Patent GB-990345-A (GB)
Title: Electromagnetic wave amplifier
IPC: H01S5/32
Filed: 1963-05-03
Abstract: 990,345. Masers. STANDARD TELEPHONES & CABLES Ltd. May 3, 1963, No. 17539/63. Heading H3B. [Also in Divivision H1] An amplifier for infra-red or microwave frequencies comprises a tunnel diode formed from a semi-conductor material having an abnormal (-) g factor, which is doped with ptype material having a normal (+) g factor, the diode being back biased by a D.C. potential and located at low temperture in a magnetic field. Tunnel diode. A p+n diode 1, Fig. 3 (not shown) and Fig. 5, consists of a monocrystalline semi-conductor body having an abnormal (-) g factor for conduction electrons which is formed with an abrupt junction 5 between lightly n-doped and heavily p-doped regions 3, 2. Connections from a back-biasing D.C. supply 4 are made to electrodes 13, 14 fused to the exposed ends of regions 2 and 3 respectively. The D.C. voltage is sufficient to enable valence electrons to tunnel from the p+ region 2 to the conduction band of the n region 3. Suitable semi-conductor materials are stated to be indium antimonide, indium arsenide and gallium arsenide heavily doped with a p-conductivity type and +g factor impurity such as indium, gallium or zinc on one side of the junction, and lightly doped with an n-conductivity type impurity such as antimony, phosphorus or tellurium on the other side of the junction. Operation. The tunnel diode is maintained at a thermal equilibrium temperature in a dewar vessel 6, and a magnetic field from polepieces 12 is used to separate the valence electrons of region 2 and the conduction electrons of region 3 into Zeeman sub levels. Fig. 4 shows an energy level diagram for an indium antimonide diode (g = - 58) heavily doped in region 2 with a p-type impurity (g = + 2), the magnetic field separating the valence and conduction electrons in regions 2 and 3 respectively into energy bands 25, 26 and 23, 24. The upper levels are less populated than the lower levels, and since the g factors of the two regions are respectively normal and abnormal the electrons having spins parallel with other applied magnetic field occupy levels 25 and 24, and the electrons with antiparallel spins occupy levels 26, 23. When the D.C. bias voltage is applied, the tunnelling valence electrons move into the energy levels in region 3 corresponding to their direction of spin, and as shown in the Figure, this effect causes an inversion of population density in region 3. Stimulated emission takes place when region 3 is irradiated by an electromagnetic wave (in this case in the infrared range) having a frequency equal to the energy level gap #3. A modification for amplifying microwave frequencies is described, Fig. 6, in which a gallium arsenide diode is doped with p conductivity type material having a g factor of + 2, the g factor of gallium arsenide being - 1À6. In this case the energy gap #3 of region 3 is less than that of region 2. Infra-red amplifier. As shown in Fig. 5, the dewar vessel comprises an evacuated region 7 and a region 10 containing a coolant. In Fig. 3 (not shown), windows are provided in the dewar vessel for the incident and emergent infra-red electromagnetic waves, the windows being aligned with region 3 of the tunnel diode 1. A tuned cavity is provided by the metallic wall of electrode 14 and the metallic-like properties of region 2. Microwave amplifier. The tunnel diode is located in a metallic resonant cavity 29, Fig. 5, which is positioned in a dewar vessel and is connected to a circulator 31 by a waveguide 28, a microwave source 30 and an output detector 32 being coupled to the circulator. Specification 986,589 is referred to.