InN crystal habit, structural, electrical, and optical properties affected by sapphire substrate nitridation in N-polar InN/InAlN heterostructures. (23rd June 2021)

• Record Type: Journal Article
• Authors: Gucmann, Filip; Kučera, Michal; Hasenöhrl, Stanislav; Eliáš, Peter; Rosová, Alica; Dobročka, Edmund; Stoklas, Roman; Kuzmík, Ján
• Is Part Of: Semiconductor science and technology. Volume 36:Number 7(2021)
• Publication Date: 2021-06-23
• Subjects: MOCVD -- InN -- InAlN -- nitridation -- vicinal substrate -- off-axis substrate; Semiconductors -- Periodicals; 621.38152
• DOI: 10.1088/1361-6641/ac06e4
• Languages: English
• ISSNs: 0268-1242

Abstract

Abstract: Indium nitride (InN) is a very promising direct bandgap semiconductor material for near-infrared optoelectronic devices and high speed transistors, however InN growth is much more challenging compared to other III-N semiconductors. In this study we analysed the impact of pre-growth vicinal c -plane sapphire substrate nitridation on the electrical, optical, and strucutral properties of N-polar InN/InAlN heterostructures and the InN crystal habit. While a short cool-down nitridation phase resulted in a high quality InAlN layer and low quality InN layer, it was the opposite for a long cool-down nitridation phase. A trade-off between the electrical and optical properties was observed: the short nitridation cool-down produced InN layers with a higher electron mobility of 629 cm 2 V −1 s −1 and low photoluminescence (PL) emission, and the long one resulted in InN with a ∼21% lower electron mobility of 497 cm 2 V −1 s −1 but strong PL emission. Also, a very different InN crystal habit was observed for either case. The short nitridation cool-down was conducive to the formation of a continuous layer consisting mostly of coalesced downward-pointing hexagonal pyramids, while the long one led to a layer of upward-pointing hexagonal pyramids. The local decomposition of an AlON layer produced by sapphire nitridation and variations in the InAlN surface morphology resulting in a preferential attraction of growth species and localised change in the surface free energy contributions were most likely responsible for these observations. Our results also suggest N-polar buffer layers are likely to produce coalesced InN layers with a high electron mobility, while metal-polar buffer layers may facilitate the growth of high crystal quality pyramidal InN with a strong optical response.