Semiconductor Theory and Devices 271 We now have the situation whereby there will be more mobile holes than there are free electrons. Since holes are positive charge carriers, and they will be in the majority, the doped material is called p-type semiconductor, and it may be considered as consisting of a number of ﬁ xed negative ions and a corresponding number of mobile holes as shown in Fig. 9.8 . e–h pairfixednegativeionmobilehole Fig. 9.8 holeselectronsI Fig. 9.9 The circuit action when a battery is connected across the material is shown in Fig. 9.9 . As the holes approach the left-hand end they are ﬁ lled by incoming electrons from the battery. At the same time, fresh electron-hole pairs are generated; the electrons being swept to and out of the right-hand end, and the holes drift to the left-hand end to be ﬁ lled. Once more, the current ﬂ ow in the semiconductor is due to the movement of holes and electrons in opposite directions, and only electrons in the external circuit. As with the n-type material, p-type is also electrically neutral. 9.8 The p-n Junction When a sample of silicon is doped with both donor and acceptor impurities so as to form a region of p-type and a second region of n-type material in the same crystal lattice , the boundary where the two regions meet is called a p-n junction. This is illustrated in Fig. 9.10 .