Response Speed In Semiconductors
In this article, the topic of discussion is response speed in semiconductors. As we know that the fundamental speed of semiconductor detectors is dependent upon the transport of electrons through the semiconductor bands.
There are some materials in which the speed of electrons is greater than others. For example, the substance like germanium and gallium arsenide possess greater electron mobility’s as compared to that of silicon. Hence they are given preference over other semiconductor materials to be used in high frequency applications. Read on to know more on response speed in semiconductors.
The high response speed of semiconductors materials is affected by the semiconductor plasma frequency. There are detectors which are known as metal-insulator detectors having double insulator operating at very high frequencies due to higher plasma frequencies in metals and ultra-short tunneling times through the diode. Considering the terminology used in the field of radio waves, the plasma frequencies of semiconductors are known as carrier frequencies.
The RC time constant which is dependent upon the device area, materials used to manufacture devices, the thicknesses of device and the lead dimensions ultimately limits the signal to terahertz frequencies. A test for the response speed of semiconductors was conducted on a metal-insulator detectors at 200 GHz by mixing two high frequency signals together to obtain the difference frequency. By identifying the difference signal we could be sure that we were not detecting a thermal response of the diode, however that the diode was in fact rectifying at the high frequency. Just to mention here, the measurements were carried out using two approximately 200 GHz sources in a Harvard-Smithsonian laboratory. The final results were agreed with what was calculated based upon the low-frequency current-voltage characteristic of the device.
The above said experiment was also authenticated at semiconductors response speed 1 THz. To circumvent the RC-time limit, the company which carried out the above experiment has patent-pending traveling wave detector structures.