PEOPERTIES OF lOMC liOMBAUDEU SILICON 117 



KFFECT OF MATERIAL COMPOSITION 



^Tlius far discussions have ('(Mit(M-(Hl around a sinj>;lc type of high purity 

 material that was I'egai'ded as repr(\s('iitative. It is of iiit(M'est to exuiniue 

 tiie etfect on otluM' inat(M'ials particuiaily those in which impurities have 

 been added. For this ])urj)ose tests were made on compai'ahle samples 

 from four sources all bombarded foi- two minutes with o microamperes 

 of current and each with li\e r(>pres(>ntati\'e bombardinji; Noltages. The 

 results are illustrated by the curves shown in V'lg. <S. llie four columns 

 correspond to j)r()gi-essively hif>;her percentajijes of imjiuritics beginning 

 with (a) on the left as a material ha\ing an impurity content believed 

 to ))e less than 0.01 per cent. The impurity content of (b) is not known 

 accurately except that it lies between (a) and (c). The material repre- 

 sented l\y column (c) was protluced by adding 0.02 per cent boron** to 

 a material illustrated in column (a). The last column (d) was produced 

 by adding 0.1 per cent boron to the material illustrated in column (b). 

 It is to be noted from Fig. 8 that marked changes in the voltage- 

 current characteristic may be effected by l)oml)ardment for all degrees 

 of the impurity content shown. It is especially interesting that in columns 

 (c) and (d) corresponding to materials contaminated with boron to the 

 point where nonlinearity is almost absent, rectification can not only 

 be restored but indeed the product may be made better than the best 

 imbombarded material . 



EFFECTS OF ALPHA-PARTICLE BOMBARDMENT 



The close relationship between helium ions such as generated above 

 and alpha particles such as emanate from radioactive materials suggests 

 that the latter may be used for the bombardment of silicon surfaces. 

 A few experiments of this kind have been made with results that are 

 not only interesting l)ut possibly useful. For these tests, four sources of 

 alpha particles were obtained. They consisted of fV i'^fli scjuare pieces 

 of nickel on which had been plated a thin coating of polonium followed 

 by a covering of gold. The initial strength was 4 milliciu-ies per square 

 centimeter. The half-life of polonium is 140 days. 



The process of liombardment consisted simply of placing the polished 

 surface of a standard silicon scjuare against the layer of gold and examin- 

 ing the same periodically. Tests of four samples were carried out simul- 

 taneously. The results are given in Table II. The data for Sample No. 1 

 departs so markedly fi'om the mean that it may l)e disregarded. Since 



^ Boron is a particularly active a^ont in etlcctitig ctiaiigos in the properties 

 of silicon. 



