Epitaxial growth and interfaces of high-quality InN films grown on nitrided sapphire substrates
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Junning Gao State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, China
Junqiu Guo and Guoqiang Lia) Department of Electronic Materials, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China (Received 16 November 2012; accepted 26 February 2013)
InN films have been grown on sapphire substrates nitrided by N plasma with different durations by radio-frequency plasma assisted molecular beam epitaxy (RF-MBE). In-depth investigation reveals that AlN is generated on a sapphire surface during the nitridation, and 60 min nitridation helps in the formation of an ordered and flat AlN interlayer between the substrate and the InN film, which improves the surface migration of In atoms on the substrate, and consequently helps in obtaining a single-crystalline c-plane InN film of high quality with 1.0 1019 cm3 carrier density and 1350 cm2/(Vs) carrier mobility. Too short nitridation duration will result in a polycrystalline InN film, and too long nitridation duration will damage the surface quality of the newly generated AlN interlayer which consequently deteriorates the InN film quality. Control of the AlN interlayer quality plays a critical role in the growth of a high-quality InN epitaxial film on the sapphire substrate.
I. INTRODUCTION
Indium nitride (InN) has attracted considerable attention recently because of its outstanding electrical and optical properties. Among III-nitride semiconductors, InN has the lowest electron effective mass, the highest peak-drift velocity and the highest peak overshoot velocity, which are beneficial for high-electron-mobility transistors (HEMTs).1,2 Moreover, InN has a direct band gap of ;0.7 eV which enables the III-nitride semiconductors to cover the wave length from deep ultraviolet (AlN, Eg 5 6.2 eV) to near infrared (InN, Eg 5 0.7 eV).3,4 InN has shown great potential in the fields of terahertz emitters,5–8 light-emitting9 and photovoltaic applications,10 etc. In 1972, Hovel and Cuomo11 grew InN thin films on sapphire by using radio-frequency sputtering for the first time. With the development of thin film growth technology, researchers have obtained InN thin films using various techniques, such as hydride vapor phase epitaxy (HVPE),12 metal organic chemical vapor deposition (MOCVD),13 radio frequency plasma assisted molecular-beam epitaxy (RF-MBE),14 pulsed laser deposition (PLD),15,16 etc. However, it is still difficult to obtain high-quality InN due to its high equilibrium vapor pressure, low dissociation a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2013.67 J. Mater. Res., Vol. 28, No. 9, May 14, 2013
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temperature of nitrogen and the lack of suitable substrates for InN.17 To date, sapphire is the most common substrate to grow III-nitride semiconductors. However, InN shares an up to 25% mismatch with sapphire in terms of lattice parameter which results in polycrystalline InN films wh
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