Approaches for phosphorus incorporation on (100) oriented diamond surfaces

Diamond based electronics, in particular for high power, high frequency and harsh ambients are evolving more rapidly in part due to the availability of high-quality substrates with increasing size. A more economical device fabrication can be achieved for larger wafers and with a (100) oriented surface. However, prominent device demonstrations for p-i-n diodes and bi-polar junction transistors utilized (111) substrates as sufficiently high phosphorus incorporation for the n-type layer is more readily achieved. We present an approach for phosphorus doping of (100) oriented surfaces that utilizes in-situ monitoring of the gas chemistry via residual gas analysis (RGA) during a pulsed deposition technique. An ASTeX style, plasma enhanced chemical vapor deposition (PECVD) system was equipped with an RGA system to monitor and control in real-time the gas chemistry during growth. Results established that the concentration of PH radicals during plasma growth was related to the incorporated phosphorus concentration. Doped diamond growth was performed on CVD type IIa (100) diamond substrates with a surface finish of 5nm Ra. Process gases included hydrogen, methane and a 200ppm trimethylphosphine (TMP) in hydrogen gas mixture. The pulsed deposition technique included growth steps separated by cooling steps where the growth process was interrupted. With optimized conditions a phosphorus concentration approaching 10¹⁹cm^-3 was measured by secondary ion mass spectroscopy (SIMS) with an abrupt doping gradient. The doping results will be described in terms of the surface chemistry and the pulsed growth technique. Improvements in phosphorus doping will be discussed in terms of miscut, growth mode (step-bunching), surface finish and surface pre-treatment processes.<br/>This research was support by the NSF through grant DMR-2003567 and the U.S. Department of Energy, Office of Science, Basic Energy Sciences through ULTRA, an Energy Frontier Research Center under Award #DE-SC0021230.