Analysis of dispersion-dependent spectral response of mid-infrared in GaAs/GaAsSb photodetectors

Abstract

Semiconductor photodetectors working in the mid-infrared range of operation are important because of their extensive applications in chemical sensing, gas monitoring, medical diagnostics, infrared imaging, molecular absorption spectroscopy, and freespace communications. InP based quantum cascade structures operating at room temperature has been used to design mid-IR optoelectronic devices such as lasers, sensors and detectors. However, wavelength less than 3.8 m is difficult to achieve with quantum cascade structures on account of performance degradation. On the other hand, wavelength more than 2.1 m is difficult to achieve with InGaAs/InP interband devices because of strain relaxation. So, the design of efficient devices that will cover the 2.1–3.8 m wavelength region is of great significance. HgCdTe is used to design sensors and detectors in this region but it suffers from low yield and lack of uniformity. To solve this problem InGaAs/GaAsSb quantum structure on popular and inexpensive substrate, InP can come a long way, because the type-II band alignment of these devices provides small enough energy gap to produce wavelength in the desired region (2.1–3.8 m). The design of InGaAs/GaAsSb type-II photodetector is challenging as a transition occurs from a valance band state in GaAsSb to a conduction band state in InGaAs. The valance and conduction band structures of the superlattice need to be solved using a rigorous technique such as 8 band k p method. Although k p method is quite popular in determining the characteristics of quantum heterostructures, the development of a robust and compact k p simulator for type I, type II, strained, unstrained, single and multiquantum well structures is challenging. In present work, we have developed an extensive 8 band k p simulator that can be used to compute the band structure and dispersion relation of a wide range of materials. As our simulator is temperature and strain inclusive, it shows better accuracy and robustness in the computation of device bandstructure. The wavefunction and energy dispersion relation derived from the simulator has been later utilized to compute the absorption coefficient of our chosen In- GaAs/GaAsSb material system. The absorption coefficient of InGaAs/GaAsSb/InP type II quantum well system is not extensively studied in available literature. Present work contributes in this area to reduce the gap between available experimental and simulation work. Finally, we have designed structure that produces 1.3 times stronger absorption and 1.7 time weaker dark current than the lattice matched structure. We have also operated a device at higher wavelength (3.7 m) at room temperature.