Simulation of Quantum Infrared Photodetectors

Abstract

The topic of research is concerned with modelling and simulation of high temperature long wavelength infrared quantum photodetectors using advanced finite element methods. The aim is to devise novel designs based on quantum well structures to improve quantum efficiency, and operating temperature. These new designs rely on quantum confinement of electrons and holes inside a mixture of materials within which the energies of the carriers become discrete and differ from those observed in bulk materials. Type II InAs / GaSb superlattices is one of these meta–materials which offer a large flexibility in the design of infrared photodetectors, including the possibility to adjust the detected wavelength over a very wide range and to realize a suitable absobers’ unipolar barriers to suppress dark current while maintaining a significant portion of photocurrent at high temperatures. In order to validate this interest, A set of rigorous modelling tools based on multi-band k· p band structure theory and Boltzmann transport theory has been developed, which provide a better understanding of the electronic structure and transport in these heterostructures. The framework takes into account in particular the effect of the intrinsic strained property of the unintentional interfaces on the electronic structure and the optical properties. First, the finite element method is used to solve 8 × 8 k · pHamiltonians for InAs/GaSb superlattices with type II alignment to compute the optical and materials’ characteristics. For InAs and AlAsSb and alloys based detectors, An optical material library has been developed to generate all the needed bulk material properties. Secondly, the transfer matrix method or the Beer-Lambert law is used to compute the optical generation profiles in the device. Finally, the the finite volume method has been employed to solve the transport equations to compute the dark- and photo- currents, quantum efficiency among other device properties. Using this tools, new structures based on nBn and nBp architectures have been designed, with optimized design, which contribute to the realization of mid- and long- wave infrared photodetector based on Type-II superlattices InAs / GaSb material system as well as InAs/AlAsSb alloy mterial system. The developed model allows to study the underlying physics of these devices and to explain the factors limiting the device performances. Based on the simulation results, detectors involving absorbers with period composed of 14 Mono-Layer (ML) of InAs and 7 ML of GaSb was found to have a band gap wavelength close v to 11 μm and exhibit a lower dark current than those with period mainly composed of GaSb. The designed LWIR barrier device consists of a 4 μm thick p-type InAs-rich 14 ML InAs / 7ML GaSb LWIR T2SL absorber, a 200 nm thick p-type InAs/AlSb SL barrier and an n-type InAs-rich 14 ML InAs / 7ML GaSb LWIR T2SL contact layer. The 16.5ML InAs / 4ML AlSb superlattice of the BL is designed to give a smooth conduction band alignment and a large VBO of nearly 400 meV with the AL. The optimum doping level of absorber, barrier and contact layer are found to be 1 × 1016cm3, 5 × 1015cm3 and 1 × 1016cm3 respectively. This nBp detector design exhibits at 77 K a diffusion limited dark-current down to -300 mV with a dark-current level plateau as low as 8.5 × 10−5A/cm2 which is more than one order of magnitude lower compared to a similar PIN photodiode. Furthermore, this value is near the level of the MCT ‘rule 07’ demonstrating that InAs/GaSb SL detectors may provide new opportunities to replace the MCT technology in the LWIR spectral window given the MCT material instability problem at longer wavelengths. Moreover, we have demonstrated that the presence of the majority carriers’ barrier improves the current performances and the operating temperature over the standard PIN device. A temperature improvement of 20 K was found for a given current density of 2x10−4 A/cm−2 compared to a similar LWIR PIN device working at 60 K.