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.
