At present, molecular beam epitaxy is used to fab ricate high perfection heterostructures with HgTe quantum wells (QWs) of varied thicknesses, which possess interesting physical properties. In particular, it has been shown that, in the case of fairly wide wells (20-30 nm), the HgTe layer is semimetallic, i.e., its conduction and valence bands overlap [1]. Structures of this kind have been studied by magnetotransport methods [2] and by cyclotron resonance techniques in the microwave spectral range [3]. It has also been reported that photoconductivity is observed in struc tures of this kind [4][5][6][7]. Two different mechanisms that account for the origin of the photoconductivity signal have been suggested, namely, the bolometric [5] and cyclotron resonance mechanisms [4]. Recently, detailed studies [7] of photoconductivity in structures with HgTe/CdHgTe QWs of varied lengths have con firmed that the main photoconductivity mechanism is bolometric. However, in wide (20 nm and more) semi metallic wells, the issue of the photoconductivity mechanism remains open. Solution of this issue is very important, in particular, for determining the carrier effective mass from photoconductivity spec tra. Obviously, the thus obtained effective mass will be incorrect in a case where the bolometric mecha nism is predominant.In this study, we present evidence that the photo conductivity signal obtained for wide HgTe/CdHgTe wells simultaneously contains both cyclotron reso nance and bolometric components, with the predom inance of the latter. The large value of the photoelec tric signal, observed in our experiments, indicates that structures of this kind are promising for the develop ment of photodetectors for the terahertz spectral range.As objects of study, we used HgTe/CdHgTe struc tures grown by molecular beam epitaxy with the (013) surface orientation. The well thickness was 20.5-21 nm. For more details on methods used to fabricate structures of this kind, see [8].We studied 2 × 4 mm rectangular samples. Strip ohmic contacts were fabricated along the narrow edge of a sample by the firing in of indium. The results of the study are presented for a sample with an electron concentration of 1.46 × 10 11 cm -2 , found from magne toresistance oscillations.As a source of terahertz radiation, we used a pulsed laser, which operated in the cyclotron resonance mode (CR) in p Ge, with a pulse duration of <1 μs and a tunable magnetic field B in the wavelength range 100-160 μm (1.87-3 THz) [9]. We measured variations in the voltage drop across the contacts under the action of terahertz radiation pulses in magnetic fields near the filling factors ν = 2-4.The dependences of the photoconductivity signal on the magnetic field are shown in Fig. 1 for three dif ferent laser emission frequencies. The same figure demonstrates the dependence of the sample's resis tance on a magnetic field, measured in the double contact configuration. The figure clearly shows two plateaus in the dependence of the resistance close to the magnetic field inductions B = 3 ...
