ТЕНДЕНЦИИ РАЗВИТИЯ ЭПИТАКСИАЛЬНОЙ ТЕХНОЛОГИИ НИТРИДНЫХ СОЕДИНЕНИЙ

The main trends in the development of technology for nitride heterostructures element base of microwave−technology and power electronics, as well as light−emitting diodes have been reviewed. It has been noted that most modern technological focus is the development of nitride heterostructures on silicon substrates. The basic problems of nitride compounds on silicon substrate and the ways of their solution have been discussed. Some results of GaN/Si heterostructures technology development in «Elma−Malachit» JSC have been presented. The AlGaN/GaN/Si heterostructures have been grown by MOCVD. We show that early process stages such as Si−surface treatment and Al pre−deposition are of great importance for the growth of crack−free structures with good structural and surface quality. Meanwhile the surface curvature of the grown structures is influenced mainly by the composition of multilayered transition region between the AlN nucleation layer and the GaN layer. Transistors fabricated on AlGaN/GaN structures grown on Si substrates under optimized conditions demonstrated rather good static characteristics: Id,max = 800 mA/mm, Ubr > 120 V, gm = = 170 mS/mm. For the further technology development experimental and technological work should be arranged in close coordination with analytical prediction and calculation of properties of the grown material with mathematical modeling methods. This approach will help enhance the efficiency of technology development and deepen scientific views on the processes responsible for the formation of properties of heterostructures. Рассмотрены основные тенденции в развитии технологии гетероструктур нитридных соединений для элементной базы СВЧ−техники и силовой электроники, а также светоизлучающих диодов. Отмечено, что важнейшим современным технологическим направлением является разработка гетероструктур нитридных соединений на подложках кремния. Рассмотрены основные проблемы гетероэпитаксии нитридных соединений на подложке кремния и пути их решения. Представлены некоторые результаты разработок технологии гетероструктур нитридных соединений на подложках кремния в ЗАО «Элма−Малахит». Гетерострукуры AlGaN/GaN/Si выращены МОС−гидридным методом. Показано, что предэпитаксиальная обработка подложек кремния и начальная стадия процесса выращивания, включающая предварительное покрытие поверхности Si алюминием при подаче в реактор потока ТМА, играют большую роль в формировании гетероструктур, свободных от трещин и с хорошей морфологией. В то же время установлено, что форма поверхности гетероструктур определяется главным образом композицией переходной области между зародышевым слоем AlN и слоем GaN. Транзисторы, изготовленные на основе выращенных гетероструктур AlGaN/GaN/Si, продемонстрировали приемлемые статические характеристики: максимальная плотность тока составила 800 мА/мм, пробивное напряжение — более 120 В, крутизна — 170 мСм/мм. Показано, что для дальнейшего развития гетероструктур нитридных соединений на подложках кремния экспериментально−технологическую работу необходимо организовать в тесном взаимодействии с аналитическим прогнозированием и расчетами свойств выращиваемого материала методами математического моделирования. Такой подход поможет повысить результативность разработок технологии и углубит научные представления в отношении процессов, ответственных за формирование свойств гетероструктур.

Trends in the development of the epitaxial nitride compounds technology

The main trends in the development of technology for nitride heterostructures element base of microwave-technology and power electronics, as well as light-emitting diodes have been reviewed. It has been noted that most modern technological focus is the development of nitride heterostructures on silicon substrates. The basic problems of nitride compounds on silicon substrate and the ways of their solution have been discussed. Some results of GaN/Si heterostructures technology development in “Elma-Malachit” JSC have been presented. The AlGaN/GaN/Si heterostructures have been grown by MOCVD. We show that early process stages such as Si-surface treatment and Al pre-deposition are of great importance for the growth of crack-free structures with good structural and surface quality. Meanwhile the surface curvature of the grown structures is influenced mainly by the composition of the multilayered transition region between the AlN nucleation layer and the GaN layer. Transistors fabricated on AlGaN/GaN structures grown on Si substrates under optimized conditions demonstrated rather good static characteristics: Id,max=800 mA/mm, Ubr>120 V, gm=170 mS/mm. For further technology development experimental and technological work should be arranged in close coordination with analytical prediction and calculation of properties of the grown material with mathematical modeling methods. This approach will help enhance the efficiency of technology development and deepen scientific views on the processes responsible for the formation of properties of heterostructures

Building an Analytical Model of the Gravitational Grain Movement in an Open Screw Channel with Variable Inclination Angles

Existing technical means for loading silos with grain material do not fully meet the needs of production. The issue related to grain injury remains urgent, which predetermines the need to design a gravitational loader of another principle of operation with the appropriate theoretical justification for the movement of grain material in it. This paper has presented and substantiated the model of the gravitational movement of grain in the peripheral open screw channel with two variable angles of inclination. The model is based on the system of forces in the cylindrical coordinate system, acting on the volume of grain flow in the peripheral screw channel. The grain speed at the end of the braking section of the channel should be as low as possible but not less than the initial flow rate at the beginning of the acceleration section. The model takes into consideration this condition and ensures the optimal passage of grain along any part of the channel. The reported model makes it possible to obtain the speed of grain movement at any time, takes into consideration the height of the bunker hole and the dependence between the angles of inclination of the spirals of acceleration and brake sections. A mathematical dependence is given for these angles that ensures the passage of grain without its discharge and, at the same time, prevents injury to the grain mass due to a controlled decrease in the resulting speed. A separate dependence is provided to find the time at which the grain increases its speed on the acceleration section, reaching the maximum value. Based on the model, a peripheral open screw channel with two angles of inclination of spirals α and β has been proposed. For this channel, the relationships between its key parameters have been established, in particular, values have been substantiated for the recommended angles of 41°…45° for the acceleration section and 39°…35° for the brake section, respectively, as well as the hо/r ratio not less than 0.6...0.7