Modulation–Doped Multiple CdTe Quantum Wells as THz Detectors, Filters and Emitters

We studied quantum structures grown by a molecular beam epitaxy comprising CdTe quantum wells (QWs) modulation-doped with iodine donors in Cd
1-x
Mg
x
Te barrier (x=0.2 or 0.3). Experiments were carried out at liquid helium temperatures at magnetic fields up to 9 T. Samples studied differed by the number of and the distance between QWs, the thickness of spacer and the doping level. Magnetotransport measurements revealed electron concentrations of the order 10
¹¹
cm
^-2
per well and a one-carrier conductivity with only a slight admixture of a parallel transport in some samples. Transmission of THz radiation in the range 0.1 – 1.0 THz showed a well-defined cyclotron resonance minimum in the case of single QWs which developed into Shubnikov – de Haas – like oscillations in samples with multiple QWs. Such oscillations were also observed in THz photocurrent and were interpreted as resulting from free-carrier absorption. The study carried out on a large number of samples with different technological parameters made it possible to select optimal structures based on CdTe/Cd
1-x
Mg
x
Te modulation-doped quantum wells as THz detectors (resonant or non-resonant) for applications in magnetic fields at low temperatures. Multiple quantum wells were also shown to be magnetic-field-controlled emitters of THz radiation.