Germanium PME fast response light detector

If the geometrical thickness w of a semiconductor is smaller than the diffusion length of its carriers, the response time of its photomagnetoelectric (PME) effect becomes dependent on w, decreasing with decreasing w, while at the same time its voltage sensitivity increases. A germanium device, e.g., in which the sample is placed between the poles of a small permanent magnet produces output voltages of 200 mw with response times of well below 1 µsec at high light intensities. The thin Ge wafers used in this device were obtained by controlled photoetching of single crystals to a thickness of 6 microns whereby the current leads for the etching are arranged in such a way that they serve later as PME leads. The characteristics of the cell are presented in detail and show a voltage sentry almost independent of the light wavelength from the visible to up to 1.9 microns as well as its dependence on the incident light intensity and the temperature. Since the device does not contain junctions, only thermal noise is expected. Preliminary tests with PME cells which are photovoltaic and therefore do not need any power supply reproduced 1 µsec light flashes, and also the fine structure of ruby Laser signals with the same resolution as photomultiplier tubes.