Radiation sensitive semiconductor device for optical reading or writing

Abstract

A radiation-sensitive semiconductor device comprises a semiconductor body having a first semiconductor region of a first conductivity type, which adjoins with one side a surface of the semiconductor body and adjoins within it at a certain distance from and substantially parallel to the surface a second semiconductor region of a second conductivity type opposite to the first type and forms with it a first pn junction. Such semiconductor devices are used in a reading or writing unit for a system for optical recording, such as CD, LV, DOR and CDV. In one embodiment having a semiconductor region at least two further regions are present, which are located at the surface and each form with the first semiconductor region a further pn junction substantially parallel to the surface and at a smaller distance therefrom than the first pn junction. Moreover, the further regions, like the first semiconductor region, are coupled to reading members, by means of which a current can be measured. As a result, the further semiconductor regions can be thin and can therefore be arranged close to each other so that a focus error signal without a dip is obtained via the reading members coupled to these regions. Since the further regions result in diodes having an inverse polarity, class B amplifiers based on npn transistors may now be integrated in with the semiconductor device so that a separation circuit requiring comparatively large capacitances is no longer necessary.