Electrical and optical performance investigation of si-based ultrashallow-junction p ⁺-n VUV/EUV photodiodes

Recently, a silicon-based ultrashallow-junction p ⁺-n photodiode (B-layer diode) has been reported, with very high and very stable sensitivity in the vacuum-ultraviolet and extreme-ultraviolet spectral ranges. However, the ultrashallow nature of the junction leads to a high series resistance of the photodiode if no conductive capping layers are used. In a recent paper by Shi , a study on the relation between the sensitivity and the series resistance of the B-layer diodes, which can be large due to the shallow-junction depth, was presented. In this paper, an extensive analysis of the photodiode electrical and optical performance parameters and their interrelation is given. The influence of the series resistance on the response time of the photodiode for different illumination patterns is studied theoretically and also experimentally verified. It has been proven by modeling, simulations, and experiments that the time constant of the photodiode does not change significantly with the illumination spot area. This effect is due to temporary variations, going in opposite directions, of the equivalent series resistance, and the junction capacitance values found at the first instant a photogenerated charge are locally stored in the photodiode p-n junction. Also, the dependence of the degradation of the sensitivity on the incident wavelength and the diode vertical stack is examined through analysis and experimentation.