Chapter 5 N-type diamond growth

Abstract

Summary n-Type diamond growth was one of the most difficult theme in the diamond research field. We have succeeded to obtain n-type diamond by doping phosphorus during CVD diamond growth on {111} diamond surface under well-optimized growth condition for high crystalline perfection diamond thin films. The surface of P-doped diamond surface is smooth with a characteristic morphology that convinces step-flow-mode growth is proceeding. Doping efficiency of P atoms was 3–4%. From RT to over 600 °C, the P-doped diamond thin films shown clear n-type characteristics as confirmed by Hall measurements. At present, the maximum doping concentration is about 5×10 19 cm −3 , and over the concentration of 10 19 cm −3 , hopping conductivity is observed at RT as dominant carrier transportation mechanism. For lower P-concentration films, clear thermal activation of the carriers has been observed and the activation energy was 0.6 eV which is consistent with the other characterization results obtained from FTIR and photocurrent measurements. Even for the heavily doped films, the thermally activated characteristic has been observed at high temperatures nominally over 400 K. The compensation ratio is as low as 1.5%. Characteristic luminescence spectrum has been obtained by CL analysis which atrributes bound exciton recombination related to P atoms. At RT, the freeexciton recombination has been observed that convinces high crystalline perfection of P-doped diamond thin films grown in the present study. A clear diode characteristic has been oserved from pn junction formed with the present P-doped diamond thin film grown on B-doped p-type diamond thin film. The rectification ratio was 10 8 –10 10 at RT. The light emission was observed with the diode operated with forward biasing of around 25 V. The spectrum showed the appearance of sharp UV light emission at 235 nm (5.27 eV) that attributes free exciton recombination coupled with TO phonon. The spectrum was also involved with broadband emissions caused by impurity and crystalline defects. To get monochromatic UV light emission from diamond pn junction, it is required to improve the crystalline perfection of boron-doped films.