Large Signal Performance of the Gallium Nitride Heterostructure Field-Effect Transistor With a Graphene Heat-Removal System

The self-heating effect exerts a considerable influence on the characteristics of high-power electronic and optoelectronic devices based on gallium nitride. An extremely non-uniform distribution of the dissipated power and a rise in the average temperature in the gallium nitride heterostructure field-effect transistor lead to the formation of a hot spot near the conductive channel and result in the degradation of the drain current, power gain and device reliability. The purpose of this work is to design a gallium nitride heterostructure field-effect transistor with an effective graphene heat-removal system and to study using numerical simulation the thermal phenomena specific to it. The object of the research is the device structure formed on sapphire with a grapheme heat-spreading element placed on its top surface and a trench in the passivation layer filled with diamond grown by chemical vapor deposition. The subject of the research is the large signal performance quantities. The simulation results confirm the effectiveness of the heat-removal system integrated into the heterostructure field-effect transistor and leading to the suppression of the self-heating effect and to the improvement of the device performance. The advantage of our concept is that the heat-spreading element is structurally connected with a heat sink and is designed to remove the heat immediately from the maximum temperature area through the trench in which a high thermal conductivity material is deposited. The results of this work can be used by the electronics industry of the Republic of Belarus for developing the hardware components of gallium nitride power electronics.The self-heating effect exerts a considerable influence on the characteristics of high-power electronic and optoelectronic devices based on gallium nitride. An extremely non-uniform distribution of the dissipated power and a rise in the average temperature in the gallium nitride heterostructure field-effect transistor lead to the formation of a hot spot near the conductive channel and result in the degradation of the drain current, power gain and device reliability. The purpose of this work is to design a gallium nitride heterostructure field-effect transistor with an effective graphene heat-removal system and to study using numerical simulation the thermal phenomena specific to it. The object of the research is the device structure formed on sapphire with a grapheme heat-spreading element placed on its top surface and a trench in the passivation layer filled with diamond grown by chemical vapor deposition. The subject of the research is the large signal performance quantities. The simulation results confirm the effectiveness of the heat-removal system integrated into the heterostructure field-effect transistor and leading to the suppression of the self-heating effect and to the improvement of the device performance. The advantage of our concept is that the heat-spreading element is structurally connected with a heat sink and is designed to remove the heat immediately from the maximum temperature area through the trench in which a high thermal conductivity material is deposited. The results of this work can be used by the electronics industry of the Republic of Belarus for developing the hardware components of gallium nitride power electronics

Эксплуатационные характеристики транзистора с высокой подвижностью электронов на основе нитрида галлия с теплоотводящими элементами на основе нитрида бора

A local thermal management solution for high electron mobility transistors based on GaN was developed using a BN layer as a heat-spreading element. The thermally conducting and electrically insulating nature of BN allows it to be placed close to the active area and to be in direct contact with the electrodes and the heat sink, thus introducing an additional heat-escaping route. The numerical simulations of a GaN high electron mobility transistor with the BN heat-spreading element revealed the improvement in the DC, breakdown, small-signal AC and transient characteristics. In case of sapphire substrate, the maximum temperature in the device structure operating at a power density of 3.3 W/mm was reduced by 82.4 °C, while the breakdown voltage at a gate-source voltage of 2 V was increased by 357 V. The cut-off frequency and the maximum oscillation frequency at a gate-source voltage of 6 V and a drain-source voltage of 30 V were enhanced by 1.38 and 1.49 times, respectively. We suppose that the proposed thermal management method can be adapted to other high-power devices.Предлагается метод уменьшения влияния эффекта саморазогрева в транзисторах с высокой подвижностью электронов на основе нитрида галлия, который заключается в использовании слоя нитрида бора в качестве теплоотводящего элемента. Высокая теплопроводность и низкая электрическая проводимость нитрида бора позволяют располагать слой на его основе вблизи активной области и находиться в плотном контакте с электродами и теплопоглощающим элементом, формируя таким образом дополнительный канал для отведения избыточного тепла. Результаты численного моделирования транзистора с высокой подвижностью электронов на основе нитрида галлия с теплоотводящим элементом на основе нитрида бора указывают на улучшение электрических, частотных и переходных характеристик, увеличение напряжения пробоя. В случае сапфировой подложки максимальная температура в структуре прибора, работающего на уровне 3,3 Вт/мм, снижается на 82,4 °С, при этом напряжение пробоя, рассчитанное при напряжении затвор-исток 2 В, повышается на 357 В. Граничная частота и максимальная частота генерации, определенные при напряжении затвор-исток 6 В и напряжении сток-исток 30 В, увеличиваются в 1,38 и 1,49 раз, соответственно. Предлагаемое конструктивно-технологическое решение может использоваться и для других мощных приборов

