<title>Effects of contact resistance on the performance of photovoltaic infrared detectors</title>

Abstract

ABSThAcT A simple diode model with a parallel photocurrent source is used to calculate the effects of detector series resistance on the electro-optical performance of infrared detectors. At low operating frequencies, where diode capacitance can be ignored, these calculations show that a saturation of the measurable short circuit current occurs. The flux levels at which this saturation occurs is dependent primarily on the series resistance and only logarithmically on detector junction impedance. The calculations also show that additional nonsaturated flux levels can be realized in the presence of a fixed series resistance by applying a reverse bias to the detector. At flux levels where low frequency signal saturation is not a problem, small series resistances can lead to premature rolloff of the frequency response. Calculations that consider the effects of detector capacitance and self biasing induced by the series resistance show an RC type time constant and frequency rolloff well before amplifier or intrinsic detector limitations. At higher flux levels, this rolloff is even more severe due to the bias dependent detector capacitance. A reverse bias can decrease the detector capacitance somewhat which can lead to a moderate increase in frequency response.

Bias dependence of photo-response in HgCdTe photodiodes due to series resistance

“…Although QE is supposed to be independent of bias [9], we have found that due to the presence of large series resistance, the effective QE also starts depending on bias voltage. Earlier reports on series resistance problem by Dhar [3] and Grenier [4] assume ideal diffusion limited current-voltage (I-V) characteristics model and hence could not predict the peaking behavior of the photoresponse with bias, as observed by us. In this paper, we have experimentally examined the effect of series resistance on the performance of medium wavelength infrared (MWIR) photodiodes of Hg 0.7 Cd 0.3 Te and found that for achieving highest possible QE in that particular photodiodes, there exists an optimum bias voltage.…”

“…To examine this effect let us consider the illuminated condition. The diode equation will be modified to the following relation with photocurrent (I Ph ) flowing through it [4,11].…”

“…(3)(4)(5), I 0 (x) represents that I 0 is a function of x. It is clear that I Ph cannot be extracted by simply subtracting the illuminated current and the dark current of Eqs.…”

“…Earlier Greiener et al did a detailed analysis of the performance of InSb photodiodes using a simple diode model and a parallel photocurrent source [4]. They have shown that the total available photocurrent, at low reverse bias, primarily depends on the series resistance and logarithmically on detector junction impedance.…”