Nucleation and growth surface conductivity of H-terminated diamond films prepared by DC arc jet CVD

Abstract

High-quality polycrystalline diamond film has been extremely attractive to many researchers, since the maximum transition frequency (fT) and the maximum frequency of oscillation (fmax) of polycrystalline diamond electronic devices are comparable to those of single crystalline diamond devices. Besides large deposition area, DC arc jet CVD diamond films with high deposition rate and high quality are one choice for electronic device industrialization. Four inch free-standing diamond films were obtained by DC arc jet CVD using gas recycling mode with deposition rate of 14μm/h. After treatment in hydrogen plasma under the same conditions for both the nucleation and growth sides, the conductivity difference between them was analyzed and clarified by characterizing the grain size, surface profile, crystalline quality and impurity content. The roughness of growth surface with the grain size about 400nm increased from 0.869nm to 8.406nm after hydrogen plasma etching. As for the nucleation surface, the grain size was about 100nm and the roughness increased from 0.31nm to 3.739nm. The XPS results showed that H-termination had been formed and energy band bent upwards. The nucleation and growth surfaces displayed the same magnitude of square resistance (Rs). The mobility and the sheet carrier concentration of the nucleation surface were 0.898cm/Vs and 1013/cm2 order of magnitude, respectively; while for growth surface, they were 20.2cm/Vs and 9.97×1011/cm2, respectively. The small grain size and much non-diamond carbon at grain boundary resulted in lower carrier mobility on the nucleation surface. The high concentration of impurity nitrogen may explain the low sheet carrier concentration on the growth surface. The maximum drain current density and the maximum transconductance (gm) for MESFET with gate length LG of 2μm on H-terminated diamond growth surface was 22.5mA/mm and 4mS/mm, respectively. The device performance can be further improved by using diamond films with larger grains and optimizing device fabrication techniques.