Linköping University Researchers Uncover Challenges in Thermal ALD of Indium Nitride (InN)

Researchers from the Pedersen Group at Linköping University have investigated the limitations of thermal atomic layer deposition (ALD) for indium nitride (InN). Using quantum-chemical density functional theory calculations, they explored the adsorption process of ammonia (NH3) on InN and compared it to gallium nitride (GaN), shedding light on the challenges in InN deposition.

InN holds promise in semiconductor and electronics applications due to its distinctive properties. It boasts a high electron mobility, exceeding that of many other III-nitride materials, rendering it suitable for high-frequency electronic devices like transistors and amplifiers. With a narrow bandgap of around 0.7 eV, InN finds applications in infrared photodetectors and optoelectronic devices. Despite challenges in thermal stability during deposition, it exhibits good stability when appropriately processed, making it valuable in high-temperature electronics. Its high electron velocity enhances the performance of high-speed field-effect transistors. InN also shows potential in energy-efficient electronics and gas sensing applications, furthering its significance in the semiconductor and electronics industry.

The deposition of indium nitride (InN) using CVD is challenging due to its low thermal stability, which limits the use of high-temperature processes. ALD is an alternative method that can operate at lower temperatures. While ALD has been successful in depositing materials like aluminum nitride and gallium nitride (GaN) using ammonia as a nitrogen precursor in thermal processes, InN can only be deposited using plasma ALD. This suggests a limitation to thermal ALD with ammonia for InN.

Gibbs free energy profile for the adsorption of NH3 onto InN and GaN at 500 (a) and 800 K (b).

Researchers used quantum-chemical density functional theory calculations to investigate the adsorption process of ammonia (NH3) on both GaN and InN surfaces. They aimed to understand if differences in this process could explain why thermal ALD of InN is challenging. Their findings revealed a similar reactive adsorption mechanism on both materials, where NH3 adsorbs onto vacant sites created by the desorption of methyl groups from the surfaces. However, the energy barrier for this adsorption process was significantly higher on InN compared to GaN, indicating that the process is much slower on InN.

This slow kinetics would hinder NH3 from effectively adsorbing onto InN during the ALD growth process, making thermal ALD with InN using NH3 impractical. As a result, the only alternative to a fully thermal ALD process for InN appears to be using a different precursor system due to InN's thermal instability.

Source: On the limitations of thermal atomic layer deposition of InN using ammonia | Journal of Vacuum Science & Technology A | AIP Publishing