Hot point probe

A hot point probe is a method of determining quickly whether a semiconductor sample is n (negative) type or p (positive) type. A voltmeter or ammeter is attached to the sample, and a heat source, such as a soldering iron, is placed on one of the leads. The heat source will cause charge carriers (electrons in an n-type, electron holes in a p-type) to move away from the lead. The heat from the probe creates an increased number of higher energy carriers which then diffuse away from the contact point. This will cause a current/voltage difference. For example, if the heat source is placed on the positive lead of a voltmeter attached to an n-type semiconductor, a positive voltage reading will result as the area around the heat source/positive lead becomes positively charged.