Microscopic observation of lateral and vertical charge transportation in Si nanocrystals sandwiched by amorphous SiC layers

Jie Xu,Yang Ji,Jun Xu,Gang Bai,Qingying Ren,Peng Lu

doi:10.1063/1.5020239

Abstract

Charge injection and transportation process is a fundamental problem to Si nanocrystals (Si-ncs) based electric and photonic devices. In the manuscript, a single layer of Si-ncs sandwiched by amorphous Si carbide (a-SiC) was prepared by excimer laser annealing of a-SiC/a-Si/a-SiC multilayers, and the charging effect was then characterized by Kelvin probe force microscopy (KPFM) on the microscopic scale. Opposite charges were injected into Si-ncs through the biased tip and formed a core-ring or up-down shaped distribution. The decay characteristics showed that these opposite charges would not only vertically tunnel through the bottom a-SiC layer to substrate but also laterally transport and recombine with each other driven by the attractive Coulomb force. Besides, the charge retention time was also found dependent on the injection biases, which is tentatively ascribed to the charge trapping by the Si-ncs/a-SiC interface states under high bias scanning. The analysis was further supported by conductive atomic force microscopy (CAFM) measurement, in which the current-voltage curves gradually shifted during the repetition test, probably because of bias screening by the trapped charges at these interface states.

Highlights

Si nanocrystals (Si-ncs) based material is promising to construct low-cost light emitting diodes,[1,2] high efficient photovoltaic devices,[3,4] floating gate memories[5,6] and other optical structures,[7,8] due to the quantum confinement effect and novel interface or surface properties
It should be mentioned here that since the Kelvin probe force microscopy (KPFM) measurement is based on a two-pass scan technique, there exists a problem of charge evacuation through the tip during the first-pass scan
When the tip scans the charged sample without external bias in our KPFM measurement, charge evacuation through the tip was thought not the main leakage channel owing to the sample structure and the parameter setting during the first-pass scan

Summary

INTRODUCTION

Si nanocrystals (Si-ncs) based material is promising to construct low-cost light emitting diodes,[1,2] high efficient photovoltaic devices,[3,4] floating gate memories[5,6] and other optical structures,[7,8] due to the quantum confinement effect and novel interface or surface properties. In these electronic and photonic devices, charge transportation and recombination property is a fundamental issue and need to be deeply understood. The charging effect of the sample was found dependent on the injection biases, probably due to charge trapping by the Si-ncs/a-SiC interface states during high bias scanning

EXPERIMENTAL

RESULTS AND DISCUSSION

CONCLUSIONS