| Popis: |
A terahertz photodetector receives terahertz frequency in the range of ~0.3 to ~30 THz from a source in the input terminal and transforms the input signal, typically into an electrical signal. In general, a terahertz detector can be able to differentiate photons of different energies. A broad energy response is desirable from a detector, though a narrowband with minimal FWHM is desirable in some applications. In this chapter, the author is interested of the kind of detectors where the terahertz radiation interacts with the bound carriers in a heterostructure and presented desired transition. The quantum dot intersublevel photodetector (QDIP) is such kind of detector which creates a great interest among the researchers. Room-temperature terahertz detection has been reported with QDIPs by various groups. THz QDIP works on the principle of carrier transitions from lower subband to excited sate while interacting with a photon of required energies. The photons may be absorbed by exciting carriers in the valance or conduction band of a dot and excited to higher state from the ground state. Quantum dot size and shape doping concentration affected the absorption coefficient and in turn overall output of the detectors. Inherent properties of QDIPs such as normal incidence interaction of light and enhanced lifetime of photo-excited electrons are few crucial advantages for such structures. There are several valuable reports on QD working as a detector with minimal dark current attributed to the 3D quantum confinement and diminished thermionic emissions. Detectivity and responsivity are the two quantities which define the reliability and quality of a detector. Ideally, a terahertz detector should have large value for responsivity following the interaction of individual terahertz photons with the confined carriers. The dependency of the absorption coefficient and transition energies on the QD size and size distribution of the QD system has already been explained by the author in his earlier work. In this chapter, the author discussed the basic working principle of the QDIP while explaining the overall sensitivity of QDIP changes depending on the QD morphology and choice of materials. The chapter concludes by taking notes of the drawbacks of QDIPs in terahertz detection and a scientific approach to overcome those issues. |