Leakage current in AlGaN Schottky diode in terms of the phonon-assisted tunneling model

The leakage current in the AlGaN Schottky diode under a reverse bias is simulated and compared within the frameworks of the thermionic emission–diffusion and phonon-assisted tunneling models. It is shown that the phonon-assisted tunneling model is suitable to describe the reverse-bias characteristic of the AlGaN Schottky contact and can also be applied to calculate the gate leakage current in the AlGaN/GaN high electron mobility transistor

Mobility of a two-dimensional electron gas in the AlGaAs/GaAs heterostructure: simulation and analysis

At temperatures above 100 K, a two-dimensional electron gas generated at the AlGaAs/GaAs heterointerface can be characterized by the three dominant scattering mechanisms: acoustic deformation potential, polar acoustic phonon and polar optical phonon. An analytical model describing the two-dimensional electron gas mobility controlled by these scattering processes as a function of the electron concentration and the temperature was developed and integrated into a device simulator package using a built-in C language interpreter. The electrical characteristics of a simple AlGaAs/GaAs high electron mobility transistor were simulated using either the derived or a conventional bulk mobility model and the results were compared

Mobility of a two-dimensional electron gas in the AlGaN/GaN heterostructure: simulation and analysis

At temperatures higher than the room temperature, a two-dimensional electron gas (2DEG) formed at the AlGaN/GaN heterointerface can be characterized by the three dominant scattering mechanisms: acoustic deformation potential, polar acoustic phonon and polar optical phonon scatterings. An analytical model describing the 2DEG mobility limited by these scattering mechanisms as a function of the carrier concentration and the temperature was developed and integrated into a device simulator package using a C language interpreter. The model should be useful for heterostructure device simulators such as Blaze

Magnetic properties of low-dimensional MAX3 (M=Cr, A=Ge, Si and X=S, Se, Te) systems

The article presents the results of a magnetism study in quasi-two-dimensional MAX3 (M=Cr, A=Ge, Si and X=S, Se, Te) systems. We calculated the microscopic magnetic parameters using quantum mechanical methods and showed that MAX3 can have a high spin polarization. The easy magnetization axis lies normal to the layer plane. The main magnetic order of the CrGeSe3, CrGeTe3, CrSiSe3, and CrSiTe3 atomic systems is ferromagnetism. CrGeS3 and CrSiS3 exhibit antiferromagnetism. The low energy stability of the magnetic order is confirmed by the calculated values of the exchange interaction integral (J). We showed that the magnetic order realizes only at low temperatures. A study of the dependences of J and the magnetic anisotropy energy on the structural (distance between magnetic ions, distortion of the octahedral complex) and electronic properties (population and hybridization of atomic and molecular orbitals) has been performed. The dependences indicate three possible mechanisms of the exchange interaction. We have given ways of influencing a specific mechanism for managing exchange interaction

Теплопроводность нитрида галлия с кристаллической структурой типа вюрцита

This paper reviews the theoretical and experimental works concerning one of the most important parameters of wurtzite gallium nitride – thermal conductivity. Since the heat in gallium nitride is transported almost exclusively by phonons, its thermal conductivity has a temperature behavior typical of most nonmetallic crystals: the thermal conductivity increases proportionally to the third power of temperature at lower temperatures, reaches its maximum at approximately 1/20 of the Debye temperature and decreases proportionally to temperature at higher temperatures. It is shown that the thermal conductivity of gallium nitride (depending on fabrication process, crystallographic direction, concentration of impurity and other defects, isotopical purity) varies significantly, emphasizing the importance of determining this parameter for the samples that closely resemble those being used in specific applications. For isotopically pure undoped wurtzite gallium nitride, the thermal conductivity at room temperature has been estimated as high as 5.4 W/(cm·K). The maximum room temperature value measured for bulkshaped samples of single crystal gallium nitride has been 2.79 W/(cm·K)

