The detection of terahertz waves by semimetallic and by semiconducting materials

We present a survey of photoresponse (PR) measurements of various devices containing quantum wells (QWs) of HgTe of various widths d QW and of InSb. By varying d QW for HgTe, the material properties of the QW material change from semiconducting to semimetallic as d QW is increased above a value of about 6nm. We have studied the PR of devices made from Cd x Hg 1 − x Te / HgTe / Cd x Hg 1 − x Te wafers with values of the QW width in the range of 6 nm ≤ d QW ≤ 21 nm . Only for samples with semimetallic HgTe QWs, a measurable PR could be detected. However, our investigations of samples made from Al x In 1 − x Sb / InSb / Al x In 1 − x Sb wafers gave evidence that a measurable PR also can appear from devices with a semiconducting QW. Both cyclotron-resonant (CR) and nonresonant (bolometric, BO) interaction mechanisms can contribute to the PR signal. Whereas the CR contribution is dominant in Al x In 1 − x Sb / InSb / Al x In 1 − x Sb samples, in Cd x Hg 1 − x Te / HgTe / Cd x Hg 1 − x Te samples the behavior is more complex. In a sample with d QW = 8 nm , the PR is clearly dominated by the BO contribution. In the PR of another sample of d QW = 12 nm , both contributions (BO and CR) are present. The sample of d QW = 21 nm shows a PR with not clearly separable BO and CR contributions.