Quantum dot infrared photodetectors in new material systems

Infrared detectors were implemented on InAs self-assembled quantum dots fabricated using Stranski–Krastanov growth mode on InAlAs matrix, lattice matched to InP (0 0 1) substrates. These dots grow with a shape of small elongated boxes, with their long axis along the [ 1 1 0] direction, and with a high concentration of 7×10 10 cm −2 . Photoconductive measurements were performed in all three polarizations. Rich spectra in the range of 50–500 meV, with different polarization selection rules were observed. The bias dependence of peak intensity of the intraband transitions serves as an additional tool to identify their origin. Some of the peaks, which increase linearly with bias, are attributed to bound-to-continuum transitions. Others, which appear only at larger biases, and increase superlinearly, are due to bound-to-bound transitions. The magnitude of detector responsivity at normal-incidence is similar to that obtained for polarization normal to the layers, and is comparable to that achieved in QWIPs. BLIP conditions prevail at 77 K for integral photocurrent response at F#1. The effect of unintentional doping is discussed. It is shown that this doping can be destructive for detector operation unless the density of dots is large.