1. D.J. Griffiths, Introduction to Quantum Mechanics (Pearson Education Ltd., New York, 2005)
2. E. Merzbacher, Quantum Mechanics (John Wiley and Sons, New York, 1998)
3. V.E. Lashkaryov, Izv. Akad. Nauk SSSR Ser. Fiz. 5, 442 (1941)
4. R.S. Ohl, U.S. Patent 2402662 (Filed May 27, 1941, Issued June 25, 1946)
5. W. Shockley, Bell Syst. Tech. J. 28, 435 (1949)