Microscopic study of electrical properties of CrSi2 nanocrystals in silicon

László Dózsa,Nikolay Gennadevich Galkin,Filippo Giannazzo,Štefan Lányi,Vito Raineri

doi:10.1186/1556-276x-6-209

Abstract

Semiconducting CrSi2 nanocrystallites (NCs) were grown by reactive deposition epitaxy of Cr onto n-type silicon and covered with a 50-nm epitaxial silicon cap. Two types of samples were investigated: in one of them, the NCs were localized near the deposition depth, and in the other they migrated near the surface. The electrical characteristics were investigated in Schottky junctions by current-voltage and capacitance-voltage measurements. Atomic force microscopy (AFM), conductive AFM and scanning probe capacitance microscopy (SCM) were applied to reveal morphology and local electrical properties. The scanning probe methods yielded specific information, and tapping-mode AFM has shown up to 13-nm-high large-area protrusions not seen in the contact-mode AFM. The electrical interaction of the vibrating scanning tip results in virtual deformation of the surface. SCM has revealed NCs deep below the surface not seen by AFM. The electrically active probe yielded significantly better spatial resolution than AFM. The conductive AFM measurements have shown that the Cr-related point defects near the surface are responsible for the leakage of the macroscopic Schottky junctions, and also that NCs near the surface are sensitive to the mechanical and electrical stress induced by the scanning probe.

Highlights

Chromium disilicide (CrSi2) is a narrow band semiconductor (Eg = 0.35 eV [1]), which can be epitaxially grown on Si (111) [2]
The samples with NCs migrating near the surface show high concentration of donors, while in samples with NCs remaining near 50-nm deposition depth, the donor concentration is low
Electrical characteristics of monolithic Si/CrSi2 NCs/Si structures with different depth distributions of the NCs were investigated in large-area Schottky junctions by I-V and C-V measurements, and locally by scanning probe techniques, conductive Atomic force microscopy (AFM) and scanning probe capacitance microscopy (SCM)

Summary

Introduction

50 nm silicon cap was grown by MBE at 700°C at deposition rate of 3-4 nm/min over the NCs. The morphology was studied by atomic force microscopy (AFM) in contact and tapping-mode. Results and discussion XTEM measurements have shown that the CrSi2 NCs migrate towards the surface during the cap growth [6,8]. The markedly different concentrations of Crrelated point defect in the two types of samples indicate that these defects may be related to the observed migration of the NCs during the cap growth.

Results

Conclusion