| 摘要 |
925,397. Semi-conductor devices. SIEMENS & HALSKE A.G. June 22, 1959 [June 25, 1958], No. 21314/59. Class 37. In a semi-conductor breakdown device comprising a PNPN zone configuration a resistive path including a PP+ junction is used to shunt the outer junction 1, as shown in Fig. 4, or junction 3 is shorted by a resistive path including an NN+ junction to zone III. The device shown in Fig. 3 and its NPNN+ equivalent, which are said to be electrical equivalents of these arrangements, are also possible. In the Fig. 3 device the outer N zone is replaced by a P+ zone including both donor and acceptor impurities, the donor concentration being greater than the acceptor concentration in the adjacent zone. In the Fig. 4 arrangement the resistive path shunts junction 1 and this functions to reduce the effective amplification factorαof zones I, II, III and thus of the device as a whole. With increasing bias the forward resistance of junction 1 falls to render the shunt less effective so that ultimately a, which increases with current across the junction rises to make the overallαexceed 1 and the device becomes conductive. The voltage at which breakdown occurs is determined by the total resistance of the shunt path which may include a resistor R. If junction 3 has a low Zener breakdown voltage the device is conductive with the bias reversed because of the shunt. The resistor may be replaced by a rectifier or by a resistor sensitive to light, heat or magnetic field to provide switching in response to changes in these conditions. In the alternative device, Fig. 3, control over the breakdown voltage may be provided by a variable resistor R shunting junction 3. By virtue of the reverse conductivity both arrangements may be switched to the breakdown condition using a voltage less than the normal forward breakdown voltage by a momentary reversal of the applied voltage. During the reversal the body becomes swamped with minority carriers which momentarily lower the forward breakdown voltage. A PNPP+ device of the Fig. 4 type may be formed from an 8-10 ohm cm. P-type germanium disc by the steps of diffusing arsenic into its entire surface to form an N-type layer, etching in CP4, masking a circular area on one face and then etching to remove the N-type layer from the rest of the wafer, alloying a ball of 98% indium, 2% arsenic (by weight) to the opposite face of the wafer and finally vacuum depositing aluminium on the formerly masked area and alloying it thereto. |
