Translation. Region: Russian Federation –
Source: Novosibirsk State University –
An important disclaimer is at the bottom of this article.
Gaysaa Hamud, a postgraduate student at NSU and a research assistant at the Laboratory of Functional Diagnostics of Low-Dimensional Structures for Nanoelectronics at the Analytical and Technological Research Center "High Technologies and Nanostructured Materials" of the NSU Faculty of Physics, was awarded a diploma for the best oral presentation, "Study of the Conductivity Type of Films of Non-Silicate Germano-Silicate Glasses," at the 16th Valiev International Conference "Micro- and Nanoelectronics – 2025," held from October 6 to 10 in Yaroslavl. The young researcher, who is also a research engineer at the A.V. Rzhanov Institute of Semiconductor Physics of the Siberian Branch of the Russian Academy of Sciences, presented her paper in the "Materials for Optoelectronic Devices" section. For Gaysaa Hamoud, this presentation was her first oral presentation at an adult conference; previously, she had successfully participated only in student and youth conferences.
“We were the first to study the type of conductivity in germanosilicate glasses. This is the novelty of my research. This knowledge is important for understanding the conductivity mechanism in these nonideal dielectrics (in which so-called leakage currents are significant). In any materials – both semiconductors and dielectrics – there is a different type of conductivity: either electronic type, or hole, or bipolar. To improve the performance of devices that use a particular dielectric, it is important to know what type of conductivity is characteristic of it. The object of study in my research was germanosilicate glasses, which can be used for the manufacture of photosensitive MIS structures (metal-insulator-semiconductor structures). Previously, we obtained in them the effect of very good photosensitivity, which is important in their application for technical vision, light-sensitive sensors and memristors, and decided to explain the mechanism of its occurrence. The fact is that germanosilicate glasses are not an ideal dielectric; they conduct electric current. We take advantage of the non-ideal nature of germanosilicate glass (leakage currents) to achieve the beneficial properties of MIS structures based on them. For example, in MIS structures such dielectrics suppress the dark current, but do not greatly weaken the photocurrent. This leads to an improvement in their photosensitivity. And, perhaps, devices based on such dielectrics will replace more expensive industrial photosensitive devices. It is possible that such new materials and devices will be inexpensive, small in size, and consume little energy. However, in order to improve photosensitivity, it is necessary to establish the mechanism of photocurrent generation and the type of conductivity, said Gaisaa Hamoud.
The young researcher began studying the properties of germanosilicate glasses at the very beginning of her graduate studies about three years ago, under the supervision of Vladimir Volodin, a leading researcher at the Laboratory of Functional Diagnostics of Low-Dimensional Structures for Nanoelectronics, Department of the Analytical and Thermal Analysis Center, Faculty of Physics, NSU, a leading researcher at the A.V. Rzhanov Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Sciences, a professor in the Department of General Physics, and Doctor of Physical and Mathematical Sciences. It took about a year to study the conductivity type in these structures.
Routine semiconductor methods such as the Hall effect, thermal probes, or dielectric charge relaxation are not applicable in this case for a number of reasons. Therefore, the scientists used the classical nonequilibrium depletion method by injecting minority charge carriers from the substrate into the dielectric in a metal-insulator semiconductor (MIS) structure. This method studies the current-voltage (I-V) and capacitance-voltage (C-V) characteristics of samples in the dark and under illumination. The study covered four sample compositions grown on different silicon substrates—n-type with n-type conductivity and p-type with p-type conductivity. A total of eight samples were examined. The authors varied the ratio of germanium oxide to silicon oxide in the films. They noted that silicon oxide has been well studied to date, while germanium oxide remains poorly understood, and a mixture of the two has not been studied at all.
Using the nonequilibrium depletion method with minority carrier injection, we can inject carriers of different charges—both negative and positive—into a dielectric. These are either electrons or holes. We can then observe whether they pass through our dielectric. The essence of this method lies in the controllability of the injection process. It is considered a classic, and researchers have been using it for over 40 years. One of the method's authors is Professor Vladimir Alekseevich Gritsenko of the Institute of Semiconductor Physics SB RAS. Using this method, we discovered that germanosilicate glasses have bipolar conductivity, which can involve both electrons and holes. We then refined this method by analyzing photo-EMF (the electromotive force that occurs in semiconductors when exposed to light). We noticed that no EMF occurs in a dark MIS structure without applying an external voltage. However, when exposed to light, electron-hole pairs are generated in the silicon substrate, which are then separated by the built-in field, generating a photo-EMF. Solar cells operate on the same principle: we expose p-n junction silicon to light, and electron-hole pairs are generated in the sample, which are separated by the field built into the p-n junction. If we short-circuit a light-illuminated MIS structure to a payload, the light energy is converted into electrical energy, explained Vladimir Volodin.
The MIS structures studied, based on germanosilicate glass films, can also be used as solar cells, but this was not the goal of the study, so the scientists did not optimize the relevant parameters. For this reason, their efficiency as solar cells does not exceed 0.01%, while 10% is required. Therefore, using them for this purpose is impractical, but that was not the researchers' intended purpose.
MIS structures based on germanosilicate films were studied in the dark and with illumination. Subsequently, by analyzing the nonequilibrium depletion during minority carrier injection from the substrates, the scientists concluded that germanosilicate glass films of various compositions exhibit bipolar conductivity. These findings were confirmed by analyzing the sign of the photo-EMF generated in the MIS structures under illumination.
It was important to confirm the results obtained from studying the current-voltage and capacitance-voltage characteristics. For this, we used an approach based on photo-EMF analysis. In our structures, even without applying an external voltage, but only under the influence of light, we observed depletion with band bending of approximately 0.5 volts in both substrate types. In our opinion, photo-EMF should not occur in the case of purely hole conductivity in an n-type silicon substrate, because holes do not accumulate in them but pass through the dielectric. However, if the resulting voltage reached the flat-band voltage (0.5 volts), this would indicate the presence of only n-type conductivity. However, when photo-EMF occurs that does not reach the flat-band voltage, both n-type and hole conductivity are present. We found that this effect is observed in all our samples when the photo-EMF is lower than the flat-band voltages for n-type and p-type silicon. Simply put, if the photo-EMF is zero, one type of conductivity is present, depending on the substrate; if the photo-EMF reaches its maximum values, another type is present. At intermediate photo-EMF values, both types of conductivity are present simultaneously, said Gaysaa Hamoud.
This fact further confirms that germanosilicate glass exhibits bipolar conductivity. In the future, the scientists intend to focus on improving the photosensitivity of the MIS structures they are studying. The results of this research will be applied in the creation of photodetectors based on MIS structures without a p-n junction. Currently, commercially available photosensitive devices operate using a p-n junction, but photosensitive devices without this junction will be less expensive and easier to manufacture.
Please note: This information is raw content obtained directly from the source. It represents an accurate account of the source's assertions and does not necessarily reflect the position of MIL-OSI or its clients.