Dependence of photodiode spectral sensitivity on temperature

Abstract

The development of optical control methods has led to the construction of devices in which the basic elements are photosensitive detectors. The illumination of these elements is necessary for the operation of devices with normalizable characteristics. Some of the most widely used photodetectors are silicon-or germanium-based photodiodes.One of the least studied, and very often least considered, parameters of photodiodes is the temperature dependence of their spectral sensitivity. Published data for silicon photodiodes is often contradictory [i], and for germanium, available only near the band edge [2]. This situation is apparently due to the experimental difficulties encountered in the various studies.Below we examine the temperature dependence of silicon and germanium photodiodes. For the investigation, photodiodes fabricated by a number of different technologies, presented in Table I, are used.The relative spectral sensitivities of the photodiodes were measured on a spectral instrument described in [3]. The calibration of the spectral sensitivities is accomplished with a standard light source based on a light-emitting diode [4]. Measurements were made over a temperature range of 15-30~A precision thermal regulator, described in [5], was employed.The measured absolute spectral sensitivity S[A/W] and the temperature coefficient of the spectral sensitivity 6[%/](] for silicon and germanium photodiodes are shown in Figs. (i) and (2), respectively. It is possible to present the data in this form because in the temperature range of interest, the parameter ~ is a constant at any wavelength.All results presented are for the photovoltaic regime with an external measuring circuit with load resistance much less than the intrinsic resistance of the photodiodes.For the most part, one can extract some general rules from the data. For the peak sensitivity wavelength lmax, corresponding to the maximum sensitivity, all photodiodes have a value of $ > 0. This is related to the we11-known temperature dependenceof the forbidden transition region band, and the corresponding shift in the absorption edge. For ~ > %max the value of ~ rises. This can also be explained by the temperature dependence of the diffusion length of the minority carriers which, diffusing from the collector region, reach the p-n junction. For ~ < lmax, useful general rules are not found. We examine the results in this spectral region for a few silicon photodiodes (see Fig. i).In the range from %max to the visible there is a decrease in the temperature coefficient into the short wavelength region where its sign eventually changes from positive to negative. This is associated with the temperature dependence of the absorption coefficient in the base. From the value of ~ in this spectral region it is possible to estimate the photodiode thickness. The less the absolute value of 8, the thinner the base of the photodiode. Accordingly, the base thickness ranges from a fraction of a micron for PD288K to 40 microns for PDI42K.In the near ultraviolet spectral region, the a...

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