FileStream fs = new FileStream(@"c:\test.prg", FileMode.Create, FileAccess.Write, FileShare.None);

UInt16 ui1 = 1;
char ch1 = Convert.ToChar(ui1);
UInt16 ui2 = 220;
char ch2 = Convert.ToChar(ui2);
UnicodeEncoding enc = new UnicodeEncoding(true, false);
char[] c = new char[2];
c[0] = ch1;
c[1] = ch2;

using (StreamWriter sw = new StreamWriter(fs))
{
  sw.Write(enc.GetBytes(c));
  sw.Write(c);
}