Electron transport properties of degenerate n-type GaN prepared by pulsed sputtering

Kohei Ueno,Atsushi Kobayashi,Hiroshi Fujioka,Taiga Fudetani,Jitsuo Ohta,Yasuaki Arakawa

doi:10.1063/1.5008913

Abstract

We report a systematic investigation of the transport properties of highly degenerate electrons in Ge-doped and Si-doped GaN epilayers prepared using the pulsed sputtering deposition (PSD) technique. Secondary-ion mass spectrometry and Hall-effect measurements revealed that the doping efficiency of PSD n-type GaN is close to unity at electron concentrations as high as 5.1 × 1020 cm−3. A record low resistivity for n-type GaN of 0.16 mΩ cm was achieved with an electron mobility of 100 cm2 V−1 s−1 at a carrier concentration of 3.9 × 1020 cm−3. We explain this unusually high electron mobility of PSD n-type GaN within the framework of conventional scattering theory by modifying a parameter related to nonparabolicity of the conduction band. The Ge-doped GaN films show a slightly lower electron mobility compared with Si-doped films with the same carrier concentrations, which is likely a consequence of the formation of a small number of compensation centers. The excellent electrical properties presented in this letter clearly demonstrate the striking advantages of the low-temperature PSD technique for growing high-quality and highly conductive n-type GaN.

Highlights

The physics of degenerate electrons in a partially filled conduction band of heavily doped n-type GaN has been extensively investigated because of the importance for reducing the parasitic resistance of nitride optical and electron devices.[1,2,3] Si is the most commonly used dopant for n-type GaN, and a room-temperature (RT) free-electron concentration of 3.6 × 1020 cm3 has been achieved in Si-doped GaN deposited using molecular beam epitaxy (MBE).[3]
Despite the high free-electron concentration achieved by these techniques, the minimum resistivity of the GaN films remains high (0.3–0.4 mΩ cm) at electron concentrations of ∼2 × 1020 cm3,2,3 and the resistivity increases with increasing dopant concentration.[3,5]
The use of pulsed sputtering deposition (PSD) enables the growth of device-quality group-iii nitrides at much lower temperatures than those used in the conventional metal–organic chemical vapor deposition (MOCVD) process.[6,7,8,9,10,11]

Summary

Introduction

The physics of degenerate electrons in a partially filled conduction band of heavily doped n-type GaN has been extensively investigated because of the importance for reducing the parasitic resistance of nitride optical and electron devices.[1,2,3] Si is the most commonly used dopant for n-type GaN, and a room-temperature (RT) free-electron concentration of 3.6 × 1020 cm3 has been achieved in Si-doped GaN deposited using molecular beam epitaxy (MBE).[3]. Electron transport properties of degenerate n-type GaN prepared by pulsed sputtering

Results

Conclusion