PhD Dissertation Prospectus Defense: Jonathan Schuster

Advanced numerical modeling of infrared pixel arrays incorporating photon-trapping structures -- Date: Wednesday, January 30, 2013, 1:30pm -- 8 Saint Marys Street, Room 339 -- Chair-Advisor: Enrico Bellotti (ECE) Committee: Roberto Paiella (ECE), Michelle Sander (ECE), Marion Reine (Photon Detector Physics) -- Infrared detectors are well established as a vital sensor technology for both military and defense applications as well as in an emerging commercial market. Due to the expense and effort required to grow pixel arrays, it is imperative to develop numerical simulation models to perform predictive device simulations which assess device characteristics and design considerations. Towards this end we have developed a robust three-dimensional (3D) numerical simulation model for IR detector pixel arrays. We have used the finite-difference time-domain (FDTD) technique to compute the optical characteristics including the reflectance and the carrier generation rate in the device. Subsequently, we employ the finite element method to solve the drift-diffusion equations to compute the electrical characteristics including the I(V) characteristics, quantum efficiency and the crosstalk. We first use our 3D numerical model to study a new class of detector based on the nBn-architecture. This detector is a unipolar unity-gain barrier device consisting of a narrow-gap absorber layer, a wide-gap barrier layer (BL), and a narrow-gap collector layer. We use our model to study the underlying physics of these devices and to explain the anomalously long lateral collection lengths for photocarriers measured experimentally. Our 3D simulations reveal that the BL has a "built-in" potential well for holes that forms a channel in which holes are "trapped," allowing them to diffuse very long distances. Furthermore, we assess this effect by calculating the quantum efficiency and crosstalk in a 3x3 pixel array. Secondly we investigate the crosstalk in HgCdTe photovoltaic pixel arrays employing a photon-trapping (PT) structure realized with a periodic array of pillars intended to provide broadband operation. We have found that, compared to non-PT pixel arrays with similar geometry, the array employing the PT structure has a slightly higher optical crosstalk. However, when the total crosstalk (optical + losses due to photogenerated carriers diffusing into neighboring pixels) is evaluated, the PT region drastically reduces the total crosstalk; making the use of the PT structure not only useful to obtain broadband operation, but also desirable for reducing crosstalk in small pitch detector arrays.