Physic-topological (electrical) model of a junction field effect transistor, taking into account the degradation of operational characteristics under the influence of penetrating radiation

The results of applying the compact model of junction field effect transistors developed and integrated into the Cadence software product for control to evaluate the hardness of a two-stage differential amplifier circuit under the combined or separate exposure to fluences of electrons, protons and neutrons are presented

First-principles study of anisotropic thermal conductivity of GaN, AlN, and Al0.5Ga0.5N

The thermal stability of devices based on GaN, AlN, and Al0.5Ga0.5N semiconductors is a critical property for efficient and reliable operation. The thermal conductivity of these materials has anisotropic nature. We proposed an approach for calculating the anisotropic thermal conductivity based on harmonic and anharmonic interatomic force constants of a lattice. The thermal-conductivity coefficient of GaN, AlN, and Al0.5Ga0.5N in the [100], [001], and [111] directions were calculated using ab initio methods by solving the linearized Boltzmann transport equation. It equals λ[100] = 259.28, λ[001] = 335.96 and λ[111] = 309.56 W/(m·K) for GaN; λ[100] = 396.06 , λ[001] = 461.65 and λ[111] = 435.05 W/(m·K) for AlN; and λ[100] = 186.74, λ[001] = 165.24 and λ[111] = 177.62 W/(m·K) for Al0.5Ga0.5N at 300 K. The dependence of the coefficient λ(T) on temperature in the range from 250 to 750 K is presented. A comparative analysis of the GaN thermal conductivity investigations has been carried out for experimental studies and theoretical calculations

Теплопроводность нитрида галлия с кристаллической структурой типа вюрцита

This paper reviews the theoretical and experimental works concerning one of the most important parameters of wurtzite gallium nitride – thermal conductivity. Since the heat in gallium nitride is transported almost exclusively by phonons, its thermal conductivity has a temperature behavior typical of most nonmetallic crystals: the thermal conductivity increases proportionally to the third power of temperature at lower temperatures, reaches its maximum at approximately 1/20 of the Debye temperature and decreases proportionally to temperature at higher temperatures. It is shown that the thermal conductivity of gallium nitride (depending on fabrication process, crystallographic direction, concentration of impurity and other defects, isotopical purity) varies significantly, emphasizing the importance of determining this parameter for the samples that closely resemble those being used in specific applications. For isotopically pure undoped wurtzite gallium nitride, the thermal conductivity at room temperature has been estimated as high as 5.4 W/(cm·K). The maximum room temperature value measured for bulkshaped samples of single crystal gallium nitride has been 2.79 W/(cm·K).Выполнен анализ теоретических и экспериментальных исследований одного из важнейших параметров нитрида галлия с кристаллической структурой типа вюрцита – теплопроводности. Так как перенос тепла в нитриде галлия осуществляется главным образом с помощью фононов, его теплопроводность имеет температурную зависимость, характерную для большинства неметаллических кристаллов: увеличивается пропорционально третьей степени температуры в области низких температур, достигает своего максимального значения при температуре, приблизительно равной 1/20 от дебаевской, и уменьшается пропорционально температуре в области высоких температур. Показано, что в зависимости от условий (технология изготовления образца, кристаллографическое направление, концентрация примеси и других дефектов, изотопный состав) теплопроводность нитрида галлия может находиться в большом диапазоне значений, что указывает на важность определения этого параметра именно тех образцов материала, которые используются в конкретных приложениях. Теплопроводность нелегированного изотопно-чистого нитрида галлия при комнатной температуре оценивается на уровне 5,4 Вт/(см·К). Максимальная теплопроводность, достигнутая для объемного образца из монокристаллического нитрида галлия, равна 2,79 Вт/(см·К)