Deposition and characterization of polycrystalline doped diamond by hot filament chemical vapor deposition

Hot Filament Chemical Vapor Deposition (HFCVD) has been used to grow polycrystalline diamond films on silicon substrates using H2/CH 4 gas mixtures. A brief overview of the crystal, thermal, optical and electronics properties of diamond are discussed. Diamond growth using HFCVD and the difficulty of depositing n-type doped diamond are discussed. The experimental set-up of the HFCVD and the challenges in having a uniform temperature over the substrate are presented. The diamond films thus formed were analyzed using Raman Spectra and show a diamond peak at 1332+/-2 cm-1. The surface is further analyzed by scanning electron microscopy and X-ray diffraction. X-ray Photon Spectroscopy (XPS) was used to determine the chemical state of the dopants on the diamond surface. A large number of samples of diamond films were successfully deposited on silicon substrates and we were able to identify an optimum methane to hydrogen ratio for good quality diamond (1.6% H2-900Sccm, CH4-15Sccm). Also we were able to successfully dope the diamond film p-type with boron using trimethyl borate diluted in acetone and n-type with phosphorous using trimethyl phosphite diluted in acetone. The electrical characteristics of the doped film were studied by depositing indium as a top metal contact. The combination of top side indium and back side aluminum on a p-type Si substrate resulted in ohmic contacts with slight non-linearity. Diamond P/N junction diodes were formed by growing a boron-doped diamond layer on a phosphorous-doped layer on a silicon substrate. The diodes showed rectification at room temperature and the diode characteristic was confirmed to occur at the interface between the n- and p-type diamond layers.