DX -like centers in InAsGaAs QDIPs observed by polarization-dependent Fourier transform infrared spectroscopy

In order to decrease dark current density and improve spectral response tunability of quantum dot infrared photodetectors (QDIPs), it is critical to understand how dopants are incorporated into quantum dot active regions. In this article, polarization-dependent Fourier transform infrared absorbance spectroscopy is used to measure intraband absorption in InAsGaAs QDIP heterostructures featuring different molecular beam epitaxy remote doping schemes. In addition to a QD absorbance peak near 90 meV, a peak at 405 meV is observed. This peak at 405 meV demonstrates signature characteristics of DX centers in III-V semiconductors, such as spherical symmetry, thermal activation of trapped carriers with increasing temperature, and dependence of absorbance peak magnitude (and thereby DX center concentration) on doping concentration and doping scheme. A conduction band energy diagram for the observed DX -like center and the corresponding optical ionization process is proposed. In addition, the effect of these DX -like centers on measured dark current density at T=50 K of the corresponding fabricated QDIPs is discussed.