Role of quantum capacitance in coupled low-dimensional electron systems

Abstract

We have investigated the charging behavior of a layer of self-assembled InAs quantum dots placed in close vicinity to a two-dimensional electron gas ͑2DEG͒. As the gate bias is changed, the number of electrons in each system is altered simultaneously. Based on the quantum capacitance of the involved layers we develop a general model to determine the charging state of coupled low-dimensional systems from capacitance-voltage ͑CV͒ spectroscopy. The model is then applied to the special case of a layer of self-assembled quantum dots coupled to a 2DEG. As a complementary method, we have employed Hall voltage measurements. We find that the measurement of the two-dimensional carrier density through lateral transport provides a direct insight into the vertical charging process of the quantum dot system. Six individual charging peaks related to the occupation of the s and p shells of the dots can be resolved. In agreement with results from CV spectroscopy, Coulomb blockade and quantization energies can be extracted. Moreover, the Hall measurement offers a higher peak-to-valley ratio and a better estimate for the number of simultaneously charged dots than the capacitance data.

Room-Temperature Hysteresis in a Hole-Based Quantum Dot Memory Structure

“…the GaAs QW have a total localization energy of about 700 meV, which can be estimated from a previous work [13] and from the valence band offset between GaAs and Al 0.9 Ga 0.1 As (500 meV) [14]. According to the simple Drude model, the conductance of a 2DHG depends on the mobility of the carriers and the charge density in the gas [19,20]. If holes are present in the dots, both values change as the scattering probability is increased and the holes transferred to the dots are now missing in the 2DHG.…”

Numerical toolkit for electronic quantum transport at finite frequency

“…ϑ, for each sample, we are able to calculate the velocity of the edge state v g owing to Eq. (51). For the parameters chosen in our calculation, B 20T and the lattice constant a 0 1nm, we have obtained the velocity v g 0.7a 0 t −1 (which corresponds to v g 10 6 m/s), where t = 2 /(2ma 2 0 ) is a hopping parameter of the tight-binding model 29 used to simulate the setup, m -effective mass.…”

“…Among the pioneer works, the extension of the scattering approach to finite frequency initiated in [42][43][44][45][46][47][48] has led to many interesting predictions including the quantum capacitance, finite frequency shot noise, quantum pumping, spin pumping, etc. On the experimental level, apart from the huge corpus of work with quantum-bits (semi-conductor or superconducting based), one observes an increasing interest in high frequency physics, including several striking experiments on quantum capacitance [49][50][51] , quantum inductance 52,53 , or electronic quantum optics [54][55][56][57][58][59][60][61][62][63][64] . On the numerical side, finite frequency physics has attracted comparatively limited interest so far.…”

3 ns single-shot read-out in a quantum dot-based memory structure

“…14,15 First, the electrons confined in the QDs act as a scattering Coulomb potential for the electrons in the 2DEG channel and result in a decreased mobility. Second, the QDs resemble a quantum capacitance, originally introduced by Luryi for quantum wells, 16 by which the electrons in the QDs deplete the 2DEG of carriers through capacitive coupling (field effect).…”