The P and N regions of PN junction are connected with a lead, and then packaged into a semiconductor diode. The lead connected with P region is positive, and the lead connected with N region is negative.
Detector diodes are fabricated from staggered semiconductor materials, using a point-contact diode structure, as shown in Figure 14-4. Because of the point contact structure, its contact area is small and can not pass through large current, but its junction capacitance is small and its frequency characteristic is good, so it is suitable for high frequency signal detection.
Detector diodes are widely used in radio, television, recorder and communication equipment. The detection of detector diode is usually for high frequency and small signal, so it is based on the single conductive characteristics of the diode.
Fig. 14-5 shows the relationship between the voltage and current of the detector diode (stagger diode), also known as the volt-ampere characteristic curve. When a positive voltage is applied to both ends of the diode, a positive current is generated. When the forward voltage is small, the resistance of the diode is larger. When the forward voltage exceeds a certain value, the resistance of the diode becomes very small and the current rises sharply. The initial turn-on voltage of the anchor diode is about 0.2V. When the reverse voltage is applied to the diode, there is only a small reverse current, and the current does not change with the increase of the reverse voltage. In this case, the current is called reverse saturated current. When the reverse voltage force is applied to a certain value, the reverse current will suddenly increase and breakdown will occur.