Fig. 1. (Color online) Diagram of the structures under study. Indium doping layers are present only in some structures.

Fig. 2. (Color online) (a) Kinetics of the resistance of the structure 170301_p during the transition from the dark to the illuminated state. (b) and (c) Kinetics of the resistance of the structures (b) 091225_n and (c) 100708^*_n during the transition between different illuminated states.

Fig. 3. (Color online) PPC spectra of structures (a) 170301_p, (b) 091225_n, and (c) 100708^*_n. The solid lines correspond to continuous measurements: 1—the sweep is from lower energies to higher ones, 2—from higher to lower ones. The yellow squares and dark hexagons correspond to the steady-state resistance values obtained via point-by-point scanning with the illumination on and after the illumination was turned off, respectively. For structures 091225_n and 100708^*_n, the electron concentration values determined from transport measurements are also indicated by asterisks. The horizontal dashed lines indicate the dark values of resistance and concentration.

Fig. 4. (Color online) Spectra of relative conductivity change of the CdHgTe-based QW heterostructures at T = 4.2 K. The zero level means that the conductivity coincides with the 'dark' one, positive values correspond to a positive PPC, and negative values correspond to a negative PPC. The level –1 means no conductivity. The main spectral features are indicated by inverted numbers. Solid arrows indicate the position of features 2 and 3. Dash–dotted arrows mark the energy of feature 3 plus 0.315 eV. The vertical dotted line indicates the value of the CdTe bandgap (E_g^CdTe), the dash–dotted line indicates the energy difference between the conduction band and the deep level in the CdTe cap layer, and the dashed line indicates the position of feature 4.

Fig. 5. (Color online) Spectra of relative conductivity change of the CdHgTe-based QW heterostructures at T = 77 K. The zero level means that the conductivity coincides with the 'dark' one, positive values correspond to a positive PPC, and negative values correspond to a negative PPC. The level –1 means no conductivity. The main spectral features are indicated by inverted numbers. Solid arrows indicate the position of features 2 and 3. Dash–dotted arrows mark the energy of feature 3 plus 0.315 eV. The vertical dotted line indicates the E_g^CdTe value, and the dash–dotted line indicates the energy difference between the conduction band and the deep level in the CdTe cap layer.

Fig. 6. (Color online) Typical energy diagram of the studied structures at T = 4.2 K using the structure 091225_n as an example. The energies are given in meV. E_c is the position of the bottom of the conduction band, E_v is the position of the top of the valence band, E_so is the position of the top of the spin-split band. The dotted lines with numbers show the transitions that cause the corresponding features in the PPC spectra. The gray lines with letters show the hypothetical transitions considered while interpreting feature 3 (see text).

Fig. 7. (Color online) Theoretical dependences of the energy between the spin-split band in the Cd_1–xHg_xTe barrier and the conduction band of the CdTe cap layer (solid line), as well as the experimental positions of feature 2 (symbols), obtained from the analysis of the PPC spectra measured at T = 4.2 K (a) and T = 77 K (b). Each symbol corresponds to a specific structure. For the left figure, the data from Ref. [33] are additionally shown by triangles.

Fig. 8. (Color online) Dependences of the spectral position of feature 3 (symbols) and the energy of the transition from the deep level located 0.315 eV above the top of the valence band of CdTe to the conduction band of the Cd_xHg_1–xTe barrier (solid line) on the cadmium fraction x in the barrier at T = 4.2 K (a) and T = 77 K (b). Each symbol corresponds to a specific structure. For the left figure, the data from Ref. [33] are additionally shown by triangles. The calculated energies of the hypothetical a–d transitions are also additionally indicated in the left figure (see text).

Fig. 9. (Color online) Dependences of the oscillation period in the PPC spectra obtained at T = 4.2 K (solid symbols) and at T = 77 K (open symbols) of all studied structures on the quantum energy of the incident radiation. Symbols of the same shape correspond to a specific structure. Additionally, data from the Ref. [35] (crosses) are given, in which HgTe/CdHgTe heterostructures with different cap layers were studied. Solid lines show similar dependencies at T = 0 K calculated for different compositions of bulk Cd_1–xHg_xTe (the left boundary of the line corresponds to the bandgap). The inset shows the PPC spectra of some structures in the energy range of 0.7–1.6 eV (the scale along the ordinate axis is chosen individually for each spectrum). The spectra clearly show oscillatory behaviour, the maxima of oscillations are marked by thin vertical lines.

Table 1. Parameters of the structures under study. The parameters specified based on the results of measuring the magnetoabsorption spectra and/or photoconductivity spectra at different temperatures are given in brackets. An asterisk in the number means that the structure was annealed, which should lead to the formation of additional acceptors (mercury vacancies). The subscript in the number indicates the type of low-temperature dark conductivity. Band spectrum types: N—normal, GL—gapless, I—inverted. R_dark—resistance of the sample after cooling in the absence of special illumination. n (p) is the 'dark' concentration and type of charge carriers, μ_n(μ_p) is the corresponding mobility.