ENGINEERING TECHNOLOGY

Measured semiconductor boron arsenide, theoretical prediction “stabilized”


On July 22, liu Xinfeng research team, a researcher at the National Nanoscience Center (hereinafter referred to as the Nanoscience Center), published a paper in Science, and for the first time detected its electron hole reduction mobility of about 1550 cm2/Vs in semiconductor boron arsenide, which is very close to the theoretical prediction of 1680 cm2/Vs, which is expected to provide important basic data guidance for the application of semiconductor boron arsenide in the field of integrated circuits.

Schematic diagram of carrier mobility of boron arsenide tested by transient reflection microscopy (Courtesy of the research team)

Excellent material One vote veto?

Mobile phones, computers and other electronic products will be hot after a long time, which is a familiar experience for many people. With the continuous increase in the scale of chip integration, the problem of heat dissipation has become a big problem. Scientists attribute the reason for this phenomenon to the thermal conductivity of silicon 150W/mK, the semiconductor material used to make chips, which is not high enough, and the higher the thermal conductivity, the faster the heat dissipation.

To this end, materials scientists have been looking forward to finding a material with higher thermal conductivity. However, unfortunately, if the thermal conductivity of copper is 400W/mK as a standard, semiconductor materials with higher thermal conductivity are only a few graphene oxides, silicon carbide and so on. “Graphene oxide is difficult to apply due to the limitations of its layered structure. Silicon carbide is a three-dimensional semiconductor that is now widely used, but the thermal conductivity is only 500W/mK. Liu Xinfeng told China Science Daily.

In 2018, three papers were published in Science reporting that American scientists had successfully prepared boron arsenide using chemical vapor deposition methods. In fact, this compound proposed as early as 1958 has not been able to enter the field of people seeking excellent semiconductor materials due to the low thermal conductivity predicted by theory.

Until 2013, with the significant improvement of computer computing power, the properties of a batch of materials were re-predicted. Some scientists predict that the thermal conductivity of boron arsenide can be comparable to the 2000W/mK of diamond, which has aroused great interest in the academic community and the industry.

Not only that, but theoretical predictions also show that boron arsenide also has a very high electron cavity reduction mobility of 1680 cm2/Vs. “This determines the logic speed of the semiconductor material, and the higher the mobility, the faster the operation speed.” Yue Shuai introduced.

This semiconductor material with ultra-high thermal conductivity and mobility is exciting, and future applications in the field of integrated circuits will achieve both thermal difficulties and higher computing speeds.

However, when scientists hold real boron arsenide samples, the measured data is mixed. Happily, the highest measured thermal conductivity of the sample is 1300W/mK, which is close to 10 times that of silicon. Worryingly, a 2021 study showed a mobility rate of only 22 cm2V-1s-1, almost rejecting its possible application in the semiconductor field.

Difficulties, climbing the peaks

For a time, the results of the inconsistency between theoretical prediction and actual measurement made materials scientists a little confused: is the theoretical prediction wrong, or is there a problem with the actual measurement method?

Liu Xinfeng introduced that in this work in 2021, scientists use traditional electrical measurement methods based on the “Hall effect”. “It is necessary to prepare hundreds of micron electrodes on the sample, because there are many impurities in the preparation of the sample at this stage, and there will be errors due to insufficient spatial resolution.” Therefore, the development of a higher spatial resolution method to achieve the measurement of the mobility of boron arsenide samples has become a scientific peak that scientists around the world are scrambling to climb.

For Liu Xinfeng’s research group, this is an ultra-difficult work. First of all, sample preparation is difficult. The Ren Zhifeng research group of the University of Houston is responsible for exploring the experimental conditions and growing samples, while the Liu Xinfeng research group and the Bao Jiming research group of the University of Houston conduct purity characterization. Over the years, they repeated this process countless times, constantly optimizing the experimental conditions.

In Yue Shuai’s memory, making fun in pain is a true portrayal of that period. “The sample contains one-thousandth of a carbon impurity, and once a batch of samples grew, and a test actually measured the signal of the diamond!” Yue Shuai recalled, “Everyone was happy for half a day, but they didn’t expect to accidentally harvest expensive diamonds by growing boron arsenide. ”

Pioneering the frontier and persevering

Once the sample is ready, the next thing you need to do is to select a high-purity sample. In the eyes of researchers, this is a “no man’s land” that no one has ever set foot in before. “The boron arsenide sample has only been prepared for less than 5 years, and its basic physical properties are unclear, and no one knows which area is of high purity.” Liu Xinfeng said.

However, they have been seriously enjoying the role of adventurers who open up knowledge, constantly trying to obtain various characteristics of materials through luminescence, Raman spectroscopy, absorption, thermal conductivity, X-ray diffraction, carrier dynamics, etc., trying to summarize the laws related to purity.

After repeatedly comparing a large number of samples in a long repetitive work, they finally determined a method of combining X-ray, Raman, and banded fluorescence signals to determine the purity of the samples, and selected high-purity samples based on this new method.

Further, the researchers independently built a new set of “ultrafast carrier diffusion microscopic imaging system”. The system is based on optical principles for inspection, avoiding the previous need to use electrodes to cause low spatial resolution defects, and enabling real-time, in situ observation.

Using this measurement system, the researchers systematically compared the diffusion rates of boron arsenide electrons and holes with different impurity concentrations, and for the first time detected a reduction mobility of about 1550 cm2V-1s-1 in the high-purity sample region, which was very close to the theoretical prediction. This undoubtedly gives boron arsenide a “reassuring pill” for the future widely used in optoelectronic devices and electronic components.

Because he once had experience in developing scientific research instruments, and the research group also had an excellent foundation and tradition of building instruments and equipment, from preparation to construction to obtaining perfect data, Yue Shuai only took 2 months, feeling “not difficult”.

However, the process of scientific exploration made Yue Shuai feel that it was not easy. “For basic research, to do something really useful, the results may be slower, but it is worth sticking to it!” He said, “Teacher Liu has also been encouraging and supporting us to do so, to pass on our words and teach by example.”

Yue Shuai, an associate researcher at the Nano Center, is the first author, and Dr. Tian Fei of the University of Houston (now a professor at Sun Yat-sen University) is the co-first author. Liu Xinfeng, a researcher at the Nano Center, is the corresponding author, and Professors Bao Jiming and Ren Zhifeng of the University of Houston are co-corresponding authors. (Source: China Science Daily Gan Xiao )

Related paper information:https://doi.org/10.1126/science.abn4727



Source link

Related Articles

Leave a Reply

Your email address will not be published. Required fields are marked *

Back to top button