Suppression of Al Memory-Effect on Growing 4H-SiC Epilayers by Hot-Wall Chemical Vapor Deposition

Abstract

The study of the parameters' distribution along the channel axis in a stationary plasma thruster(SPT) helps one to understand the physical characteristics of the SPT's operation. In this paper, the axial distribution of the desired SPT parameters are predicted by combining the improved scaling theory and a one-dimensional hybrid model. The simulation indicates that the SPT parameters' distribution along the channel axis changes with scaling index variable C. If C is set properly, the similarity of the parameters' axial distribution between the model and a desired thruster can be ensured. In addition, the operation characteristics of the desired thruster, such as the ionization and acceleration processes, are also similar to those of the model. When C is set, the improved SPT scaling theory and the one-dimensional hybrid model can be used to predict the axial distribution of the desired SPT parameters with the same propellant (such as Xe).

Suppressing Al memory effect on CVD growth of 4H-SiC epilayers by adding hydrogen chloride gas

“…Therefore, we performed site-competition growth (Si-rich) to further reduce Al impurity level by hindering Al atom incorporation during the undoped epilayer growth. 7,[12][13][14][15] Undoped epilayers were grown at C/Si = 0.2-0.8, with a 5 min HCl flushing inserted between the epilayers growth at the HCl flow rates of 20, 200, and 400 sccm. To minimize the effect of residual HCl gas on the following undoped epilayer growth, there was an additional waiting period (only H 2 in) of 3-5 min to purge the remaining HCl gas in the reactor.…”

“…Much research effort has been made to suppress the Al memory effect. [7][8][9][10][11] We have studied the suppression methods using site-competition growth and achieved a reduction factor (the ratio of Al concentration N Al in the undoped epilayer to that in the p + layer) of about 1/17,000, e.g., N Al from 9 © 10 19 to 6 © 10 15 cm ¹3 or from 1.7 © 10 20 to 1.0 © 10 16 cm ¹3 . 7) On the other hand, La Via et al reported that the growth using trichlorosilane can decrease the Al impurity level to 10 14 cm ¹3 after a p + epilayer growth with N Al ³ 1 © 10 18 cm ¹3 , but it is a concern that there may be an upper limit of Al doping level of approximately 10 18 cm ¹3 .…”

“…[7][8][9][10][11] We have studied the suppression methods using site-competition growth and achieved a reduction factor (the ratio of Al concentration N Al in the undoped epilayer to that in the p + layer) of about 1/17,000, e.g., N Al from 9 © 10 19 to 6 © 10 15 cm ¹3 or from 1.7 © 10 20 to 1.0 © 10 16 cm ¹3 . 7) On the other hand, La Via et al reported that the growth using trichlorosilane can decrease the Al impurity level to 10 14 cm ¹3 after a p + epilayer growth with N Al ³ 1 © 10 18 cm ¹3 , but it is a concern that there may be an upper limit of Al doping level of approximately 10 18 cm ¹3 . 8) Nordell et al tried to suppress unintentional Al doping by HCl flushing at various C/Si ratios, and they obtained abrupt changes in Al distributions, e.g., N Al at the surface epilayers, 10 19 to 2 © 10 15 cm ¹3 ; inner layers, 1.5 © 10 20 to 7 © 10 15 cm ¹3 .…”

“…In this study, we attempted to develop a method of forming the following undoped epilayer with an extremely low Al impurity level (³10 14 cm ¹3 ) immediately after a heavily Al-doped epilayer growth (³10 20 cm ¹3 ) on the basis of the previous findings on site-competition growth, 7,[12][13][14][15] and the possibility of very low unintentional doping in the presence of chlorine species. 11,[16][17][18] HCl gas was introduced into the CVD growth process by three methods, and the Al suppression efficiency in relation to the input C/Si ratio was studied.…”

Study of nanostructures and interfaces of technological materials by means of electron microscopy techniques

“…Regarding the as called "memory effect" in MOCVD, described in literature [142], [143], it is very much different from this case. Memory effect refers to abrupt change in gas-phase composition during growth, i.e when growing GaN:Mg (Mg-doped, with Ga/Mg ratio usually <1000) followed by undoped GaN (without intentional doping, Mg-is off).…”