Probing the semiconductor to semimetal transition in InAs/GaSb double quantum wells by magneto-infrared spectroscopy

We perform a magnetoinfrared spectroscopy study of the semiconductor to semimetal transition of InAs/GaSb double quantum wells from the normal to the inverted state. We show that owing to the low carrier density of our samples, the magnetoabsorption spectra evolve from a single cyclotron resonance peak in the normal state to multiple absorption peaks in the inverted state with distinct magnetic field dependence. Using an eight-band Pidgeon-Brown model, we explain all the major absorption peaks observed in our experiment. We demonstrate that the semiconductor to semimetal transition can be realized by manipulating the quantum confinement, the strain, and the magnetic field. Our work paves the way for band engineering of optimal InAs/GaSb structures for realizing novel topological states as well as for device applications in the terahertz regime.

Figure 1

(a) Schematic band diagram of AlSb/InAs/GaSb/AlSb QW structure. The energy zero is referenced to the conduction-band edge of bulk InAs. The top and bottom of each color coded blocks indicate the energies of the conduction- and valence-band edges for each material. $E_0$ and $H_0$ illustrate the lowest electron subband in InAs and the highest hole subband in GaSb, respectively, due to quantum confinement. (b) Evolution of the band alignment in InAs/GaSb DQWs, as the width $d$ of the InAs QW increases (from left to right) while fixing the GaSb QW width. Blue and red curves represent the lowest electron and highest hole subbands, respectively. (c) Epistructure of MBE grown InAs/GaSb DQW samples.

Figure 2

(a) Normalized magnetoabsorption spectra, $-T\left(B\right)/T(B=0)$, for the slightly inverted InAs/GaSb DQW sample ($d=10$ nm) at selected magnetic fields. (b) Normalized magnetoabsorption spectra for the heavily inverted sample ($d=15$ nm) in the high-field (top panel), intermediate-field (middle panel), and low-field (bottom panel) regions. For best presentation, the spectra are normalized to 11, 7, and 0 T, respectively, for each panel. The star symbols point to $B$-independent spectral features originating from the normalization process. The dashed lines indicate the major absorption peaks observed in the experiment. (c,d) Calculated magnetoabsorption spectra using the eight-band PB model, in comparison with the experimental results in (a) and (b). In all panels, the spectra are offset vertically for clarity.

Figure 3

Calculated energy levels as a function of magnetic field for (a) $d=8$-, (b) 10-, (c) 13-, and (d) 15-nm InAs/GaSb DQW samples. The PB manifold is color coded based on the index $p$, and the dashed line shows the evolution of $E_F$ as a function of magnetic field. The dashed arrows indicate the major transitions, $T_0,T_1$, and $T_2$, commonly observed in our samples. The dotted lines mark the onset ($B_c$) of the magnetic field driven transition from the inverted to the normal state.

Figure 4

Magnetic field dependence of major absorption peaks, both experimental and theoretical, for the $d=8$- (inset to panel a), 10- (a), 11- (b), 13- (c), and 15-nm (d) DQW samples. The blue (red) solid lines represent the manifold-resolved interband (intraband) transitions. For simplicity, we only label the commonly observed transitions, $T_0,T_1$, and $T_2$, in our samples. Complete assignment of all transitions can be found in Table S2. The red dashed lines indicate the diminishing absorption peaks (Pauli) blocked when the corresponding level crosses above the Fermi energy.

Figure 5

Diagram describing the magnetic field driven semimetal to semiconductor transition from the inverted to the normal state, with and without strain. The width of GaSb QW is fixed to 5 nm. For demonstration purpose only, we omit the lengthy self-consistency calculation in this diagram.