Is it permissible for me to receive extra money for extra work by creating a false voucher?

I’m serving as a Computer Operator in a government office. but I have no permanent post here. My salary are fixed and my duty time is 9.00AM to 5.00PM. But some officers work at 9.00AM to 8.00PM or more. For that reason they need a computer operator with them at 9AM to 8PM or more. Now they want I stay with them and that cause they will pay me extra money. They have no provision to give this money that way. But they have lots of money to use for varieties work. Now they give permission to make a false Voucher and take this money to use this voucher. My questions is: every month i give them a false voucher to get this money (for my extra duty). Is this money Halal for me.