Polarity control of ZnO films grown on nitrided c-sapphire by molecular-beam epitaxy

Abstract

The polarity of molecular-beam epitaxy grown ZnO films was controlled on nitrided c-sapphire substrate by modifying the interface between the ZnO buffer layer and the nitrided sapphire. The ZnO film grown on nitrided sapphire was proven to be Zn-polar while the O-polar one was obtained by using gallium predeposition on nitrided sapphire, which was confirmed by coaxial impact collision ion scattering spectroscopy and chemical etching effect. The Zn-polar ZnO film showed higher growth rate, slightly better quality, and different surface morphology in comparison to the O-polar one.

Cubic nitridation layers on sapphire substrate and their role in polarity selection of ZnO films

“…Based on this result, they concluded that the AlN layer is essential for the growth of the Ga-polar GaN films. Wang et al 11 showed that a N-polar AlN film was formed after the nitridation at 400°C, and the Zn polarity of their ZnO films was attributed to an amorphous ZnO wetting layer which inverts the polarity. As far as we know, no sufficiently nitrided layer with an ordered structure, however, has been achieved when nitridation temperature is below 400°C.…”

“…In previous reports, sapphire substrate nitridation is usually used to obtain high-quality GaN or ZnO films and control their polarity. [5][6][7][8][9][10][11] However, the understanding of sapphire nitridation mechanism is still very limited, and little attention has been paid to the microstructure of nitridation layers and its effects on polarity of subsequent GaN or ZnO epitaxial films since it is very difficult to obtain a nitridation layer with well-defined structure. Mikroulis et al 10 reported a 1.5 nm thick nitridation layer formed at 750°C, and an undetectable layer at 200°C.…”

Structural Evaluation of β-AlN Films Grown on Sapphire (0001) Substrates

“…And the depositions by vacuum arc deposition [18], pulse laser deposition (PLD) [10,11], and dual-cathode DC magnetron sputtering have employed Si(100), Si(100) and (111), and TiN/MgO(001), respectively. On the other hand, hexagonal sapphire has been employed for depositions by carbothermal reduction method [19], RF plasma-assisted molecular beam epitaxy [20,21], and nitrogen RF plasma source [22].…”

Structural and Mechanical Properties of Radiofrequency Ar-N2 Plasma Nitrided Aluminium

“…Owing to fabrication difficulties of such films and experimental verifications, applications to industrial devices have poorly been implemented yet. Only the growth of ultra-thin films or small crystallites have been reported in recent past 10,[13][14][15] . Plasma nitriding is one of the most favored methods having diversity in selecting process parameters including plasma composition, discharge frequency, fill pressure, input electrical power, substrate temperature and processing time.…”

“…In addition, c-AlN films are expected as buffer layers for polarity control in the growth of semiconductor films such as GaN and ZnO 10 . However, the synthesis of c-AlN is more tricky than α-AlN 11,12 .…”