Abstract
Semiconductors have a limited number of free electrons. Pure germanium conducts to a limited extent and to make it suitable for electrical purposes, a minute quantity of impurity must be introduced.. Arsenic has five free electrons; therefore, four of these would combine with the four valence electrons of germanium, leaving a 5th electron free for conduction. The resultant conductor is called n-type because the current carried by electrons is negative. Antimony having five outer electrons can serve this purpose. If an impurity, such as aluminium or gallium, having only three free electrons was used, there would be a shortage for pairing off with the four in the germanium crystal, and leave a hole. This type of semiconductor is called p-type because it has positive characteristics. Silicon can be rendered n-type or p-type in the same manner.
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