Growth and Properties of Nearly Atomically-Flat Single Crystal Diamond Prepared by Plasma-Enhanced Chemical Vapor Deposition and its Surface Interactions

Abstract

This thesis deals with the study of the fundamental growth mechanism of homoepitaxial CVD diamond films using the microwave plasma enhanced chemical vapour deposition (MW PECVD) technique and aiming at depositing high quality intrinsic single crystal diamond, as well as at studying the incorporation of defects. The precise control over the microscopic growth mechanism leads to the minimization of crystallographic imperfections and results in the preparation of diamond crystals with nearly atomically-flat surfaces by mastering the reactions occurring at the growing (100) diamond surface. The spectroscopic study of defects incorporated in the homoepitaxial diamond films, their electrical transport measurements are discussed. Process parameters domain mapping at high plasma densities and relatively high gas pressures (~180 Torr), using specifically designed plasma configuration including the substrate holder optimization are described. The results obtained suggest that at high CH4 concentrations and at relatively low growth temperature the diamond (100) growth does not proceed via a generally accepted step flow growth mechanism but leads to an increased probability of a direct carbon radical add-addition to the surface atoms and progresses at many sites leading to nanosized clusters being formed onto the surface instead of only atomic steps. These nano-sized structures are present onto the surface almost independently of the growth time and are related to the specific growth mode used. The homoepitaxial diamond films grown at these conditions have been investigated in details with high resolution AFM and atomic resolution STM methods. Substrate quality and particularly developed specific surface O2/H2 treatments allowing reduction of crystallographic defects incorporated in the films and originating from the substrate are considered to have a major influence on the perfection of the films grown. These findings enable formation of near-atomically smooth thick films. Bulk defects, impurities and their incorporation to the diamond films have been monitored by defect spectroscopy techniques such as PL, Raman, CL, PC, and EPR. The main defect structures have been traced up in the films grown, related to the impurities such as N, B, Si, H and other elements, which incorporation could be altered by the plasma conditions and gas purity. Studies of the electrical transport of the (100) homoepitaxial layers have been expanded by the use of TOF technique. The electrical transport properties of freestanding homoepitaxial diamond films have been measured. In non- optimized samples there is a dispersive transport due to trapping of charge on defects present in the films, as also confirmed by spectroscopic methods. However, the best quality samples grown using high purity gases and optimized growth conditions have shown good electrical properties with high mobilities for electrons and holes.