Fig. 1. (Color online) (a) Quantum well structure diagram. (b) Hall bar structure diagram and test schematic diagram.

Fig. 2. (Color online) The corresponding range of strains of LS (lightly-strained QW), SS (standard-strained QW), HS (heavily-strained QW) and ΔE(HH−LH) is calculated using VSAP.

Fig. 3. (Color online) (a) HRXRD analysis of the lightly-strained QW. The green line shows the quantum well shifting leftward as strain increases. (b) AFM analysis of the lightly-strained QW (10 μm × 10 μm R_q = 2.03 nm).

Fig. 4. (Color online) SdH oscillation of each sample at near saturation density at 250 mK. (a) Transverse resistance. (b) Longitudinal resistance and fill factor ν.

Fig. 5. (Color online) Electrical and magneto-transport measurements at 250 mK of Hall-bar shaped HFET. (a) Mobility μ vs carrier density p_2DHG. Transport parameters are shown in Table 1. In the local zoom-in of (a), the blue curve corresponds to the fitted curve of mobility μ versus carrier density p at low carrier density, while the red curve corresponds to the fitted curve at high carrier density. (b) Longitudinal conductivity σ_xx vs carrier density p_2DHG. The green curve is fitted by σ_xx ∝ (p_2DHG − p_p)^p, p = 2. The confidence intervals of both fits are larger than 0.999.

Fig. 6. (Color online) (a) Quantum well structure model. (b) Quantum well barrier energy band model under gate voltage control.

Fig. 7. (Color online) (a) Correlation curve between barrier layer components and percolation density. (b) Correlation curve between quantum well thickness and percolation density. (c) Correlation curve between quantum well depth and percolation density. (d) A contour map of p_p constructed by overlaying our calculated data on the thickness-depth phase diagram.

Fig. 8. (Color online) The density of tunneling carriers at 250 mK corresponds to (a) a quantum well (QW) depth of 20 nm, where tunneling does not occur; (b) a QW depth of 30 nm, with a very small probability of tunneling; (c) a QW depth of 40 nm, with a significantly higher probability of tunneling.

Fig. 9. (Color online) The amplitude change is fitted as a function of T, normalized at Δρ₀ = Δρ (T₀ = 250 mK). The red solid circle corresponds to the HS sample with an effective mass of 0.091 m₀; the black solid diamond corresponds to the SS sample with an effective mass of 0.083 m₀; and the blue solid circle corresponds to the LS sample with an effective mass of 0.073 m₀.

Fig. 10. (Color online) Mixed transport model of light and heavy hole subbands. (a) Light and heavy hole subbands under strain. (b) Carrier transport mode in which only the heavy hole subband participates under strain. (c) Mixed transport mode of light and heavy hole subbands under strain. (d) State density DOS (density of states) distribution diagram of the Fermi level E_F corresponding to the light and heavy hole subbands.