PHOTOKLKl "rUIC I'UOl'KUriKS OF lOXICAhLV B( )MHA KDIOD SILICON 811 



range previously mentioned. The peak of the lowest voltage cell is 

 definitely toward the blue compared with the other five whose maximum 

 is constant at about 0.725 /x- 



One objective in this studj^ was to obtain evidence relating to the 

 depth of the barrier below the silicon surface as a function of the energy 

 of the bombarding particles. The higher the velocity of the particles the 

 further beneath the surface one would expect the barrier to be located 

 and as a r(\sult there might be a shift in the spectral characteristic toward 

 the red with increasing depth of the barrier due to the relatively greater 

 absorption at the blue end. There is however, a selective or secondary 

 maximum at the jjeak which sharpens it and imllifies the effect of the 

 warping of the entire curve. The blue to red shift can be shown as in 

 Fig. 9 by plotting the ratio of the responses in Fig. 8 at 0.50 n and 1.0 /x. 

 Thus at low voltage the blue to red ratio is high and decreases as the 

 l)ombarding potential is raised. 



In the spectral curves it will be noted that there are a number of 

 secondary humps located near the top of the curves and extending down 

 on the blue side. There is a strong tendency for them to occur at definite 

 wavelengths and to be evenly spaced regardless of the bombarding voltage. 



SPECTRAL MEASUREMENTS ON THE LARGE CELLS AND TH^ EFFECT OF 

 MATERIAL COMPOSITION 



For the large cells, two grades of silicon were used both prepared by 

 pyrolytic reduction of SiCU and called "hyper-pure". These will be 



2.8 



0.8 



0.8 



1.6 



4.0 



4.8 



2.4 3.2 



LOGio -VOLTS 



Fig. 9 — Ratio of blue to near infra-red response versus bombarding voltage. 



