HgCdTe Diode Dark Current Modeling: Rule 07 Revisited for LW and VLW

Rule 07 is very convenient for dark current estimation of high-quality HgCdTe P-on-n photodiodes used in focal-plane arrays for science imaging, in which the diode behavior is dominated by the n-type absorption layer. Its popularity is partly due to the fact that it is very easy to use, while giving an accurate description of the evolution of the dark current with both temperature and cutoff. This modeling is actually the result of an empirical fit to experimental data from Teledyne Imaging Systems (TIS), short-wave infrared (SWIR) data between 300 K and 160 K, middle-wave infrared (MWIR) data around 80 K, and long-wave infrared (LWIR) data above liquid-nitrogen temperature (78 K). P-on-n diodes processed at CEA-LETI and SOFRADIR also follow this rule at high temperature and low cutoffs. However, at higher cutoffs (LWIR and very LWIR) and temperatures below 78 K, the measured dark current deviates from this rule. Indeed, in this wavelength range, the observed activation energy tends to be lower than the value given by Rule 07, closer to the semiconductor gap, which is more physically meaningful. This effect is also consistent with TIS data taken for the first characterizations of LWIR diodes for NEOCam at low temperatures. In this communication, the measured dataset is first presented and then discussed. Then, a new empirical rule describing the dark current of P-on-n HgCdTe diodes is proposed. This relation seems more suitable for this kind of wavelength and temperature (LWIR and VLWIR below 79 K) than the well-known Rule 07. Hence, Rule 07 represents a rough overestimation of the dark current for this range of wavelengths. The new expression should describe the low-temperature dark current in the LWIR and VLWIR regions more accurately.