PKOPEirnES OF lOXIC BOMBARDED SILICON lOo 



The present paper gives the I'esiilts of some more recent experiments 

 made with im|iro\e(l eciiiipment. Also descrihed biiefly are some related 

 experiments in which sihcon is boml)arded with alpha particles derived 

 from radioactive pt)lonium. The overall results of this work indicate 

 rather clearly that witli suitable variations of l)ombarding x'oltage, target 

 temperature and time of exposure as well as impiuit}^ content in the base 

 material, it is possible to pi'epare to specification silicon surfaces having 

 a wide range of properties. From the materials so treated it has l)een 

 possible to construct improved forms of signal rectifiers, harmonic gener- 

 ators, transistors, modulators, gating devices and also photo-electric 

 cells. It is particularly significant that the voltage range over which these 

 newer devices can be operated has been greatly extended, thus making 

 them useful in places not previously regarded as possible. Since these 

 new surfaces appear to be readily reproducible in large numbers and 

 since they are electricallj- tough, chemically stable and show no unsatis- 

 factory temperature or aging effects, it would appear that bombarding 

 technicjues should have considerable practical value. 



This paper is concerned mainly with the practical aspect of ion bom- 

 bardment of silicon, namely its effect on the voltage current character- 

 istics at low frequencies. Ef[ually important, perhaps, are its theoretical 

 aspects, particulai'ly with regard to the interpretation of the rather 

 pronounced changes in the properties in light of presently-accepted views 

 of solid-state physics. These aspects are not covered in this paper. 



METHOD 



The bombardment process referred to above consists of exposing the 

 silicon surface to ions that have previously been accelerated to energies 

 in the range from about 100 electron volts to about 30 kilo-electron-volts. 

 A recent setup is illustrated in Fig. 1. The electrons from a tungsten 

 cathode are accelerated toward a grid which is at a positi\'e potential with 

 respect to the cathode. Many of the electrons pass a short distance 

 beyond the grid and return for ultimate capture. Ionization due mainly 

 to the impacts of electrons with gas molecules takes place in this turn- 

 around region, producing amongst other things positive particles. Elec- 

 trodes are so proportioned that this ionization is fairly uniform over the 

 grid area. 



The silicon specimen to be bombarded is made negative with respect 

 to the filament. This accelerates the positively charged particles toward 

 the target. The latter rests on a graphite plate heated by a coil below, 

 carrying high-frecjuency currents. A thermocouple with suitable con- 

 nections to the exterior makes possible an adefjuate measurement of 



