Field‐Effect Light Modulation in Germanium

摘要

Infrared light that is sent through a germanium prismatoid so that it is reflected several times internally, becomes modulated in intensity if the space‐charge layers along the reflecting surfaces are changed by means of the field effect. The phase angle between the modulation signal and the field voltage changes by π when the surface is changed from n to p type, or vice versa, by change of the gaseous ambient. The modulation signal shows twice the frequency of the field voltage in the transition region between n and p type. This, together with other observations such as the waveform analysis of the modulation signal and the dependence of the modulation depth upon field voltage, indicates that the modulation is caused by free‐carrier absorption in the space‐charge layer, which follows roughly the master curve of the field‐effect surface conductivity. The results are interpreted in terms of the field‐effect mobility.