D. Yu. Protasov

Bio: D. Yu. Protasov is an academic researcher from Russian Academy of Sciences. The author has contributed to research in topics: Molecular beam epitaxy & Heterojunction. The author has an hindex of 6, co-authored 30 publications receiving 116 citations. Previous affiliations of D. Yu. Protasov include Novosibirsk State Technical University.

The influence of impurity profiles on mobility of two-dimensional electron gas in AlGaAs/InGaAs/GaAs heterostructures modulation-doped by donors and acceptors

Abstract: The low-temperature mobility of two-dimensional electron gas (2DEG) limited scattering by ionized impurities, alloy disorder, acoustic and optical phonons, and interface roughness was calculated for novel pseudomorphic modulation-doped by donors and acceptors InGaAs/AlGaAs quantum well structures promising for high power microwave transistors. Due to the high 2DEG density in the quantum well intersubband transitions were taken into account. Scattering by the ionized donors from δ-layer located in AlGaAs barriers dominates, whereas scattering by the ionized acceptors occupying the most part of AlGaAs barriers is negligibly weak. The width of donor doping profile is a key parameter to control 2DEG mobility, thus, increasing of the profile width from 0.25 nm to 4 nm due to segregation and diffusion of donor atoms halves the mobility. We have proposed a few approaches for the weakening of Coulomb scattering and the increase in 2DEG mobility in the novel heterostructures. The predicted mobility enhancement due to δ-layer splitting into two δ-sublayers was verified experimentally.

Electron scattering in AlGaN/GaN heterostructures with a two-dimensional electron gas

Abstract: The temperature and concentration dependences of electron mobility in AlGaN/GaN hetero-structures are studied. The mobility for the samples under study at T = 300 K lies in the range of 450–1740 cm2/(V s). It is established that scattering at charged centers is dominant for samples with low mobility (lower than 1000 cm2/(V s) right up to room temperature. These centers are associated with a disordered piezoelectric charge at the heterointerface because of its roughness or with a piezoelectric charge similarly to the Al-GaN barrier because of alloy disorder, as well as with the deformation field around dislocations. Scattering at optical phonons is dominant for samples with mobility exceeding 1000 cm2/(V s) at T = 300 K. Scattering at alloy disorders, heterointerface roughness, and dislocations are dominant at temperatures lower than 200 K. A decrease in the influence of scattering at roughness with improvement of the heterointerface morphology increases room-temperature mobility from 1400 cm2/(V s) to 1700 cm2/(V s).

Characterization of MBE‐grown AlGaN layers heavily doped using silane

Abstract: The Alx Ga1–xN layers with a wide range of AlN molar fraction (0 < x < 0.6) were grown by ammonia MBE on (0001)-oriented sapphire substrates using silane as the silicon dopant. The structural, electrical and optical properties of the layers were investigated by atomic force microscopy, X-ray diffraction, Hall, Raman, photoluminescence and cathodoluminescence measurements. It was found that doping affects surface morphology, dislocation density and luminescence intensity of the Alx Ga1–xN layers. A sharp decrease of the luminescence intensity for the heavily doped GaN and Al0.3Ga0.7N layers was explained by enhancement of the nonradiative recombination rate in degenerate GaN layers and by an increase in the defect concentration in AlGaN layers. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Influence of the additional p + doped layers on the properties of AlGaAs/InGaAs/AlGaAs heterostructures for high power SHF transistors

Abstract: The peculiarities of a new type of pseudomorphic AlGaAs/InGaAs/AlGaAs heterostructures with the additional acceptor doping of barriers used for the creation of the power SHF pseudomorphic high electron mobility transistor (pHEMT) have been studied. A comparison of the transport characteristic of the new and typical pHEMT heterostructures was carried out. The influence of the doped acceptor impurities in the AlGaAs barriers of the new pHEMT heterostructure on the transport properties was studied. It was shown that the application of the additional p+ doped barrier layers allows the achievement of a double multiplex increase in the two-dimensional electron gas (2DEG) concentration in the InGaAs quantum well with no parasite parallel conductivity in the AlGaAs barrier layers. An estimation of the concentration of the doped donors and acceptors penetrating into the deliberately undoped InGaAs quantum well from the AlGaAs barriers was performed by second ion mass spectrometry and photoluminescence spectrometry methods. Taking into account the electron scattering by the ionized impurity atoms, calculation of the electron mobility in the InGaAs channel showed that some reduction of the electron mobility results from scattering by the ionized Si donor due to an increase in the Si concentration and, therefore, is not caused by the application of additional p+ doped layers in the construction of pHEMT heterostructures.

Growth of AlGaN/GaN heterostructures with a two-dimensional electron gas on AlN/Al 2 O 3 substrates

Abstract: The possibility of using AlN/Al2O3 substrates to grow AlGaN/GaN hetero-epitaxial structures with a two-dimensional electron gas is studied. A method of calibrating the temperature of the substrates by measuring the thermal radiation spectrum is proposed. Differences between AlN/Al2O3 substrates that lead to differences in the electrophysical parameters of the grown structures are determined. AlN/Al2O3 substrates were used to grow AlGaN/GaN samples with a two-dimensional electron gas mobility in excess of 1300 cm2/(V · s) at an electron concentration in the channel higher than 1013 cm−2.

