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Abstract

A semiconductor device with a tunnel diode (23) is particularly suitable for various applications. Such a device comprises two mutually adjoining semiconductor regions (2, 3) of opposed conductivity types and having doping concentrations which are so high that breakdown between them leads to conduction by means of tunnelling. A disadvantage of the known device is that the current-voltage characteristic is not yet steep enough for some applications. In a device according to the invention, the portions (2A, 3A) of the semiconductor regions (2, 3) adjoining the junction (23) comprise a mixed crystal of silicon and germanium. It is surprisingly found that the doping concentration of both phosphorus and boron are substantially increased, given the same amount of dopants being offered as during the formation of the remainder of the regions (2, 3). The tunnelling efficiency is substantially improved as a result of this, and also because of the reduced bandgap of said portions (2A, 3A), and the device according to the invention has a much steeper current-voltage characteristic both in the forward and in the reverse direction. This opens perspectives for inter alia an attractive application where the tunnelling pn junction (23) is used as a transition between two conventional diodes, for example pn or pin diodes, which are used one stacked on the other and which can be formed in a single epitaxial growing process thanks to the invention. The portions (2A, 3A) adjoining the tunnelling junction (22) are preferably 5 to 30 nm thick and comprise between 10 and 50 at % germanium. The doping concentration may be 6.times.10.sup.19 or even more than 10.sup.20 at/cm.sup.3. The invention further relates to a simple method of manufacturing a device according to the invention. This is preferably done at a temperature of between 550.degree. C. and 800.degree. C.

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First Claim