Single-Crystalline Si1−xGex (x = 0.5~1) Thin Films on Si (001) with Low Threading Dislocation Density Prepared by Low Temperature Molecular Beam Epitaxy

Gu Gu,Deng Deng,Zhao Zhao,Ye Ye,Lu Lu

doi:10.3390/app9091772

Abstract

Single-crystalline Si1−xGex thin films on Si (100) with low threading dislocation density (TDD) are highly desired for semiconductor industrials. It is challenging to suppress the TDD since there is a large mismatch (4.2%) between Ge and Si—it typically needs 106–107/cm2 TDD for strain relaxation, which could, however, cause device leakage under high voltage. Here, we grew Si1−xGex (x = 0.5–1) films on Si (001) by low temperature molecular beam epitaxy (LT-MBE) at 200 °C, which is much lower than the typical temperature of 450–600 °C. Encouragingly, the Si1−xGex thin films grown by LT-MBE have shown a dramatically reduced TDD down to the 103–104/cm2 level. Using transmission electron microscopy (TEM) with atomic resolution, we discovered a non-typical strain relaxation mechanism for epitaxial films grown by LT-MBE. There are multiple-layered structures being introduced along out-of-plane-direction during film growth, effectively relaxing the large strain through local shearing and subsequently leading to an order of magnitude lower TDD. We presented a model for the non-typical strain relaxation mechanism for Si1−xGex films grown on Si (001) by LT-MBE.

Highlights

Single-crystalline Si1−x Gex alloy films have been an important material system due to their tunable bandgaps, strains, and lattices, and they can be tuned to match III-V semiconductors [1,2]
We presented a model for the non-typical strain relaxation mechanism for Si1−x Gex films grown on Si
The threading dislocation density (TDD) in Si1−x Gex (x = 0.5–1) films grown on Si (001) can be controlled to the level of 106 –107 /cm2 [14]

Summary

Introduction

Single-crystalline Si1−x Gex alloy films have been an important material system due to their tunable bandgaps, strains, and lattices, and they can be tuned to match III-V semiconductors [1,2]. They have become a more attractive topic for several reasons, such as to integrate GeSn on Si to produce direct bandgap Si photonic devices and to produce high-frequency microwave devices on Si [3,4,5,6,7]. The LT-MBE (a few hundred degrees lower than the typical values [8]) was reported to be helpful for growing single-crystalline thin films with a high mismatch between substrate and the film [24,25]. TEM with atomic resolution has been used to characterize these films, and the film strain relaxation mechanism has been proposed

Materials and Methods

Results and Discussion

XRD spectra of series

Conclusions