Selective heteroepitaxial growth of germanium for monolithic integration of MOSFETs and optical devices.

摘要

As Si bulk CMOS devices approach their fundamental scaling limit, diverse research is being done to introduce novel structures and materials. High carrier mobility and possible monolithic integration with Si based devices have prompted renewed interest in Ge based devices. For optical applications, it was challenging to make photodetectors operate in 1.3-1.55microm wavelength range with Si, due to its relatively large indirect (1.1eV) and direct (3.4eV) bandgaps. However, Ge's smaller direct band gap (0.8eV) corresponding to ∼1.55microm in wavelength and possible monolithic integration with Si CMOS technology make Ge a strong candidate for photodetectors.;In the first part of the thesis, selective Ge heteroepitaxial growth on Si and in-situ doping technique for n+/p junction are discussed. Surface roughness of heteroepitaxially gorwn Ge on Si is considerably reduced by high temperature hydrogen annealing. Ge growth and hydrogen annealing steps are repeated until desired epi layer thickness is reached. High quality Ge film (minimal dislocation (1x107cm-2) and very smooth surface (0.65nm (RMS)) is achieved selectively on Si using SiO2 window. For abrupt and box shaped n+/p junction in Ge, in-situ phosphorus doping using PH3 is employed during the epitaxial growth. Temperature dependency of the dopant activation was investigated associated with the shallower and abrupt junction formation. Novel n+/p diodes show better characteristics (on/off ratio and on current density) compared with conventional ion-implanted junction.;High performance Ge MOSFETs and optic devices fabricated using selective Ge heteroepitaxial growth on Si are discussed in the second part of the thesis. For n-MOSFETs, in-situ doping technique is used to form source and drain with very low series resistance and shallow junctions. p-MOSFETs are fabricated with high-k/metal gate stack. Results show the highest electron mobility ever reported on (100) Ge n-MOSFETs and ∼80% enhancement of hole mobility over Si universal mobility for p-MOSFETs. Normal incidence p-i-n photodiodes on selectively grown Ge are also demonstrated. Enhanced efficiency in the near infrared regime and the absorption edge shifting to longer wavelength is achieved due to residual tensile strain. Measured responsivities are promising towards monolithically integrated on-chip optical links and in telecommunications.;In this study, we demonstrate high performance Ge MOSFETs and optical devices which can be monolithically integrated to Si technology, by employing novel Ge heteroepitaxial growth and in-situ dopoing technique.