Homoepitaxial Diamond Growth Initiation on Smooth CMP Surfaces at Various Mis-Cut Angles

Homoepitaxial diamond growth by microwave plasma-assisted CVD is used to grow both doped and intrinsic epilayers of diamond for electronic and quantum applications. Often when different doping types or concentrations are desired, the deposition is done in different diamond deposition systems due to avoiding doping memory effects in the deposition system. This requires that the growth process be re-initiated when the sample is moved to a different deposition system. The initiation of the growth process has been shown to often have defects at the growth initiation boundary as evidenced by optical microscopy, photoluminescence and/or cathodoluminescence. This study aims to investigate the growth process at the initiation of the diamond deposition to improve the boundary between different doped epilayers. An objective in many applications is to have abrupt junction between diamond doped with different concentrations or types.<br/><br/>Experiments were performed on the growth initiation on single crystal diamond substrates with various mis-cut angles from the (001) surface. The mis-cut angle was varied from 0 to 4 degrees as determined by X-ray diffraction measurements. To prepare the smooth diamond surface before growth the substrates were chemical mechanical polishing (CMP) polished to achieve a surface roughness of less than 0.3 nm RA. The CMP process was done by polishing the diamond substrate with a slurry of boron carbide, potassium permanganate, and phosphoric acid at a rate of about 100 nm/hr. The surface roughness was measured with AFM. Prior to CMP the substrate was mechanically polished on a Scaife, and the surface was then plasma etched to remove about 2 µm of diamond that may have polishing damage.<br/><br/>The diamond deposition was performed with a hydrogen, methane, and carbon dioxide feed gas mixture that gives a growth rate of 2-6 µm/hr. The diamond deposition was done with only a short time between deposition system turn on and growth initiation. This short time is important to minimize any surface etching/roughening before the growth starts. The growth was allowed to proceed for short periods of time so that 1-2 µm of diamond or less were grown. When the short growth is finished the surface is examined with AFM, optical microscopy, and SEM to look for island growth and step-terrace growth features as a function of the mis-cut angle. Also diamond deposition runs are done under the same growth conditions for various times to see how the growth surface evolves at the start.<br/><br/>The work has observed the smooth surface getting rougher at the initiation of the growth. We will report on the evolution of the surface versus growth time and mis-cut angle. For small mis-cut angles island-like growth occurs and we will quantify the growth of the island size versus growth time. For larger mis-cut angles the transition to step-flow growth will be quantified in terms of terrace and step size evolution. The steps will also be analyzed in terms of step facet height and direction. We will also look at the implications of the growth initiation on doping spatial uniformity in the grown layer.<br/><br/><b>Acknowledgement:</b> The Energy Frontier Research Center on Ultrawide Bandgap Materials (EFRC-UWBG) funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES) division under award number DE-SC0021230.<br/>&lt;quillbot-extension-portal&gt;&lt;/quillbot-extension-portal&gt;