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Using a free-electron laser(FEL) source, we have studied the two-photon-absorption (TPA) effect in GaAs/AlGaAs quantum-well infrared photodetector (QWIP). The TPA-induced photoresponse in QWIPs has been measured under different FEL excitation power by the photoconductivity method. The effective-mass approximation theory is used for the QWIP structure to explain the photoresponse behavior. It is demonstrated that the TPA-induced photocarrier density is proportional to the square of the excitation power. Based on the experimental results, the TPA coefficients of QWIPs were obtained to be 0.0045, 0.0030, 0.0103, and 0.0061 cm/MW for the excitation lines of 10.6, 10.7, 11.9 and 13.2 μm, respectively. The dependence the TPA coefficients on the excitation wavelength is explained by our theoretical model. [ABSTRACT FROM AUTHOR]

Abstract: Signatures associated with electronic states confined in two strained In x Ga1–x As/GaAs single quantum wells have been observed in its piezomodulated (PzR) and photomodulated (PR) reflectivity spectra. One comparison of the relative intensity between 11H and 11L signatures in PzR of GaAs/In0.14Ga0.86As SQW emphasizes the contribution of strain dependence of energies of the confined states; the other comparison of corresponding confined states between PzR and PR spectra in both samples has been introduced to interpret the discrepancy of the relative intensity in term of modulated strength, and the calculated ratio of energy shifts induced by strain to that of produced by surface electric field agree with the experimental observation. [Copyright &y& Elsevier]

Abstract: Near-field effect has been recognized to play an important role in optical coupling of multiple quantum well infrared photodetectors (QWIP). Both the optical near-field effect and the plasmonic effect in the quantum well active region of QWIP device have been studied by the finite difference time-domain (FDTD) method at the optical frequency of 4.2THz. Our numerical results indicate that both the near-field effect and the plasmonic effect can induce an evanescent wave with the electrical component being parallel to the growth direction of quantum well. The induced electrical component in the QWIP growth direction is 2.5 times larger than that of the incident optical fields. The induced polarization can increase the optical coupling efficiency of QWIP and the detectivity of QWIP can be improved at 4.2THz. [Copyright &y& Elsevier]