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    The study of P-type and N-type diamond crystals synthesis by hot filament chemical vapor deposition
    (2017-11-03)
    Sodngam, Piyachat
    ;
    Niemcharoen, Surasak
    ;
    Titiroongraung, Wisut
    ;
    Siriwongrungson, Vilailuck
    This research proposes the hot filament chemical vapor deposition (HFCVD) for synthesis of p-type and n-type diamond by doping of boron trioxide (B<inf>2</inf>O<inf>3</inf>) and phosphorous pentoxide (P<inf>2</inf>O<inf>5</inf>) in ethyl alcohol (C<inf>2</inf>H<inf>5</inf>OH), respectively. The synthesis was conducted for 180 h with annealing under hydrogen atmosphere every 60 h to improve the quality of the diamond. Composition of the synthetic diamond was analyzed using energy-dispersive x-ray spectroscopy (EDX). The main composition of the synthetic diamond is boron and carbon, and phosphorous and carbon for boron-doped and phosphorous doped synthetic diamond crystal, respectively. The crystal size and physical characteristics were analyzed using scanning electron microscopy (SEM). The synthetic diamond as large as 1.56 mm and 1.63 mm was synthesized. In addition, the synthetic diamond was confirmed to be diamond using Raman spectroscopy. The peak at Raman shift of 1332 cm<sup>-1</sup> that is the same as the natural diamond was observed. Moreover, electrical properties of the synthetic diamond were compared with intrinsic diamond at similar crystal size. The conductivity of the boron-doped synthetic diamond shown positive side (p-type) and phosphorous-doped synthetic diamond shown negative side (n-type) from the measurement using hot probe. The resistance of the synthetic doped with B<inf>2</inf>O<inf>3</inf> and P<inf>2</inf>O<inf>5</inf> is 5.711 kΩ and 4.570 kΩ, respectively from the measurement using Circuit applied for current and voltage measurement. The resistances measured are significantly lower than intrinsic diamond. Therefore, it can be implied that the conductivity of the synthetic diamond is better than intrinsic diamond.
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    Development of Large Diamond Synthesis by Double Test Tubes Hot Filament Chemical Vapor Deposition
    (2017-01-01)
    Sodngam, Piyachat
    ;
    Meekluab, Prapassorn
    ;
    Siriwongrungson, Vilailuck
    ;
    Neamchalern, Surasak
    ;
    Titiroongraung, Wisut
    In this research, “diamond” synthesis device by double test tubes hot filament chemical vapor deposition (HFCVD) was developed and proposed. Remaining hydrogen was reused for the maximum utilization of resources. In addition, this diamond synthesis device is capable to synthesis diamond continuously of up to 60 h per time. As a result, large diamond as large as 1.85 mm and 1.73 mm can be produced from the synthesis of three times with 180 h in total. Moreover, after each synthesis, the quality of diamond crystal was improved by annealing in hydrogen atmosphere. The crystal size was measured and physical characteristics of diamond were analyzed using scanning electron microscopy (SEM). The increasing rate of diamond crystal size after each synthesis was also examined. In addition, electrical properties of the synthetic diamond was compared with natural diamond from room temperature (25°C) to 200°C. The synthetic diamond has the resistance of 1337.28 M?, which the natural diamond has the resistance of 1428.67 M?. Temperature changes has no effect on the resistance of the diamond crystal. Moreover, the synthetic diamond was confirmed to be diamond using Raman spectroscopy. It has the same peak as the natural diamond at the Raman shift of 1332 cm<sup>-1</sup>.