Journal of ELECTRONIC MATERIALS, Vol. 34, No. 6, 2005 Special Issue Paper 913 Current Voltage Modeling of Current Limiting Mechanisms in HgCdTe Focal Plane Array Photodetectors ANGELO SCOTTY GILMORE, 1,2 JAMES BANGS, 1 and AMANDA GERRISH 1 1.—Raytheon Vision Systems, Goleta, CA 93117. 2.—E-mail: angelo_s_gilmore@raytheon.com An automated iterative nonlinear fitting program has been developed to model current-voltage (I-V) data measured on HgCdTe infrared (IR) detector diodes. This model includes the ideal diode diffusion, generation-recombination, band- to-band tunneling, trap-assisted tunneling (TAT), and avalanche breakdown as potential current limiting mechanisms in an IR detector diode. The modeling presented herein allows one to easily distinguish, and more importantly to quantitatively compare, the amount of influence each current limiting mecha- nism has on various detectors’ I-V characteristics. Longer cutoff wavelength de- tectors often exhibit significant current limitations due to tunneling processes. The temperature dependence of these tunneling characteristics is thoroughly investigated for two diodes. Key words: HgCdTe, IV, modeling, trap-assisted tunneling (TAT) (Received October 7, 2004; accepted December 14, 2004) INTRODUCTION HgCdTe has acted as the primary source for in- frared detector materials for the past few decades due to its ideal tunable bandgap and relatively high operating temperatures. Current-voltage (I-V) char- acteristics are regularly used to quantify an infrared (IR) detector’s performance. The properties of a par- ticular IR detector’s I-V curve are dependent upon the dominant current limiting mechanism in the device. In turn, the current limiting mechanism de- pends upon several variables including the tempera- ture, applied bias, and cutoff wavelength or detector bandgap. In recent years, advancements in material growth and device processing have allowed longer cutoff wavelength detectors to become viable. One major limitation in these small bandgap devices is the leakage current arising from tunneling mechanisms at lower temperatures. Few methods exist to charac- terize these tunneling processes, and they are made further difficult due to the small bandgap inherent in long wavelength devices. In this paper, modeling is used to explore various current limiting mechanisms in infrared detector focal plane arrays (FPAs). Ideally, the only mechanism lim- iting the current would be diffusion of carriers. How- ever, in practice, a variety of different components are present that can act in opposition to the ideal diffusion current, potentially increasing the leakage current. The model presented here includes the ideal diode dif- fusion, generation-recombination, band-to-band tun- neling, trap-assisted tunneling (TAT), and avalanche breakdown as potential current limiting mechanisms in an IR detector diode. Each component has one or more variables that are fit during the course of the modeling. Detailed analysis of the TAT component provides some insight into this critical aspect of long wavelength detector performance. This model 1 is now routinely applied to Raytheon Vision Systems (RVS) detector test structures to better understand detector performance. MODEL Standard diode characterization methods include I-V measurements, which yield the familiar figures of merit R 0 A and I LK , the area-independent resistance at zero applied bias, and the leakage current evalu- ated at some nominal reverse bias value, respectively. An example of I-V curves for two diodes is shown in Fig. 1. In this figure, diode B is a very poor diode, while diode A shows much better electrical character- istics. These I-V measurements are often made as a function of temperature, providing R 0 A versus 1,000/T data, as shown in Fig. 2 for these same two diodes. There are three primary mechanisms that can