A Highly Responsive Self-Driven UV Photodetector Using GaN Nanoflowers

Abstract: The rising demand for optoelectronic devices to be operable in adverse environments necessitates the sensing of ultraviolet (UV) radiation. Here, a self-driven, highly sensitive, fast responding GaN nanoflower based UV photodetector is reported. By developing unique structures, the light absorption increases efficiently and a maximum responsivity of 10.5 A W-1 is achieved at 1 V bias. The reported responsivity is the highest among the GaN UV photodetectors on Si substrates and commercially available Si-based UV photodetectors. Under self-driven condition, the photodetector exhibits very low dark current (approximate to nA) with a very high responsivity (132 mA W-1) and detectivity (2.4 x 10(10) Jones). A remarkably high light-to-dark current ratio of approximate to 260 signifies extremely high photodetection gain compared to planar GaN-based photodetectors. The self-driven and biased photodetector device yields highly stable rise and decay time response. A model based on band theory elucidates the origin of self-driven photodetectors. Implementation of the innovative growth design structures assures an exceptionally high sensitivity toward UV signal, which is capable of substituting the existing technology of UV photo-detectors. High responsivity and detectivity from devices based on the GaN nanoflower-like structure with the advantage of high surface/volume ratio can have numerous applications in fabrication of nanoscale optoelectronic high performance devices such as self-driven UV photodetectors.

Electrical characterization of n-type Al0.30Ga0.70N Schottky diodes

Abstract: The carrier trapping properties and current transport behavior of Ni/n-Al0.30Ga0.70N Schottky diodes were quantitatively characterized by a combination of deep level optical spectroscopy (DLOS), thermally based deep level transient spectroscopy (DLTS), current-voltage-temperature (I-V-T), and internal photoemission (IPE) measurements. High quality Schottky diode behavior was observed with an IPE-determined barrier height of 1.66 eV and the observed temperature-independent reverse leakage current behavior was found to be consistent with field emission in reverse bias and thermionic-field emission in forward bias as the dominant transport mechanisms. The trap spectroscopy measurements revealed the presence of several bandgap states located at EC–0.9 eV (seen by both DLOS and DLTS), EC–1.5, EC–3.11, and EC–3.93 eV—all via DLOS. The EC–3.10 level, which is present in very high concentration, is found to correlate with the energy position expected for the cation vacancy in AlGaN, based on the vacuum referred binding energy model for the AlxGa1−xN alloy. The relatively shallow trap at EC–3.93/EV+0.15 eV, which is possibly Mg-related, is also present in significant concentration. The total observed trap concentration in this sample is in excess of the net doping extracted from capacitance-voltage, which will likely impact device behavior and is consistent with the observed I-V-T behavior.

Access-Region Defect Spectroscopy of DC-Stressed N-Polar GaN MIS-HEMTs

Abstract: Distinct trap levels in the drain access regions of an N-polar GaN MIS-HEMT are investigated before and after semi-on dc stressing by thermal and optical trap spectroscopies. The most prominent dc stress effect was an increase in concentration of a pre-existing electron trap with an activation energy of 0.54 eV, accompanied by a decrease in concentration of an electron trap with a 0.65-eV activation energy. These distinct states had similar concentrations before stressing, with the 0.54-eV trap concentration dominating (by 6×) after stress. Deeper states revealed via optical measurements showed a mild ~20% increase in total concentration after stressing.

The influence of impurity profiles on mobility of two-dimensional electron gas in AlGaAs/InGaAs/GaAs heterostructures modulation-doped by donors and acceptors

Abstract: The low-temperature mobility of two-dimensional electron gas (2DEG) limited scattering by ionized impurities, alloy disorder, acoustic and optical phonons, and interface roughness was calculated for novel pseudomorphic modulation-doped by donors and acceptors InGaAs/AlGaAs quantum well structures promising for high power microwave transistors. Due to the high 2DEG density in the quantum well intersubband transitions were taken into account. Scattering by the ionized donors from δ-layer located in AlGaAs barriers dominates, whereas scattering by the ionized acceptors occupying the most part of AlGaAs barriers is negligibly weak. The width of donor doping profile is a key parameter to control 2DEG mobility, thus, increasing of the profile width from 0.25 nm to 4 nm due to segregation and diffusion of donor atoms halves the mobility. We have proposed a few approaches for the weakening of Coulomb scattering and the increase in 2DEG mobility in the novel heterostructures. The predicted mobility enhancement due to δ-layer splitting into two δ-sublayers was verified experimentally.

Plasma-Induced Damage and Recovery on Au/n-GaN Schottky Diode in Different Processes

Abstract: The effects of plasma-induced damage on deep traps in n-GaN have been investigated using current–voltage (I–V), capacitance–voltage (C–V), and photocapacitance (PHCAP) measurements. The Au/n-GaN Schottky barrier diodes were fabricated in an inductively coupled plasma ion etching (ICP-RIE) system. After mesa etching to achieve ohmic contact, the n-GaN surface, at which Schottky contacts are fabricated, is etched ~100 nm by ICP-RIE with various Cl2/Ar ratios and RIE bias powers (PB), to introduce plasma damage. The electrical properties of the fabricated Shottky barrier diodes (SBDs) strongly dependent on the RIE gas composition and the bias power PB applied to the sample stage. In order to overcome the residue and plasma damage on the Schottky area, the samples were treated with HCl at 110 °C for 30 min. Several deep levels (1.8, 2.5, and 3.0 eV below the conduction band) were detected by PHCAP measurement. Improved electrical characteristics were achieved as a result of the HCl treatment and sintering process. The PHCAP measurement results also revealed the effectiveness of thermal and chemical treatments.