The voltage required to produce this phenomenon, known as the avalanche voltage , varies greatly depending on the nature of the semiconductor material from which the device is fabricated. The avalanche voltage can range from a few volts up to several hundred volts. When an analog signal passes through a diode operating at or near its forward breakover point, the signal waveform is distorted. This nonlinearity allows for modulation, demodulation, and signal mixing. In addition, signals are generated at harmonics , or integral multiples of the input frequency .
Some diodes also have a characteristic that is imprecisely termed negative resistance .
Diodes of this type, with the application of a voltage at the correct level and the polarity, generate analog signals at microwave radio frequencies. These diodes are known as photovoltaic cells and are the basis for solar electric energy systems and photosensors. Yet another form of diode, commonly used in electronic and computer equipment, emits visible light or IR energy when current passes through it.