The temperature- and bias-dependent photocurrent spectra of very long wavelength GaAs/AlGaAs quantum well infrared photodetectors (QWIPs) are studied using spectroscopic measurements and corresponding theoretical calculations. It is found that the peak response wavelength will shift as the bias and temperature change. Aided by band structure calculations, we propose a model of the double excited states and explain the experimental observations very well. In addition, the working mechanisms of the quasi-bound state confined in the quantum well, including the processes of tunneling and thermionic emission, are also investigated in detail. We confirm that the first excited state, which belongs to the quasi-bound state, can be converted into a quasi-continuum state induced by bias and temperature. These obtained results provide a full understanding of the bound-to-quasi-bound state and the bound-to-quasi-continuum state transition, and thus allow for a better optimization of QWIPs performance.
The avalanche multiplication of photocurrent in InAs/InGaAs quantum dot infrared photodetectors (QDIPs) has been observed in the temperature range from 20 to 80 K. The avalanche onset voltage Vth, being larger than 1.2 V at T<55 K, is reduced to less than 0.8 V at T>60 K. This singularity of Vth indicates that intermediate-band-assisted avalanche multiplication is achieved in our dots-in-well structure, which benefits from the abrupt change of the electron occupation of the intermediate band at a temperature of approximately 55 K. The remarkable reduction of Vth for QDIP is a useful enhancement in the infrared detector’s performance.
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