Elektronenquelle mit einem Halbleiterkoerper

摘要

1275972 Cathode materials and processing RCA CORPORATION 4 Aug 1969 [12 Aug 1968] 38929/69 Heading H1D A negative effective electron affinity electron emitter comprises a P-type semi-conductor body 4 having a given energy gap and including a deep acceptor impurity and a layer 5 a few atomic diameters in thickness of an electropositive work function reducing material on a given surface of the body 4, wherein the ionization energy of the deep acceptor, preferably greater than 0À1 ev., does not exceed the difference between the given energy gap and the work function of the layer 5. Further, either a thin P+ type surface region 3 or a non-injecting Schottky barrier formed by a high work function material is formed on the face of the semiconductor opposite that on which layer 5 is formed to prevent electrons from diffusing away from layer 5. An arrangement, independent of P+ type region 3 or the Schottky barrier, is provided to bombard the emitter with electrons to excite electrons into the conduction band of the semi-conductor. Emission is thus facilitated since the vacuum energy level at the surface of the emitter, Fig. 2 (not shown), lies below the bottom of the conduction band in the bulk of the semi-conductor body 4 such that an effective negative electron affinity exists at this surface enabling conduction band electrons diffusing to the surface to arrive thereat with sufficient energy to be emitted therefrom. Also, because of sloping of the bands, an internal potential gradient is formed in the semiconductor which impels electrons toward the emitting surface. The semi-conductor body may comprise gallium phosphide and the deep acceptor impurity may be iron, chromium or copper. The work function reducing layer 5 may comprise caesium or caesium and oxygen and the thin P+ type region 3 formed by a shallow acceptor such as zinc, cadmium or beryllium. As shown, the semi-conductor body is formed with an alumina substrate 2 adjacent to and supporting the P+ type region 3, and if this substrate 2 is sufficiently thin, e.g. 500 Š or less, and the incident electron energies sufficiently high, e.g. 3000 ev., the emitter may form a transmission type dynode. A polycrystalline (or monocrystalline) gallium phosphide layer 4 doped with iron to a concentration of 1017-1018 atoms/cm.3, may be deposited on to a beryllium layer 3 by the vapour phase reaction of gallium chloride, ferrous chloride and phosphine at 800‹ C. During the growth of this layer the beryllium diffuses into a short distance, e.g. 10- 100 Š, into the gallium phosphide to form the P+ type region. Preferred layer thickness and dopant concentrations are given. Platinum may comprise the high work function metal that is used to provide the Schottky barrier.