Differences of silicon photodiode spectral reflectance among the same batch

Abstract

Photodiode's reflectance plays an important role regarding the relation between responsivity and the incident flux. In this work we analyze how the spectral reflectance changes among photodiodes from the same manufacturer and batch and how the reflectance of three standard photodiodes has drifted during six years. The results show that the reflectance changes from diode to diode within the same batch and also show that the reflectance of photodiodes changes on time. This ageing is spectrally dependent.Silicon photodiodes are more sensitive and quicker than thermal detectors. For these reasons silicon photodiodes are used to maintain scales of spectral responsivity in the spectral range (300 nm -1000 nm) in many National Laboratories [1][2][3][4][5] .The spectral responsivity of a photodiode depends on the reflectance and the internal quantum efficiency, so a good approach to determine responsivity is to know both reflectance and internal quantum efficiency. Because of that, in this work we present a study about the reflectance of silicon photodiodes, with two goals: to study the variability of reflectance among photodiodes from a single batch, and to study the reflectance aging of some silicon photodiodes used as standards during six years. In some radiometric applications, the reflectance of individual photodiodes plays an important role because they have to match to a pair or be minimized or maximized, as it is the case for silicon trap radiometers [6,7] . The ageing of silicon photodiodes has been studied by several authors and all of them looked at the stability of the internal quantum efficiency [8,9] rather than at the reflectance.

Photodiodes as Optical Radiation Measurement Standards

“…The same results are depicted for the photodiodes 2 and 5, manufactured by a second company. It is important that the results do not depend on the polarization state of the incident light when the angle of incidence is smaller than 10 degrees [22]. …”