The limitations of thermal atomic layer deposition (ALD) for indium nitride (InN) were thoroughly investigated by researchers from the esteemed Pedersen Group at Linköping University. By employing quantum-chemical density functional theory calculations, the team elucidated the intricacies of the adsorption process of ammonia (NH3) on InN and compared it to gallium nitride (GaN), ultimately shedding light on the formidable challenges associated with InN deposition.

A thin layer of indium nitride on silicon carbide, created using the molecule developed by LiU researchers.
The creation of a slim coating of indium nitride on silicon carbide has been achieved through the utilization of the compound developed by researchers from Linköping University (LiU).

InN, with its impressive properties, holds immense promise in the realm of semiconductor and electronics applications. Its outstanding electron mobility, surpassing that of numerous other III-nitride materials, renders it especially well-suited for high-frequency electronic devices such as transistors and amplifiers. Additionally, InN's narrow bandgap of approximately 0.7 eV imparts it with significant utility in infrared photodetectors and optoelectronic devices. Despite the hurdles faced during thermal stability in the deposition process, InN exhibits commendable stability when subjected to appropriate processing conditions, making it particularly valuable to high-temperature electronics. Moreover, its remarkable electron velocity greatly enhances the performance of high-speed field-effect transistors. Furthermore, InN demonstrates potential in energy-efficient electronics and gas sensing applications, further cementing its significance within the semiconductor and electronics industry.

Depositing indium nitride (InN) using the conventional chemical vapor deposition (CVD) technique proves to be a formidable task due to its inherent low thermal stability, which necessitates the avoidance of high-temperature processes. In contrast, ALD, an alternative method capable of operating at lower temperatures, emerges as a promising avenue. While ALD has exhibited noteworthy success in depositing materials such as aluminum nitride and gallium nitride (GaN) utilizing ammonia as a nitrogen precursor in thermal processes, the deposition of InN via thermal ALD remains elusive. Plasma ALD remains the sole viable option for achieving effective InN deposition. This discrepancy strongly suggests a clear limitation to thermal ALD with ammonia for InN.

To discern the underlying cause of this limitation, the research team elected to exploit quantum-chemical density functional theory calculations to dissect the intricate adsorption process of ammonia (NH3) on the surfaces of both GaN and InN. The primary aim was to ascertain whether dissimilarities in this process could account for the challenges encountered in thermal ALD of InN. The findings revealed a strikingly similar reactive adsorption mechanism on both materials, characterized by the adsorption of NH3 onto vacant surface sites formed by the desorption of methyl groups. However, the energy barrier associated with this adsorption process was remarkably higher on InN compared to GaN, unequivocally indicating a significantly slower process occurring on the InN surface.

This sluggish kinetics severely impedes the effective adsorption of NH3 onto InN during the ALD growth process, thereby rendering thermal ALD with InN using NH3 impractical. Consequently, the sole viable alternative to achieving a fully thermal ALD process for InN appears to be the utilization of a distinct precursor system, owing to the intrinsic thermal instability exhibited by InN.

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