Cyclotron resonance in ultra-low-hole-density narrow p-type GaAs/(Al,Ga)As quantum wells

Abstract

The cyclotron-resonance behavior of a series of p-type, low p s , asymmetrically doped ͑311͒A quantum wells has been measured over two orders of magnitude in energy. Landau levels for the structures studied have been calculated for comparison with experiment. The calculations use a rotated Luttinger Hamiltonian and invoke the axial approximation. In the quantum limit and at certain far-infrared energies we observe two resonances widely separated in field. We find at the lowest fields that the samples exhibit a light effective mass. For the narrowest quantum well the cyclotron resonance ͑CR͒ broadens and shifts to a slightly lighter mass into the quantum limit, above about 2 T. The CR energy is modeled by inter-Landau-level transitions from the highest level, and a discontinuous evolution to a higher effective mass, observed as the second resonance above 8 T, is explained by crossing of the highest two Landau levels, as modeled in the calculation. The discontinuous evolution to a higher mass is found to shift to lower fields as the well width increases, as suggested from the modeling. For the wider quantum wells the influence of additional anticrossings at intermediate fields, due to the proximity of the second subband, is observed. CR energy for these samples is adequately modeled at energies above and below the region of subband anticrossing. The limitations of the modeling procedure have been discussed and a number of features of the experimental data are explained qualitatively in terms of the expected modifications to the hole Landau-level structure when full Landau-level mixing is incorporated into the modeling. The influence of hole-hole interactions and factors influencing the CR scattering time are also discussed briefly. ͓S0163-1829͑97͒08804-8͔

Exciton Exchange between Nearly-Free and Acceptor-Bound States of a Positive Trion Assisted by Cyclotron Excitation

“…The pres-ence of a pair of CR-AX + replicas is a consequence of the fact that the allowed (by the conservation of angular momentum and spin) recombination of the AX + ground state (labeled by the 3h spin of 1/2 and the total 3h+e angular momentum projection of −1) occurs to a pair of spin-singlet and triplet states of the A + , separated by an exchange gap. Comparison of the slopes of CR-AX + and AX + yields a difference of 0.35 meV/T, which agrees very well with the hole cyclotron energy determined earlier from the cyclotron resonance of the low-density GaAs/ AlGaAs quantum wells [6] (interpolation of those results for the 22 nm width gives 0.28 meV/T). The effective mass corresponding to the measured slope is m h = 0.33.…”

Millimeter wave transmission spectroscopy of gated two-dimensional hole systems

“…A Gaussian curve can be approximately fit to the differential transmission peaks, whose peak location, B min , and full width half max, C, yielded the effective mass and cyclotron scattering time of m à ¼ eB min =2pf in terms of m e , and s S ¼ m à =eC, respectively. In our frequency-dependence data from the 20 nm QW 2DHG sample (Figure 3), we note that the transmission minima is directly proportional to the irradiation frequency as we would expect from the cyclotron resonance, which also coincides with the higher frequency results from Cole et al 18 This data allowed us to calculate the effective mass of the hole system to be 0:41m e , confirming the results from Kumar et al 15 and Yuan, although they used different techniques. The values of the scattering time s s at some frequencies show large error bars because of weak signals.…”

Effective mass and spin susceptibility of dilute two-dimensional holes in GaAs

“…46,47 The origin is not fully clear but is likely related to the non-linear dependence of the 2D hole Landau levels on B ⊥ . 33,36 To asses the density dependence of m * , we show a plot of m * , measured at comparable values of B ⊥ ∼ 0.3 T. The plot suggests a slight increase on m * with increasing density.…”

“…We determine m * through analysis of the temperature dependence of the Shubnikov-de Haas (SdH) oscillations. While m * in GaAs 2D holes has been measured via cyclotron resonance experiments, [30][31][32][33][34][35][36] there are no reports of m * measurements in dilute 2DHSs through transport experiments. The latter are useful because m * deduced from transport measurements should reflect interaction effects while, due to the Kohn theorem, 37 m * measured in cyclotron resonance experiments does not.…”