Eradicated unintentional incorporated donor-type impurities of ZnO

Xiuhua Xie,Dezhen Shen,Zhenzhong Zhang,Binghui Li

doi:10.1063/1.5022998

Abstract

Impurity control is essential for semiconductor doping. Through the systematic analysis of pollution sources, we determined that the residual electrons of as-grown unintentional doped zinc oxide (ZnO) films were derived from the unintentional incorporation of silicon, which grown by molecular beam epitaxy. At the same time, it was determined that unforeseen donor-type impurities (boron, carbon, chlorine and fluorine) were introduced during the nitrogen doping process. By subjecting the sources of the contamination to a surface passivation process, these donor-type impurities are controlled at a tolerable level. The residual electrons concentration of the unintentional doped ZnO film was lowered to 1 × 1015 cm-3, and the mobility was 155 cm2/V·s. Nitrogen-doped ZnO films exhibited p-type conductivity, with a hole concentration of 2 × 1016 cm-3 and a mobility of 10 cm2/V·s. Our results provide a pure foundation for further research on p-type doping of ZnO.

Highlights

The desire for p-type zinc oxide (ZnO) has been a top priority for ZnO-based ultraviolet optoelectronics research.[1,2] We know that the premise of obtaining p-type ZnO is the effective doping
Unintentional doped and nitrogen (N) doped ZnO films were grown in molecular beam epitaxy (MBE) system (Finland DCA P-600), which equipped with solid-source effusion cells for zinc (Zn) and oxford radiofrequency (RF) atom source (HD25, operating frequency of 13.56 MHz) for active O and N
The gas was delivered to the electrical discharge space which surrounded by discharge tube (DT) and aperture plate (AP)

Summary

INTRODUCTION

The desire for p-type zinc oxide (ZnO) has been a top priority for ZnO-based ultraviolet optoelectronics research.[1,2] We know that the premise of obtaining p-type ZnO is the effective doping. Unintentional doped ZnO films have a residual electrons concentration of about 1 × 1016 cm-3,3–5 which indicating that there are more donors exist. The native point defects, zinc interstitials (Zni) and oxygen vacancies (V O), were considered the donors of residual electrons.[6,7,8] according to the theoretical calculation and the experimental results,[9,10,11] the V O are the deeper donors which can not effectively ionize, while the Zni have lower migration barrier, so that they are not stable at room temperature. It is necessary to reanalyze the n-type conductivity of ZnO thin films based on experimental evidence. Unintentional incorporated donor-type impurities have been suppressed via pollution sources surface passivation

EXPERIMENTAL DETAILS

RESULTS AND DISCUSSION

CONCLUSIONS