Joining P- and N-Type Germanium

Date: 2015-10-07; view: 513.

Text B

Like N-type germanium, P-type germanium is also electrically neutral (Fig. 1).

When N-type germanium and P-type germanium are joined some electrons and holes combine at the junction. In the region of the junction, N-type germanium loses some of its electrons. Thus, it is no longer neutral in this area; it now has a positive charge. The electrons it loses, combine with holes from P-type germanium at the junction. The P-type germanium becomes negative. The majority car­riers have combined at the junction, leaving charged atoms (ions) in the area near the junction. A potential difference (of the order of several tenths of a volt) exists between the N- and P-type germanium ions. If more electrons try to move from the N-type to the P-type, they are stopped by the negatively charged ions in the P-type germanium near the junction (Fig. 2). In a similar fashion holes from the P-type are prevented from crossing the junction by the building up of positively charged ions in the N-type germanium. The net effect of this action is to set up a barrier voltage that prevents further combination of electrons and holes. The area in which this voltage exists is called the barrier region.

Fig. 1Doped germanium is electrically neutral	Fig. 2Electrons are stopped near the junction