Patent GB-750134-A (GB)
Title: Improvements in or relating to semi-conductor devices
Filed: 1952-07-11
Abstract: 750,134. Semi-conductor devices. SIEMENSSCHUCKERTWERKE AKT.-GES. July 11, 1952 [July 12, 1951], No. 17597/52. Class 37. [Also in Group XL (c)] An amplifier device comprises an intrinsic semi-conductor body which is subjected to perpendicular magnetic and electric fields so that electron-hole pairs are displaced towards one surface of the body, thereby forming crowded and depleted carrier regions, at least one surface of the body having a low effective recombination rate so that the average carrier density of the body is varied, whereby a change in the magnetic or electric field produces a change in the resistance of the body. Fig. 4 shows an amplifier arrangement in which a bar of intrinsic semi-conductor 10 having low resistance ohmic contact electrodes 17 and 18 is placed between the poles of an electromagnet 11. An electric field is produced between electrodes 17 and 18 by means of battery 15. If the magnetic field is varied by signals from source 14, amplified signals appear in the load 16 connected in series with electrodes 17 and 18, due to changes in the resistance of the semi-conductor 10. The change in the electric field produced by the change in resistance between electrodes 17 and 18, also reacts on the semi-conductor, so that the device possesses inherent positive feedback. The variable resistance effect is increased if one side face of the semi-conductor is subjected to electrolysis or etching treatment, and the opposite face is ground and polished. When provided with these different surface treatments, the device is asymmetrical and if the magnetic field is maintained constant, it operates as a rectifier having electrodes 17 and 18. In Fig. 6, a constant magnetic field perpendicular to the plane of illustration is provided by permanent magnet 34. An alternating current source 35 and control means 36 supplies an input signal, to vary the electric field between electrodes 31 and 32, which varies the effective resistance of the semi-conductor 30 and results in amplified current variations between electrode 31 and an additional ohmic contact electrode 33. The magnetic field may also be varied to provide an arrangement having two controlling inputs. Additional electrodes similar to electrode 33 may be provided. Theory of operation.-Under the influence of the magnetic and electric fields, both the electrons and holes in the semi-conductor are deflected to the same side of the body, producing regions of high and low carrier densities relative to that which normally exists throughout the intrinsic material. Thermo-generation of electron-hole pairs tends to reduce the deficit of carriers on the depleted side, while electronhole recombination tends to reduce the excess on the crowded side. Under equilibrium conditions the carrier density in each region remains constant. Since both holes and electrons are displaced together, no space charge is produced (unlike the usual Hall effect device) and equlibrium is established when the effect of the magnetic forces is balanced by electron and hole diffusion. Surface effects are more important, and electron-hole pairs are generated at a rate Sn i , where S equals the surface recombination constant and n i  the electron concentration in the intrinsic material, while surface recombination takes place at a rate Sn, where n is the actual electron concentration at the surface region concerned. Thus there is a net generation of carriers on the depleted side, and a net recombination on the crowded side. The depleted side or low density region is termed the magnetic barrier layer, which has high resistance. It is stated that if the surface recombination constant S is low enough, the arrangement is such that the total number of carriers, and therefore the average carrier density is changed to modify the resistance of the semi-conductor body. The depth of the high resistance magnetic barrier layer may be increased by surface treatment of the semiconductor to reduce the surface constant S on the depleted side, and to increase this constant on the crowded side. The surface constant may be increased by grinding and polishing the surface, or reduced by anodic treatment in an electrolytic bath or for example, by etching germanium with a solution of caustic soda and hydrogen peroxide. Silicon, germanium, grey tin, indium antimonide, gallium antimonide, aluminium antimonide, indium arsenide, gallium arsenide, lead sulphide and other materials described in Specification 719,873 may be used as the semi-conductor body. The magnetic barrier ' layer may be several centimetres thick, thus enabling large currents (1 amp.) and voltages (1000 v.) to be handled. The device may be used for detecting, amplifying, regulating or switching operations.