Patent GB-1139767-A (GB)
Title: Improvements in or relating to activesolid-state circuit elements
IPC: G02F1/355
Filed: 1966-04-22
Abstract: 1,139,767. Semi-conductor devices. SIEMENS A. G. 22 April, 1966 [23 April, 1965], No. 17619/66. Heading H1K. Microwave or I.R. radiation (101<SP>10</SP> to 10<SP>13</SP> Hz) is generated or amplified by means of the interaction of electromagnetic (EM) waves with electrons exhibiting a negative effective mass. The electrons are injected into a semi-conductor dielectric medium, in which the interaction occurs, from a layer having a degenerate electron concentration, the electrons being energized by the harmonics produced in an optically non-linear medium from an incident laser beam of fundamental frequency. As shown, Fig. 2, an oscillator comprises an optically non-linear medium 21, a layer 22 of a metal having a degenerate electron concentration, e.g. a precious metal, a semi-conductor dielectric layer 23, an electrode 24, 25 and a medium 26, in which the output radiation is propagated separated from layer 23 by a semiopaque window 27. A laser beam of frequency #F is incident on non-linear medium 21 at such an angle that a preferred harmonic, e.g. 2 #F , enters metal layer 22 with maximum intensity. Electrons in layer 22 are excited to such a level that on entering semi-conductor dielectric layer 23 they enter the upper part of the conduction band where they exhibit a longitudinal negative effective mass. The electrons move through layer 23 under the influence of a voltage applied between electrode 24, 25 and metal layer 22. The initial electron injection generates EM radiation, the desired frequency being selected by the construction of layer 23 as a Fabry-Perot resonator. The electric vector of the radiation interacts with the negative effecttive mass electrons which move in the direction against the force and impart energy to the wave. The semi-conductor dielectric is arranged so that the high energy electrons drift in the direction of the highest electron energy minima of the lattice, and the dielectric may be subjected to shear or compressive stresses to raise or lower anisotropically the energy minima of the material to achieve a directional selection of the high energy electrons. A static magnetic field may be applied to the semi-conductor dielectric causing the high energy electrons to move in helical paths to lengthen their trajectories and hence the duration of their interaction with the EM radiation. As shown, Fig. 3, an amplifier may be produced by placing a second optically non-linear layer 28 on the output side of layer 23, which in this case does not form a resonator. Signal input radiation of frequency # S , produced by heterodyning laser beams of frequencies # 1  and # 2  in layer 28, enters layer 23, where it is amplified by interaction with negative effect mass electrons injection from layer 2, is reflected by layer 22 and leaves the device via layer 28. An alternative form of amplifier is shown in Fig. 4, the semi-conductor dielectric layer 34 being provided with an electrode 33 which together with metal layer 32 forms a resonator. A thin insulating layer may be inserted between the metal layer in which the high energy electrons are generated and the semi-conductor dielectric layer. The electrons tunnel through this insulating layer and, since a large proportion of the voltage applied between the metal layer and the electrode of the semi-conductor dielectric layer is dropped across the insulating layer, suffer a large drop in potential and hence gain in kinetic energy. The insulating layer allows the energy diagram of the semiconductor dielectric layer to be shifted arbitrarily relative to that of the metal layer, the amount of the shift being controllable by means of the bias voltage. Amplifiers using such a dielectric layer are described with reference to Figs. 6 and 7 (not shown). The optically non-linear medium may be a ferro-electric material such as guanidine aluminium sulphate hexahydrate or triglycine sulphate and may also comprise an An B vI  or A III  B v  compound or a ZnS/CdS or CdS/CdSe alloy. The semi-conductor dielectric may be an N-type A III  B v  - flawless crystal and may comprise an epitaxial layer or a plurality of layers of different composition or doping, and the following semi-conductor materials are mentioned: Si, AlP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs, InSb. P-type A III  B v  compounds may also be used. The insulating layer. if present, between the metal and the semiconductor dielectric may comprise an oxide of either of these materials. The laser may be formed as part of the device and may comprise a PN junction. The layer of degenerate electron concentration may be a semi-conductor material doped to degeneracy instead of a precious metal. The device may be cooled to reduce interactions between the high energy electrons and the lattice oscillations. Formulae are given expressing design considerations for the device. The devices may be produced by conventional thin-film techniques. The output signal may be modulated either by modulating the laser beam which generates the high energy electrons or by applying low frequency A.C. signals between the metal layer and the electrode on the semi-conductor dielectric layer.