Experimental studies on a silicon photodiode have been carried out to achieve the performance characteristics required for applications such as spectroscopic measurements. Sheet resistance was applied as a control parameter for diffusion to obtain a shallow junction less than 1 μm in depth. For high ultraviolet responsivity, the diffusion layer, in which a built-in field is induced by the impurity gradient, was optimized for values of the sheet resistance of about 800-2000 O/μ. The device responded in the wavelength range of 200-1000 nm,and had a responsivity of 0.065 A/W at 200 nm. In order to reduce influence of stray light in spectroscopic measurements, two types of photodiodes were fabricated with photoresponse reduced in the long-wavelength portion. A p+-n-p+ device was found preferable to a p+-n-n+ device. And the device structure with an extended electrode was desirable for high, reliable performance. Copyright © 1979 by The Institute of Electrical and Electronics Engineers, Inc.