Cyclotron resonance of extremely conductive 2D holes in high Ge content strained heterostructures

Cyclotron resonance (CR) and magneto-transport have been studied in pulsed (40 T) and quasi-static (15 T) magnetic fields, for holes in highly conductive “pure Ge” strained channels. Modulation doped structures with 10-20 nm thick “Ge” quantum wells (which in fact contained 2-5% Si) were grown (i) by hybrid-epitaxy, combining UHV-CVD for the Si0.4Ge0.6 strain-tuning buffer and low temperature SS-MBE for the “Ge channel” [1], with a hole mobility of 27,000 cm2/Vs at a density of 1.8 ×1012cm−2 that represents a higher conductance than other “high-Ge” heterostructures and (ii) by LEPE-CVD [2] on a Si0.3Ge0.7 buffer, having a mobility of 47,000 cm2/Vs at 0.61012 cm-2.

Very good CR lines were obtained for all samples tested across the wavelength range 70 μm< λ <871 μm and for temperatures 4-200 K. These CR results confirmed the presence of 2DHGs with extremely high mobility, above 55,000 cm2/Vs at 4K, and the lowest cyclotron effective mass mCR= 0.11 m0 agrees well with that obtained from Shubnikov-de Haas oscillations (SdHO). At the highest excitation energies (70-96μm), a splitting of the CR line appeared. This is consistent with beating seen in pulsed field SdHO that provides evidence for the, unexpected, occupation of two hole subbands.

The results will be compared to calculations of the hole Landau levels and CR transition energies as a function of magnetic field using a 4x4 Luttinger Hamiltonian that also includes strain and the real triangular profile. A full interpretation requires the effects of hole-hole interactions (HHI) on both CR and SdHO. These HHIs are extremely important for such high mobility holes, as we previously demonstrated by considering transport in the diffusive and ballistic regimes [3].

1. R J H Morris et al 2004 Semicond. Sci. Technol. 19 L106-L109.
2. Benjamin Rößner, Giovanni Isella and Hans von Känel 2003 Appl. Phys. Lett. 82, 754-756.
3. I.B. Berkutov et al 2006 Low Temp. Phys. 32 No 7 683-688.