Crystalline Defects Induced during MPCVD Lateral Homoepitaxial Diamond Growth.

Fernando Lloret,David Eon,Daniel Araujo,Etienne Bustarret

doi:10.3390/nano8100814

Abstract

The development of new power devices taking full advantage of the potential of diamond has prompted the design of innovative 3D structures. This implies the overgrowth towards various crystallographic orientations. To understand the consequences of such growth geometries on the defects generation, a Transmission Electron Microscopy (TEM) study of overgrown, mesa-patterned, homoepitaxial, microwave-plasma-enhanced, chemical vapor deposition (MPCVD) diamond is presented. Samples have been grown under quite different conditions of doping and methane concentration in order to identify and distinguish the factors involved in the defects generation. TEM is used to reveal threading dislocations and planar defects. Sources of dislocation generation have been evidenced: (i) doping level versus growth plane, and (ii) methane concentration. The first source of dislocations was shown to generate <110> Burgers vector dislocations above a critical boron concentration, while the second induces <112> type Burgers vector above a critical methane/hydrogen molar ratio. The latter is attributed to partial dislocations whose origin is related to the dissociation of perfect ones by a Shockley process. This dissociation generated stacking faults that likely resulted in penetration twins, which were also observed on these samples. Lateral growth performed at low methane and boron content did not exhibit any dislocation.

Highlights

Defects in diamond are still one of the main restrictions for the development of commercial diamond electronics [1]
The study by Transmission Electron Microscopy (TEM) of the lateral diamond growth over 3D patterns has pointed out many lattice-related defects on the studied samples that can be attributed to lattice strain at the corners of trenches and mesa rectangle structures, or to additional surface effects [18,22]
Electronics grade, {001}-oriented, high pressure-high temperature (HPHT) diamond substrates have been etched by inductively coupled plasma reactive ion etching (ICP-RIE) using pure O2 gas, leaving a set of 0.8/1 μm height mesa-shaped cylindrical patterns

Summary

Introduction

Defects in diamond are still one of the main restrictions for the development of commercial diamond electronics [1]. Many works have studied this topic in the case of 2D diamond growth [7,8,9] contributing to significantly improving the growth of diamond films and the control of the doping level to the point where the fabrication of δ-doped diamond layers could be contemplated [6,9,10,11,12,13]. The design of alternative structures will allow to overcome these difficulties [17] In this direction, overgrowth on mesa-etched substrate is being used to manage local doping in order to design three dimensional devices [18,19], as well as to improve the local surface roughness of homoepitaxial diamond films [20,21], or to reduce the density of threading dislocations. To identify the crucial parameters that should be controlled to avoid such defects, and to understand the mechanisms responsible for the generation of dislocations, seven samples were grown on mesa-etched substrates under different conditions of pressure, temperature, doping and/or methane concentration (see Table 1), and studied by TEM in diffraction contrast mode

Methods

Findings

Discussion

Conclusion