Semiconductor crystals doped with electron-deficient impurities such as Group 13 elements B, Al or Ga which contain only 3 valence electrons. The fourth missing electron spot is called the electron vacancy or electron hole. An electron from the neighbouring atom can come and fill up the vacancy, leaving a vacancy in its original position. On application of an electric field, the holes will appear to move in the direction opposite to the direction of the electrons. The dislocated electrons move towards the positive plate, the holes move towards the negative plate. These type of semiconductors are known as p-type semiconductors, p being positive. Option (iii) is impossible to occur, hence (i), (ii) and (iv) are correct statements.