Silicon is currently the main semiconducting material used in electronic devices. While other semiconducting materials show potential, further research is required for them to become commercially viable. Researchers at King Abdullah University of Science & Technology (KAUST) in Saudi Arabia have now thoroughly analyzed one such material – metal-nitride nanowires – bringing it a step closer to being useful. They report their findings in a paper in Applied Physics Letters.
When metal-nitride semiconductors are arranged into nano-sized wires they become extra sensitive to light, opening possibilities for optical electronics. One notable challenge, however, is that although metal-nitride nanowires perform well at low temperatures, thermal effects can greatly affect their performance at room temperature. To address this problem, Nasir Alfaraj, together with his PhD supervisor Xiaohang Li and colleagues at KAUST, have produced the most detailed study yet of these thermal effects.
The researchers prepared gallium-nitride (GaN)-based nanowires in a p-i-n structure – a sandwich comprising layers of so-called p-type and n-type versions of the semiconductor surrounding an unaltered layer. N-type semiconductors are doped with materials that provide extra electrons, while p-types are doped with materials with fewer electrons, leaving positively-charged ‘holes’ in the crystal structure. Both electrons and holes act as charge carriers, giving semiconductor devices their useful electronic properties.
"We plan to investigate photoinduced entropy in other materials, such as aluminum-gallium-nitride and zinc-oxide nanowires. We will also compare different nanowire diameters and investigate other structures, such as thin films."Nasir Alfaraj, KAUST
"GaN-based p-i-n nanowires are suitable for fabricating signal attenuators, high-frequency digital switches and high-performance photodetectors," said Alfaraj. "Yet, their performance is negatively affected when electrons and holes recombine, especially close to room temperature."
More specifically, when an electric field acts across a nanowire, the balance of electrons and holes can be affected, releasing heat from the device in the form of thermal radiation. The devices effectively act as mini refrigerators, and their performance declines as they cool.
To quantify this effect, Alfaraj and co-workers directed a titanium-sapphire laser onto the nanowires and measured the photoluminescent emissions that came out of the sample. They were then able to calculate the ‘photoinduced entropy’ of the system: a thermodynamic quantity that represents the unavailability of a system's energy for conversion into work due to luminescence refrigeration.
This revealed that at system temperatures above 250K (-23°C), the electron-hole nonradiative recombination processes become dominant – electrons fall into holes, causing a rise in photoinduced entropy and reducing the device performance.
"We plan to investigate photoinduced entropy in other materials, such as aluminum-gallium-nitride and zinc-oxide nanowires," said Alfaraj. "We will also compare different nanowire diameters and investigate other structures, such as thin films." These studies will assist engineers in making metal-nitride nanowire devices that are thermally stable and suitable for everyday use.
This story is adapted from material from KAUST, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.