Theory of multiple-stage interband photovoltaic devices and ultimate performance limit comparison of multiple-stage and single-stage interband infrared detectors

Abstract

A theoretical framework for studying signal and noise in multiple-stage interband infrared photovoltaic devices is presented. The theory flows from a general picture of electrons transitioning between thermalized reservoirs. Making the assumption of bulk-like absorbers, we show how the standard semiconductor transport and recombination equations can be extended to the case of multiple-stage devices. The electronic noise arising from thermal fluctuations in the transition rates between reservoirs is derived using the Shockley-Ramo and Wiener-Khinchin theorems. This provides a unified noise treatment accounting for both the Johnson and shot noise. Using a Green's function formalism, we derive consistent analytic expressions for the quantum efficiency and thermal noise in terms of the design parameters and macroscopic material properties of the absorber. The theory is then used to quantify the potential performance improvement from the use of multiple stages. We show that multiple-stage detectors can achieve higher sensitivities for applications requiring a fast temporal response. This is shown by deriving an expression for the optimal number of stages in terms of the absorption coefficient and absorber thicknesses for a multiple-stage detector with short absorbers. The multiple-stage architecture may also be useful for improving the sensitivity of high operating temperature detectors in situations where the quantum efficiency is limited by a short diffusion length. The potential sensitivity improvement offered by a multiple-stage architecture can be judged from the product of the absorption coefficient, α, and diffusion length, Ln, of the absorber material. For detector designs where the absorber lengths in each of the stages are equal, the multiple-stage architecture offers the potential for significant detectivity improvement when αLn ≤ 0.2. We also explore the potential of multiple-stage detectors with photocurrent-matched absorbers. In this architecture, the absorbers are designed to absorb and collect an equal number of carriers in each stage. It is shown that for zero-bias operation, this design has a higher ultimate detectivity than a single-absorber device. Such improvements in detectivity are significant for material with αLn ≤ 0.5. Using the results derived for general values of αLn, we offer an outlook for multiple-stage detectors that utilize InAs/GaSb superlattice absorbers.

Interband cascade infrared photodetectors with long and very-long cutoff wavelengths

“…This is expected based on the theory for an ideal diffusion-limited detector. However, the dark current data for some two-and threestage devices, especially at low temperatures, did not follow what was expected from theoretical predictions [8,11]. This was likely due to variations in material uniformity and device fabrication.…”

“…In addition, the photo-response of these detectors was strongly dependent on bias, indicating that further research and device optimization are necessary. Two-stage ICIPs in the long-wavelength infrared (LWIR) spectrum (8)(9)(10)(11)(12) lm) were able to operate at higher temperatures (up to 250 K) with an extended cutoff wavelength of $12 lm. At 78 K, these LWIR detectors had a bias-independent photocurrent, with an R 0 A of 115 X cm 2 .…”

“…Theoretical calculations [1,2] and experimental results [3,4] indicate that type-II InAs/Ga(In)Sb superlattice (SL) photodetectors are a promising alternative to mercury cadmium telluride (MCT) detectors, especially in the long-wavelength infrared (8)(9)(10)(11)(12) lm) and very-long-wavelength infrared (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30) lm) regions. For this SL material, the absorption coefficient near the band-edge is reduced as the cutoff wavelength of the material is made longer.…”

“…This issue can be circumvented in interband cascade infrared photodetectors (ICIPs) where a discrete multiple absorber architecture is used to increase the collection efficiency of photogenerated carriers and reduce the detector noise [6][7][8][9][10][11]. In this type of infrared photodetector, an individual absorber is made of an InAs/GaSb type-II SL and sandwiched between hole and electron barriers to form one cascade stage.…”

Calculations of Dark Current in Interband Cascade Type-II Infrared InAs/GaSb Superlattice Detector

“…In order to explain I−U characteristics of ICPs the theoretical dark current model proposed by Hinkey and Yang is used [9]. The transport region plays a role similar to the depletion region in a conventional p−n junction to direct current in one direction.…”