88 and 155 GHz for HEMTs with Lg = 125 nm, while those for the transistors with Lg = 360 nm were 26 and 82 GHz, respectively. Based on the measured S-parameters, the values of elements in small-signal equivalent schemes of AlGaN/AlN/GaN HEMTs were extracted and the dependence of electron-injection velocity vinj on the gate–drain voltage was determined. The influence of Lg and the drain–source voltage on vinj has been studied.

Electrical and thermal properties of photoconductive antennas based on In x Ga1 – x As (x > 0.3) with a metamorphic buffer layer for the generation of terahertz radiation

The results of studies of the electrical and thermal properties of photoconductive antennas for terahertz-radiation generation are reported; these antennas are fabricated on the basis of low-temperaturegrown GaAs (LT-GaAs) and InxGa1 – xAs with an increased content of indium (x > 0.3). It is shown that the power of Joule heating PH due to the effect of “dark” current in InxGa1 – xAs exceeds the same quantity in LT-GaAs by three–five times. This is due to the high intrinsic conductivity of InxGa1 – xAs at x > 0.38. Heatremoval equipment for the photoconductive antenna has been developed and fabricated. The results of numerical simulation show that the use of a heat sink makes it possible to reduce the operating temperature of the antenna based on LT-GaAs by 16%, of the antenna based on In0.38Ga0.62As by 40%, and for antennas based on In0.53Ga0.47As by 64%.

On a two-layer Si3N4/SiO2 dielectric mask for low-resistance ohmic contacts to AlGaN/GaN HEMTs

The fabrication of a two-layer Si3N4/SiO2 dielectric mask and features of its application in the technology of non-fired epitaxially grown ohmic contacts for high-power HEMTs on AlGaN/GaN heterostructures are described. The proposed Si3N4/SiO2 mask allows the selective epitaxial growth of heavily doped ohmic contacts by nitride molecular-beam epitaxy and the fabrication of non-fired ohmic contacts with a resistance of 0.15–0.2 Ω mm and a smooth surface and edge morphology.

The thermal stability of nonalloyed ohmic contacts to AlGaN/GaN heterostructures

Degradation of nonalloyed ohmic contacts with heavily doped GaN epitaxially grown to the heterostructures with two-dimensional electron gas has been investigated. The change in the relative contact resistivity at temperatures of up to 600°C for the Ti/Pd/Au, Cr/Au, and Cr/Pd/Au metallization compositions has been studied. It is demonstrated that the Cr/Pd/Au metallization composition, the resistivity of which decreases at working temperatures of 400°C, is the most resistant to the effect of temperature. It is shown for the first time that the largest contribution to the increase in the contact resistivity to two-dimensional electron gas upon heating above 400°C is made by the resistivity of the Cr/Pd/Au–n+-GaN metal–dielectric structure, while, at temperatures of 400°C and higher, the resistance between heavily doped GaN and two-dimensional electron gas decreases.

Alloyed Si/Al-based ohmic contacts to AlGaN/GaN nitride heterostructures

For the first time in Russia, the Si/Al/Ti/Au alloyed contact composition is investigated for the formation of ohmic contacts to AlGaN/GaN heterostructures using thermal annealing. The obtained results are compared with those for conventional Ti/Al/Ni/Au ohmic contacts. Use of the composition under investigation makes it possible to decrease the annealing temperature to 675–700°C, which results in improvement in the morphology of alloyed ohmic contacts in comparison with conventional contacts. The value of the contact resistance using the Si/Al-based composition to the AlGaN/GaN heterostructure is obtained in relation to the temperature and annealing duration. It is shown that no qualitative change in the resistance occurs at an annealing duration of several minutes in the temperature range of 700–750°C. In the temperature range of 675–700°C, there is an asymptotic decrease in the contact resistance with increasing annealing duration. The smallest value of the contact resistance amounts to 0.41 Ω mm.