Russian scientists radically improved semiconductors for radars

A.V. Institute of Semiconductor Physics Rzhanova SB RAS

The main component of microwave devices are transistors with high electron mobility, which are created using gallium nitride (GaN), which reduces the number of transistors in cascades of microwave devices, increase their power and ensure stability at elevated temperatures, the presence of radiation background. But the problem in the synthesis process is oxygen, which can be embedded in the crystal structure of the semiconductor material GaN, changing the electrophysical properties. Including leading to the fact that gallium nitride begins to conduct current, where it should act as a dielectric.

“We were able to get rid of parasitic conductivity in the buffer layer of gallium nitride by choosing certain parameters of the growth conditions. Gallium nitride transistors are created on the basis of semiconductor heterostructures containing several layers. One of them - buffer - must have high resistance. It is in this layer that a two-dimensional electron gas is located - a conducting element of the transistor. However, due to oxygen atoms introducing charge carriers - electrons, leakage currents appear in the buffer layer. The latter leads to the degradation of the electrophysical characteristics of the transistor and, as a consequence, to a decrease in the power of the transistor, ”said the leading engineer-technologist at the Laboratory of Molecular Beam Epitaxy (MBE) of A3B5 semiconductor compounds of the Institute of Semiconductor Physics named after A.V. Rzhanova SB RAS Timur Malin.

Instead of additionally introducing carbon or iron to capture “extra” electrons or deliberately creating defects in the initial GaN layers, scientists at the IPP SB RAS found another way to avoid problems in the synthesis of semiconductor material. The solution to the situations was the mechanism of manipulation of growth conditions, which allowed us not to add any impurities and maintain the structural perfection of the gallium nitride layer.

“Using a specific mathematical algorithm, we calculated the optimal growth parameters for creating a buffer layer with high electrical resistance. As a result, when growing semiconductor heterostructures, we used lower temperatures (800 degrees from the range of 800–920 degrees Celsius) at an ammonia flow rate of 250 milliliters per minute. This made it possible to reduce the entry of oxygen into the buffer layer of gallium nitride. We also made sure that the selected parameters do not lead to a deterioration of other properties of the entire multilayer semiconductor structure, ”said Malin.

The next step of the scientists will be testing the technological process on a more modern automated and productive installation for the synthesis of nitride heterostructures “Compact 21-N” of the French company Riber, which will make it possible to make larger semiconductor heterostructures in less time for Russian manufacturers of power and microwave electronics.

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