Electron cyclotron resonance hydrogen plasma and argon plasma was used to clean Si surface without additional heating within 4 min and 30 s, respectively. Changes in the electrical properties after plasma treatment with different exposure times have been studied and compared using a Schottky diode structure. The reverse saturation current of the Schottky diodes changes less in the case of the hydrogen plasma cleaned samples than the argon plasma cleaned samples. After hydrogen plasma exposure, residual hydrogen introduced into the Si was found to enhance greatly the formation of thermal donors which induces considerable changes in the defect states after annealing. After annealing at similar to 450 degrees C in N-2, new defects, caused by thermal donors, appear and these defects decrease significantly at 750 degrees C. Defects in the argon plasma treated samples annihilate after annealing at 1000 degrees C for 1 h.